Camera Lens by Philip Greenspun Once you've settled on the subject and the light, you have to decide on the relative prominence of objects in the scene. By moving the camera position back and forth, you can adjust the relative size of objects in the scene. After you're happy with the po sition, you pick a camera lens whose angle of view encompasses all the objects that you want to include in the photo. Objects? Relative prominence? I only want to take a picture of my friend Cyrano! There is only one object in the scene and it is Cyrano's head. Au contraire! The objects in this scene are Cyrano's nose, Cyrano's ears, and Cyrano's eyes. Suppo se that you position your camera 10" from Cyrano's eyes. If his nose sticks out 5" in front of his eyes, then it will be only half the distance from the camera as the eyes and therefore relatively more prominent. Stretch out yourarm right now and compare the size of your index finger to the lines of text on the monitor. Only ab out as big as a paragraph, right? Now close your left eye and bring that same finger in until it is just in front ofyour nose. Note that your finger appears taller than the entire monitor. Aesthetic tip from MIT: when your nose sticks out 5" in front of your eyes, you don't want it to appearrelatively more prominent.Suppose that you actually want this photo as the "before" illustration in a plastic surgeon's advertisement. Well, then haul out the 24mm wide angle lens and you can have a complete portrait taken from 10" away. Suppose that you wish to flatter Cyrano. You'll want to back up until you are separated by the length of a football field. Now his nose is still 5" closer to the camera but that is 5" ou t of 100 yards (note for European readers: 100 yards is just short of half a standard furlong.) So instead of being 50% of the distance to the camera as Cyrano's eyes, the nose is 99.86% of the distance away. It will not be significantly more prominent.
Once you've settled on the subject and the light, you have to decide on the relative prominence of objthe scene. By moving the camera position back and forth, you can adjust the relative size of objects iscene. After you're happy with the position, you pick a camera lens whose angle of view encompasthe objects that you want to include in the photo.
Objects? Relative prominence? I only want to take a picture of my friend Cyrano! There is only one in the scene and it is Cyrano's head.
Au contraire! The objects in this scene are Cyrano's nose, Cyrano's ears, and Cyrano's eyes. Supposeyou position your camera 10" from Cyrano's eyes. If his nose sticks out 5" in front of his eyes, then itonly half the distance from the camera as the eyes and therefore relatively more prominent. Stretch ouarm right now and compare the size of your index finger to the lines of text on the monitor. Only abobig as a paragraph, right? Now close your left eye and bring that same finger in until it is just in frontyour nose. Note that your finger appears taller than the entire monitor.
Aesthetic tip from MIT: when your nose sticks out 5" in front of your eyes, you don't want it to appea
relatively more prominent.
Suppose that you actually want this photo as the "before" illustration in a plastic surgeon's advertisemWell, then haul out the 24mm wide angle lens and you can have a complete portrait taken from 10"
Suppose that you wish to flatter Cyrano. You'll want to back up until you are separated by the length football field. Now his nose is still 5" closer to the camera but that is 5" out of 100 yards (note for Eureaders: 100 yards is just short of half a standard furlong.) So instead of being 50% of the distance tocamera as Cyrano's eyes, the nose is 99.86% of the distance away. It will not be significantly moreprominent.
What about the 24mm lens from this camera position? It will give you a nice photo of the entire stadithe city behind it. Cyrano's face will appear as a portion of a grain of silver on the film. You're now 1yards away from Cyrano so you will need the Mother of All Telephoto Camera Lenses . In fact, accto the formulas in my Kodak Professional Photoguide, if Cyrano's face is 12" high, you will need a 7lens to fill the frame with it. Cyrano will be flattered but considering that a Canon 600mm lens costs
$10,000, the effect on your wallet will not be a happy one.
Exactly how long a camera lens do you need?
How far away is your subject? (in feet)
How high is the object you want to fill the frame?
Submit
Apologies to people from countries that have adopted sensible units.
If sensors and camera lenses were perfect... you would need onl
one lens!
In a perfect world, you would leave the house with only a Canon 14 super-wide lens. You would worabout camera position, secure in the knowledge that the 14mm lens was wide enough to capture the esubject under 99% of conditions. Then if you wanted a picture of just a friend in the middle of the frayou'd crop down to just the center and use that. The result would be the same as if you'd used a 100mportrait lens.
The reason this doesn't work is that lenses and sensors aren't perfect. If you throw away 98% of the athe digital sensor (and/or make a huge enlargement), you can expect to have some pretty crummy loopixels. So if you're sure at exposure time that you will want more magnification, it is best to carry somhigher magnification camera lenses.
The rest of this article discusses what kinds of camera lenses we might want to lug around.
Wide angle camera lenses
With a full-frame digital SLR or 35mm film, a wide angle lens is generally considered anything withlength of 35mm or less.
Here are a couple of snapshots taken with an ancient Canon 20-35/2.8L zoom lens (replaced by Cano16-35mm f/2.8L USM, $1520 (review)). Note that the image on the left, at 20, appears to be significadistorted if you view it from far away. But try clicking on it so that you get a monitor-filling JPEG. Tmove your face in close to the monitor so that you are viewing it from a few inches away. The distortdisappears, right? A wide angle lens does not distort perspective but, if the viewer of the ultimate ima
does not adjust his viewing position, it appears to do so.
(camera closer to car)(camera farther from car)
As a practical matter, most people these days aren't impressed by a wide-angle effect until you get do24mm. Wide angle camera lenses start to get expensive at 20mm ($500) and wider. So good compromthese days are are probably a fixed 24 ($250) or a high-quality 16-35 zoom ($1500). See the Canon aNikon system pages for an idea of what's available.
Normal Lenses
A "normal" or "standard" camera lens is one that produces prints with no apparent wide angle or telepdistortion. In other words, when viewed at a standard distance, a print taken with a normal lens will ato have no unusual perspective. For a camera taking 35mm film, a 50mm lens is considered normal.
Normal lenses are easy and cheap to fabricate. A 50/1.8 costs under $100 and will optically outperfor
most of the lenses in any manufacturer's line. Furthermore, normal camera lenses allow photographyrather low light with no flash or tripod. A yuppie with a mid-range zoom lens has a maximum apertuf/4. A photographer with a 50/1.8 not only saves $200 but is gathering 4 times as much light (2 f-stopWith a standard single-lens reflex (SLR; viewing through the lens), this makes viewing and compositeasier because the viewfinder is 4 times brighter.
If you don't feel like saving $200, you can get a 50/1.4 which will gather another factor of 2 in lighyou are a real wastrel, you can splurge $2500 on a lens like the discontinued Canon 50/1.0. This g16 times as much light as a typical mid-range zoom.
Another common option is the 50mm macro lens. I refer you to my article on macro photography
review of the Nikon 60/2.8 AF lens.
Telephoto Camera Lenses
Telephoto lenses are high-magnification devices. These are for when you are photographsomething from far away either because you want to flatten perspective or because you aunable to approach your subject.
It is difficult and expensive to produce a high-quality telephoto lens. In fact, only in the couple of decades have manufacturers been able to design really high quality 300mm anlonger camera lenses.
Telephoto lenses can be useful for portraits, most often in the 85-180mm range. Photography of largeanimals is facilitated by 300-600mm lenses. Photography of birds starts with a 600mm lens and goesfrom there.
Telephoto camera lenses that serious Canon EOS photographers buy include the following:
• Canon EF 100mm f/2.8 Macro USM , $529 (review), capable of focusing down to 1:1, useful both macro and portraits• 85-135mm super-fast portrait lenses, e.g.,o Canon EF 85mm f/1.8 USM , $380 (review)
o Canon EF 85mm f/1.2L II USM , $1970 (review)
o Canon EF 100mm f/2 USM , $435 (review)o Canon EF 135mm f/2L USM , $999
• 180-200mm macro or portrait-only lens, e.g.,o Canon EF 180mm f3.5L Macro USM , $1370 (review)
o Canon EF 200mm f/2.8L II USM , $769
• Canon EF 300mm f/4L IS USM , $1269 (review) + 1.4X teleconverter lightweight wildlife kit($1,500)• Canon EF 300mm f/2.8L IS USM , $4340 (review) + 1.4X teleconverter heavyweight wildlife($5,000)• Canon EF 600mm f/4L IS USM , $8050 (review) + 1.4X teleconverter bird photography kit($10,000)
For the equivalents in the Nikon system, please see our Nikon System Explained page.
Teleconverters
A teleconverter is a small lightweight intermediate optic that will increase the magnification of a lensreducing its effective aperture. So a 2X teleconverter turns a 300/2.8 into a 600/5.6. A lot of times nephotographers ask me if they can save money by buying a teleconverter and sticking it onto their 28-zoom to get a 140mm lens. Sadly, good teleconverters cost $400 or $500 and they only work opticallexpensive lenses. With a typical zoom lens, you'll get vignetting (darkening of the corners) when usinteleconverter.
Teleconverters are for professionals who own expensive lenses and want to save weight by not carrylenses. They are also useful sometimes with specialized tilt-shift lenses so that you don't have to buy in lots of different focal lengths.
Zoom lenses
Why carry around a whole bag of fixed focal length ("prime") lenses when you could just buy a Tam300 zoom lens for less than $400? With a twist of a ring, the Tamron will give you any focal length f28mm to 300mm. The only problem with this idea is that, sadly, the laws of physics and common sen
have not been repealed.
Photographic lenses in general are not very good. They only appear to be good because people very senlarge or closely inspect images. Camera lenses are subject to many kinds of distortion, all of whichmore difficult to reduce in a zoom lens design. Furthermore, zoom lenses tend to be slower (admit lethan prime lenses. This forces the photographer into using flash and/or a tripod.
Does that mean you shouldn't buy a zoom lens? Absolutely not. The average Canon EOS photographown three beautiful zoom lenses: Canon EF 16-35mm f/2.8L USM (review), Canon EF 24-70mm f/2USM (review), Canon EF 70-200mm f/2.8L IS USM (review). These are a great convenience for theand/or pressed-for-time photographer. However, none of these are as good as prime lenses in their folength range. Each of these zooms costs over $1000, so they won't help you out if you don't like the p
of the prime lenses.
If you can only have one lens, the Canon EF 24-70mm f/2.8L USM is probably better than the Canon50mm f/1.8 II, $93 (review). But the 50/1.8 is better than cheaper mid-range zooms.
Weird Camera Lens #1: The Fisheye
See our review of the Canon 15mm fisheye lens.
Weird Camera Lens #2: The Beyond 1:1 Macro lens
As far as I know, Canon is the only company in the world that makes a lens intended for convenientphotography of objects smaller than the film or digital sensor. See the photo.net review of the Canon65mm 1X-5X macro lens.
Be Careful (and rich)
Modern digital cameras produce extremely high quality images. In reasonable lighting conditions, thlimiting factor in the quality of your image will almost always be the lens. If you want to achieve a gresult, you must have the correct lens for the job and it must be a high quality example of that kind o
Lots of companies make high-quality lenses. Sadly, none of them have figured out how to break physlaws and do so cheaply. So if your creative goals require a long telephoto or very wide angle lens, prcough up the big bucks. If you are using a larger format than 35mm, prepare to cough up the big buckany lens!
Frequently Asked Questions regarding lensesby David Jacobson
This is the Lens FAQ. It is a technical document describing a lot of optics related information of use photographers and was originally published in the USENET rec-photo newsgroup. It does not answerquestions about particular commerical lenses. You won't find out whether Canon or Nikon is better. Bwill find all sorts of formulas and technical information.
Q1. What is the meaning of the symbols in the rest of this FAQ?
A. f - focal lengthSo - distance from front principal point to object (subject)
Sfar - distance from front principal point to farthest point in focusSclose - distance from front principal point to closest point in focusSi - distance from rear principal point to film (image) planeM - magnificationN - f-number or f-stopNe - effective f-number (corrected for bellows factor)c - diameter of largest acceptable circle of confusion, or the diameter of the circle of confusionh - hyperfocal distance* - the symbol for multiplication e.g. 3*4 means 3 times 4, which is equal to the number 12.^ - the symbol for exponentiation. e.g. 2^2 respresents 2 raised to the power of 2, i.e. 2 squared, and ito the number 4.
Here we use the more technical term "object" for the thing being focused on. Informally it is equivalethe subject. See technical notes [1] - [3] at the end for more information on object distances, moreinformation on the meaning of f-number and limitations to be observed when applying these formulalenses in which the aperture does not appear the same size front and rear.
Q2. What is the meaning of focal length? In other words, what
about a 50mm lens is 50mm?
A. A 50mm lens produces an image of a distant object on the film that is the same size as would be
produced by a pinhole 50mm from the film. See also Q5 below.
Q3. What is meant by f-stop?
A. The focal length of the lens divided by the diameter of the aperture (as seen from the front). It is acalled an f-number, and is written like f/8, which means the aperture diameter is 1/8th the focal lengt
The term is used both in regard to the maximum aperture of a lens and in regard to the aperture selecspecific situation.
The brightness of the image on the film is inversely proportional to the f-number squared. The depth increases but diffraction is worsened when using a large f-number. The effective f-number for all 3 echanges if the lens is focused extremely close. See Q7.
The term "stops" purportedly comes from old technology in which the aperture was selected by turniwheel with various sized holes in it, each one of which let in twice the light of the preceding one. Thuphrase "open up a N stops" means to change to an aperture allowing in 2^N times as much light, andconversely with "stop down N stops".
Q6. For a given lens and format what is angle of coverage?
A. If the format has a width, height, or diagonal of distance X, the angle of coverage along width, hediagonal is 2*arctan(X/(2*f*(M+1))). For example a 35mm frame is 24x36 mm, so with a 50 mm lendistant object (i.e. M virtually zero), the coverage is 27 degrees by 40 degrees, with a diagonal of 47degrees. See technical note [4] at the end for qualifications.
Q7. How do I correct for bellows factor?
A. Ne = N*(1+M)
Bellows factor is the factor by which the effective f-number gets multiplied as the lens is focused up See the technical notes.
Q8. What is meant by circle of confusion?
A. When a lens is defocused, a object point gets rendered as a small circle, called the circle of confus(Ignoring diffraction.) If the circle of confusion is small enough, the image will look sharp. There is ncircle "small enough" for all circumstances, but rather it depends on how much the image will be enl
the quality of the rest of the system, and even the subject. Nevertheless, for 35mm work c=.03mm isgenerally agreed on as the diameter of the acceptable circle of confusion. Another rule of thumb is c=of the diagonal of the frame, which comes to .025mm for 35mm film. (Zeiss and Sinar are known to bconsistent with this rule.)
A. The closest distance that is in acceptable focus when the lens is focused at infinity. (See below forvariant use of this term.)
h = f^2/(N*c)
Q10. What are the closest and farthest points that will be inacceptably sharp focus?
A. Sclose = h * So / (h + (So - f)) Sfar = h * So / (h - (So - f))
or, we can define a "hyperfocal ratio", hr = h/(So - f), or roughly the ratio of the hyperfocal distance tobject distance. Then
Sclose = So * hr/(hr+1) Sfar = So * hr/(hr-1)
These formulas are also correct when hr is defined as hr = h/So and the N used in computing h is actuNe.
If the denominator is zero or negative, Sfar is infinity.
Q11. What is depth of field?
A. It is convenient to think of a rear depth of field and a front depth of field. The rear depth of field idistance from the object to the farthest point that is sharp and the front depth of field is the distance fclosest point that is sharp to the object. Sometimes the term depth of field is used for the combinationthese two, i.e. the distance from the closest point that is sharp to the farthest point that is sharp.
In the last three, if the denominator is zero or negative, reardepth is infinity.
These formulas using hyperfocal distance can be used as follows. Suppose I know that the object distSo, is 1/8th of the hyperfocal distance. Then the range of distances that is acceptably sharp is from 8/to 8/7 of So. The front and rear depths of field are 1/9 So and 1/7 So.
A. It is a feature on higher quality SLR cameras that allows you to stop down the lens while looking the viewfinder. Ostensibly it allows you to "preview" the depth of field. Of course, since this stops doaperture, the image also gets dimmer.
Most people find it difficult to judge from a dim viewfinder image whether some part of the image wappear sharp in a slide or print. However, in many cases photographers will select a large aperture todeliberately blur background or foreground objects. DOF preview lets you see just what the effect wi
Q13. Where should I focus my lens so I will get everything from
some close point to infinity in focus?
A. At approximately the hyperfocal distance. More precisely, at So = h + f. In this condition the closepoint that will be in focus is at half the object distance. (Some authorities use this as the definition of
hyperfocal distance.)
Q14. Are there some simpler approximate formulas for depth o
field?
A. Yes. When the object distance is small with respect to the hyperfocal distance, the front and rear dfield are almost equal and depend only on the magnification and effective f-stop and the followingapproximate formulas can be used.
In non-macro situations Ne is the same as the marked f-number.
Q15. I have heard that one should use a long lens to get a shallo
depth of field and a short lens to get a large depth of field. Is thi
true?
A. Assuming that you frame the subject the same way, and that the object (subject) distance is small
compared with the hyperfocal distance for the shortest focal length being considered, the front and redepths of field are approximately equal and constant regardless of focal length. (See Question 14.)
However, there are two situations in which focal length does matter.
First, when the focal length is short enough, the hyperfocal distance, which varies with the square of focal length, will not be many times longer than the object distance, violating the condition above. In
case the front depth of field is smaller and the rear depth of field is larger, with the latter extending toabout when the hyperfocal distance is less than the object distance.
Second, the focal length of the lens also has a big effect on how fuzzy very distant points appear.Specifically, if the lens is focused on some nearby object rendered with magnification M, a point at i
will be rendered as a circle of diameter c, given by
c = f M / N
which shows that the distant background point will be fuzzed out in direct proportion to the focal leng(See the lens tutorial for some graphs that may make this more intuitive.)
Q16. If I focus on some point, and then recompose with that poi
not in the center, will the focus be off?
A. Yes, but maybe only a little bit. If the object is far enough away, the depth of field will cover the sdistance.
An approximate formula for the minimum distance such that the error will be covered by depth of fiegiven by
d = w^2/(2 N c)
where d = minimum distance to make the point be sharply rendered d is measured from the film plandistance image point on the film is from center of the image
For the 35mm format w^2/(2 c) is 5.4 meters, so you can recompose the image with the subject at theof the frame and still have it be sharp if the subject distance (at the center) was at least 5.4 meters (18divided by the f-number. See technical note [5] at the end for a bunch of assumptions.
Q17. If I get glasses (or bifocals) will my focusing be off?
A. No. The focusing screen is a diffusing plane in the same optical position as the film. If the image ion the focusing screen, it will also be sharp on the film. Many single lens reflex cameras have a split focusing aid. In effect one half causes the eye to see through the left side of the lens and the other halcauses the eye to see through the right side of the lens. Objects appear to be in the same position in bhalves only if the image plane coincides with the plane of the focusing screen and thus with film plan
hence are in sharp focus. All your glasses do is enable you to see the focusing screen or focusing aid
Q18. What are vignetting and light falloff?
A. Vignetting is a reduction in light falling on the film far from the center of the image that is causedphysical obstructions. Light falloff is a reduction of light far from the center because of fundamental reasons: First, an off-axis object sees a foreshortened apparent aperture (entrance pupil) so less light
collected. This results in a cos(theta) falloff, where theta is the angle off axis. Second, in a rectilinear the solid-angle-to-area magnification increases with cos^3(theta), spreading the light from a patch needge over more film than if the patch had been near the center. (The patch is presumed to face the cama constant very large distance.) As a result there is an overall cos^4(theta) falloff. The optical designecompensate for these effects by making the entrance pupil enlarge and tip when viewed from off the
axis. An alternative approach is to compensate by using a filter whose density varies appropriately wdistance from the center.
Q19. How can I tell if a lens has vignetting, or if a filter is causin
vignetting?
A. Open the back and, if necessary, trick the camera into opening the shutter and stopping down. Imaputting your eye right in the corner of the frame and looking at the diaphragm. Or course, you really this, so you have to move your head and sight through the corner of the frame, trying to imagine whatwould see. If you "see" the entire opening in the diaphragm and through it to object space, there is no
vignetting. However, at wide apertures in most lenses the edge of the rear element or the edge of the element or filter ring will obstruct your vision. This indicates vignetting. Try to estimate the fraction area of the diaphragm that is obstructed. Log base two of this fraction is the falloff in f-stops at the co
You can also do this from the front. With SLRs hold the camera a fair distance away with a fairly brigarea behind the viewfinder hole. With non-SLRs open the back and arrange so a reasonably bright arbehind the camera. Look through the lens, and rotate the camera until you are looking right at one cothe viewing screen or frame. (If you are using the mirror-down technique with an SLR, choose an upcorner of the frame, i.e. look from below the axis.) Now for the hard part. Look at the aperture you sethere is vignetting you see something about the shape of an American football. If the filter is causingvignetting, one of the edges of the football is formed by the filter ring.
A third way to detect vignetting is to aim the camera at a small bright spot surrounded by a fairly darbackground. (A distant street light at night would serve well.) Deliberately defocus the image some aobserve the shape of the spot, particularly in the corners. If it is round there is no vignetting. If it lookthe intersection of some arcs (i.e. like an American football), then there is vignetting. Note that near tthe image the top of the circle may get clipped a bit. This is because in many cameras some light (frotop part of the image) misses the bottom of the mirror. This affects only the viewfinder, not the film. can use depth of field preview (if your camera has it) to determine the f-stop at which the spot becomround. With wide-angle lenses the circle of confusion may not get large enough for this technique to useful.
Q20. For panoramic pictures, where is the best place to pivot thcamera?
A. The axis of the pivot should pass through the entrance pupil. The entrance pupil is the virtual imagthe aperture as seen through the front of the lens.
When you've got it right, the entrance pupil will not shift relative to fixed objects as you rotate the ca(Stop down the lens so you can see the diaphragm and aperture.)
There is a whole different type of panoramic camera in which the lens is rotated relative to the film. Itype of camera the lens rotates around the rear nodal point (for objects at infinity). See the lens tutori
an explanation of nodal points.
Q21. What is diffraction?
A. When a beam of light passes through any aperture it spreads out. This effect limits how sharp a lepossibly be.
The diffraction is caused by the limiting of the beam to the size of the aperture, not primarily by sharof the aperture. Even if one made a "soft edged" aperture that faded slowly from clear to opaque, therwould still be diffraction, and the size of the central part of the diffraction pattern would not change mcompared with the sharp-edged case.
Q22. What is the diffraction limit of a lens.
A. All lenses are diffraction limited to no more than about 1500/N to 1800/N line pairs per mm. See bunder the question 27 - "What is MTF?".
Q23. What are aberrations?
A. Aberrations are image defects that result from limitations in the way lenses can be designed. Bettelenses have smaller aberrations, but aberrations can never be completely eliminated, just reduced.
The classic aberrations are:
• Spherical aberration. Light passing through the edge of the lens is focused at a different distan(closer in simple lenses) than light striking the lens near the center.• Coma. Off axis points are rendered with tails, reminiscent of comets, hence the name. It can bshown that coma must occur if the image formed by rays passing near the edge of the lens has a diffemagnification than the image formed by rays passing near the center of the lens.• Astigmatism. Off-axis points are blurred in their the radial or tangential direction, and focusinreduce one at the expense of the other, but cannot bring both into focus at the same time. Think of it focal length as varying around the circumference of the lens. (Optometrists apply the word "astigmat
a defect in the human eye that causes on-axis points to be similarly blurred. That astigmatism is not qsame as astigmatism in photographic lenses.)• Curvature of field. Points in a plane get focused sharply on a curved surface, rather than a plafilm). Or equivalently, the set of points in the object space that are brought to sharp focus on the film form a curved surface rather than a plane. With a plane subject or a subject at infinite distance the neis that when the center is in focus the edges are out of focus, and if the edges are in focus the center ifocus.
• Distortion (pincushion and barrel). The image of a square object has sides that curve in or outshould not be confused with the natural perspective effects that become particularly noticeable with wangle lenses.) This happens because the magnification is not a constant, but rather varies with the angfrom the axis.• Chromatic aberration. The position (forward and back) of sharp focus varies with the wavelen•
Lateral color. The magnification varies with wavelength.
Q24. Can I eliminate these aberrations by stopping down the le
A. The effect of all aberrations except distortion and lateral color is reduced by stopping down. The aof field curvature is not affected by stopping down, but its effect on the film is. But note that stoppingalso increases diffraction.
Q25. Why do objects look distorted when photographed with a
angle lens?
A. This is because the size of the image of an object depends on the distance the object is from the leis not a defect in the lens---even pinhole cameras with no lens at all exhibit this perspective effect.
For image calculation purposes, think of the lens as being a pinhole one focal length in front of the ficentered over the center of the film. (If the lens is not focussed at infinity, the distance from the film somewhat larger.) Then the image of an object point can be found by drawing a straight line from thepoint through the pinhole and finding its intersection with the film. That line represents one light ray.(Diffraction and out-of-focus conditions have been ignored here, since they are irrelevant to this effe
If you do this, you'll find that the image of a nearby object will be larger than the image of the same o
farther away, by the ratio of the distances. You'll also find that any straight line in object space, no mwhat angle or position, will be rendered as a straight line on the film. (Proof outline: a line, and a poion the line define a plane. All rays from the object line will stay in the plane defined by the line and tpinhole, and the intersection of that plane with the film plane is a straight line.) But parallel lines in ospace are not necessarily parallel on the film.
Q26. How does focal length affect perspective?
A. It doesn't; it is subject distance that affects perspective. However, a longer lens provides more submagnification at a given distance, so you can get farther from your subject without having the image
small. By moving back, you make the magnification ratio between the front and back of your subjectsmaller, because the distance ratio is closer to one. So, in a portrait, instead of a nose that's magnifiedmore than the rest of the head, the nose is magnified only very slightly more than the rest of the headthe picture looks more pleasing.
You can get the same perspective with a shorter focal length lens by simply moving back, and enlargcentral portion of the image. Of course, this magnifies grain as well, so it's better to use a longer lenshave one.
A. MTF is an abbreviation for Modulation Transfer Function. It is the normalized spatial frequencyresponse of film or an optical system. The spatial frequency is usually measured in cycles per millimFor an ideal lens and ignoring diffraction, the MTF would be a constant 1 at all spatial frequencies. F
practical lenses lenses, the MTF starts out near 1 and falls off at increasing frequencies. MTFs vary waperture, the distance the image region is from the center, the direction of the pattern (along a radius degrees to that), the wavelength of the light, and the subject distance.
Even for an ideal lens, diffraction effects fundamentally force the MTF be be zero at spatial frequencbeyond 1/(lambda*N) cycles per mm, where lambda is the wavelength of the light. For lambda = 555the peak of the eye's response, this is very close to 1800/N cycles per mm.
The MTF of a system is the product of the properly scaled MTFs of each of its components, as long aare not two consecutive non-diffusing components. (Thus with proper scaling you can multiply cameMTF by film MTF by enlarger lens MTF by paper MTF, but usually not a telescope objective MTF b
eyepiece MTF. There are also some other obscure conditions under which MTFs can be multiplied.)
Note that although MTF is usually thought of as the spatial frequency response function and is plottespatial frequency as the abscissa, some manufacturers (e.g. Canon) publish plots of the MTF at specifspatial frequencies with distance from the center of the image as the abscissa.
Q28. What is SQF?
SQF is an abbreviation for Subjective Quality Factor. SQF was developed by Ed Grainger of EastmaKodak as an objective measurement that correlated well with subjective rankings of print quality. So
simplified, it is just the MTF in the print (or referred to a designated print size or magnification) averfrom .5 to 2 cycles per mm. See technical note [6]. One well-known popular magazine reports lens teresults in terms of what they claim to be SQF, but they apparently use some other definition of SQF, showing Ed Grainger's picture and referring readers to his original SQF paper.
Q29. What are "elements" and "groups", and are more better?
A. The number of elements is the number of pieces of glass used in the lens. Single uncemented elemtwo or more elements cemented together are called a group. Thus a lens that has 8 elements in 7 grou8 pieces of glass with 2 cemented together. It is impossible to completely correct all aberrations. Eacadditional element the designer has at his/her disposal gives a few more degrees of freedom to design
aberration. So one would expect a 6 element lens to be better than a 3 element lens. However, each sualso reflects a little light, causing flare. So too many elements is not good either. Note that an unscrupmanufacturer could slap together 13 pieces of glass and claim to have a 13 element lens, but it mightterrible. So by itself the number of elements is no guarantee of quality.
A. Low dispersion glass is specially formulated to have a small variation of index of refraction withwavelength. This makes it easier for the designer to reduce chromatic aberration and lateral color. Thof glass is most often used in long lenses. Marketing designators such as ED and SLD hint at the use dispersion glass.
Q31. What do APO and Apochromatic mean?
A. The distance behind the lens at which monochromatic light (light of a single wavelength) comes tovaries as a smooth function of the wavelength. If this function has a zero derivative in the visible ranhence if there are two wavelengths at which the light comes to focus in the same plane, the lens is caachromatic. If there is a higher order correction, usually with the result that 3 or more visible wavelencome to focus at the same distance, the lens is called apochromatic. Some authorities add more condiApochromatic lenses often contain special low-dispersion glasses. APO is an abbreviation for apochr
Q32. What is an "aspheric element"?
A. It a lens element in which the radius of curvature varies slightly with angle off axis. Aspheric elemgive the lens designer more degrees of freedom with which to correct aberrations. They are most oftein wide angle and zoom lenses.
Q33. What is a teleconverter?
A. A teleconverter is a device that enlarges the center portion of the normal frame to fill the whole fr35mm systems where the frames are 24x36 millimeters, a 2X teleconverter expands the central 12x1to fill the full 24x36mm frame.
Q34. How does a teleconverter affect exposure, focusing, depth field and image quality?
A. A lens of focal length f and f-number N with a teleconverter of magnification K attached will behall respects like a lens of focal length K*f and f_number K*N.
If the aperture diameter and focus are left untouched and an ideal teleconverter is attached, the lens wfocus at the same distance, the image, including the diffraction effects and lens aberration effects, witimes as large, the exposure will need to be K^2 times longer, the hyperfocal distance will be multiplK and the depth of field will be divided by K. A practical teleconverter will also contribute some of i
aberrations. (See technical note [7].)
On the other hand, if you open the aperture to keep the same effective f-number and hence the sameexposure time, the image will be enlarged by K, the diffraction will be unchanged, the depth of field divided by K^2 and the hyperfocal distance multiplied by K^2. The aberrations are increased by threeffects: the lens is opened to a larger aperture, the teleconverter multiplies those (probably larger)aberrations by K, and then combines them with some of its own.
Since the focusing is unchanged, the minimum focusing distance is the same whether or not a teleconis attached. (See technical note - [8].)
Q35. What is the difference between using a teleconverter at th
time the picture is exposed vs. enlarging more in the printingprocess?
A. Assuming the aperture diameter is the same in the two cases, the teleconverter case will require Ktimes the exposure while the enlarging case will enlarge the grain in the film K times as much. Theteleconverter adds some aberrations of its own, while enlarging more will make aberrations in the enlens more apparent. All other effects are identical. In 35mm format, grain is usually the dominate facimage quality.
Q36. How can I take "close up" pictures.
A. There are several ways.
• Use a true macro lens.• Move the lens farther from the film with extension tubes or bellows.• Screw on "diopter lenses" or closeup "filters".• Use the macro setting on many zoom lenses.
A true macro lens generally gives the best quality. The f-number needs to be corrected according to tformulas above, unless metering is done through the lens. Most macro lenses go from infinity to 1:1 o(mag = 1 or 1/2). Some that go to 1:2 come with an accessory screw-on lens that gets to 1:1.
Extension tubes and bellows move the lens farther from the film, allowing it to focus closer. All lensoptimized for specific situations, and using extension tubes or bellows makes the lens operate out of region for which it was designed, possibly compromising the quality a bit. You can compute themagnification from the extension using the formulas above. If the magnification exceeds one, it is bereverse the lens with an adapter. Extending the lens also changes the effective f-number. See the formabove. However, if you meter through the lens, the meter is affected in exactly the same way, so youneed to do any calculation. Lenses on some modern electronic cameras require electrical connectionsbody, complicating the construction of these devices.
Add-on lenses shorten the effective focal length of the lens and reduce the working distance. Single e
add-on lenses are of inadequate quality for critical work. Many photographers report good results usielement lenses at small apertures. No correction is required to the effective f-number.
Some zoom lenses have special macro ranges. However, few zoom lenses get larger magnification thand in many lenses the macro feature operates only at the short focal length end of the zoom. This is really serious work.
If you are photographing flat objects, such as postage stamps, freedom from distortion is important, areasonably flat field.
Working distance is the distance from the front of the lens to the subject at a particular magnificationnature work, a reasonably long working distance is important because working farther away is less li
frighten insects, etc., and shadows are less likely to fall on the subject.
Q37: What is the optimum aperture for a pinhole camera?
A. d = .036 sqrt(Si), where d is the diameter of the pinhole in millimeters and Si is the distance from pinhole to the film in millimeters. See technical note [9].
Q38. How can I use my photographic light meter or camera to
measure illumination?
A. Take an exposure reading with an incident meter or a reflected meter pointed at an 18% gray subj(gray card). (Meters built into cameras are reflected meters. If the lens is a variable aperture zoom, beis zoomed to where the aperture reading is correct. Turn off special intelligent or evaluative meteringmodes.) Then use one of the following formulas, where E is illuminance.
• E_in_foot_candles = 25 N^2 / (ISO * exposure_time_in_seconds)• E_in_lux = 269 N^2 / (ISO * exposure_time_in_seconds)
See technical note [10].
More Questions?If this document doesn't answer your questions, there are additional resources on photo.net:
[1] - The object distance, So, as used in the formulas is measured from the object to the lens's front ppoint. More commonly one hears of the front nodal point. These two points are equivalent if the fronmedium and rear medium are the same, e.g. air. They are the effective position of the lens for measurto the front. In a simple lens the front nodal/principal point is very near the center of the lens. If you kthe focal length of the lens, you can easily find the front nodal point by taking the lens off the cameraforming an image of a distant object with the light going through the lens backwards. Find the point focus, then measure one focal length back (i.e. toward the distant object). That is the position of the fnodal point.
[2] - On most cameras the focusing scale is calibrated to read the distance from the object to the film There is no easy way to precisely convert between the focusing scale distance and So.
[3] - The formulas presented here all assume that the aperture looks the same size front and rear. If itnot, use the front diameter and note that the formulas for bellows correction and depth of field will no
correct at macro distances. Formulas for this situation are given in the lens tutorial, posted separately
[4] - The formula for angle of coverage applies to rectilinear lenses. An alternative form, 2*arctan(X(2*Si)), applies to both rectilinear lenses and pinholes. (Rectilinear lenses give the same projection aspinhole.) These formulas do not usually apply to fisheye lenses, and can't possibly apply to a fisheye that covers 180 degrees or more.
[5] - The conditions under which the formula for the minimum distance at which the effect of focusinre-composing will be covered by depth of field are:
1. w is no more than the focal length of the lens. At the edge w=18mm for 35mm, so this will ve
seldom be a problem.2. The lens's two nodal points are not very widely separated. But if the front nodal point is in frothe rear nodal point, which I think is the more common case, the formula is too conservative, so this problem either.3. The camera is rotated about the front nodal point. Almost always the camera will be rotated aaxis behind the front nodal point which again makes the formula too conservative. The guide numberassumes c=.03mm.
[6] - The SQF is the weighted average of the MTF over the range .5 to 2 lines per mm referred to adesignated print size or magnification. The weighting function is 1/spf, where spf is the spatial frequeturns out that this is equivalent to just a simple "visual" average when the MTF is plotted against the
the spatial frequency. A further mean is taken between the the saggital (optics-speak for radial) andtangential components. It appears to this author that an additional, probably weighted, averaging musdone over regions of the image (center, edges, corners). When I find out the specifics of this weightinadd it to the lens FAQ.
[7] - Note that the section on teleconverters in several places assumed that the aperture diameter was unchanged. On lenses with mechanical aperture setting levers or rings this will happen naturally if thaperture setting is not changed. However, beware that fancy electronic cameras may compensate for presence of the teleconverter.
[8] - Most camera systems have focusing scales that read from some reference mark on the body, usu
the film plane. With a teleconverer attached, they read from a point the thickness of the teleconverterfront of this reference mark.
[9] - The optimum aperture for a pinhole camera depends on what criteria is used. The formula givenmaximizes the spatial frequency at which the MTF for 555nm light will be 20%.
[10] - There is no universal agreement on the constant in the relation between exposure, film speed, aillumination. This document tentatively shows 25 for the foot-candles case, which I reverse engineer
a Gossen Lunasix meter, but one can find values from 18 to 30 in the literature or by reverse engineeother meters. The constant for lux is 10.7639 (the number of square feet in a square meter) times the for foot-candles.
This note gives a tutorial on lenses and gives some common lens formulas. I attempted to make it betan FAQ (just simple facts) and a textbook. I generally give the starting point of an idea, and then skipresults, leaving out all the algebra. If any part of it is too detailed, just skip ahead to the result and go
The theory is simplified to that for lenses with the same medium (e.g. air) front and rear: the theory funderwater or oil immersion lenses is a bit more complicated.
Depth of Field • Diffraction • Modulation Transfer Function (MTF) • Illumination (by John Bercovitz)
Part I - Object distance, image distance, and magnification
Throughout this article we use the word "object" to mean the thing of which an image is being made.loosely equivalent to the word "subject" as used by photographers.
In lens formulas it is convenient to measure distances from a set of points called "principal points". T
are two of them, one for the front of the lens and one for the rear, more properly called the primary ppoint and the secondary principal point. While most lens formulas expect the object distance to be mfrom the front principal point, most focusing scales are calibrated to read the distance from the objecfilm plane. So you can't use the distance on your focusing scale in most calculations, unless you only an approximate distance. Another interpretation of principal points is that a (probably virtual) object primary principal point formed by light entering from the front will appear from the rear to form a (pvirtual) erect image at the secondary principal point with magnification exactly one.
"Nodal points" are the two points such that a light ray entering the front of the lens and headed straigtoward the front nodal point will emerge going straight away from the rear nodal point at exactly the angle to the lens's axis as the entering ray had. The nodal points are identical to the principal points wthe front and rear media are the same, e.g. air, so for most practical purposes the terms can be usedinterchangeably.
In simple double convex lenses the two principal points are somewhere inside the lens (actually 1/n-tway from the surface to the center, where n is the index of refraction), but in a complex lens they canalmost anywhere, including outside the lens, or with the rear principal point in front of the front princpoint. In a lens with elements that are fixed relative to each other, the principal points are fixed relatithe glass. In zoom or internal focusing lenses the principal points generally move relative to the glasseach other when zooming or focusing.
When a camera lens is focused at infinity, the rear principal point is exactly one focal length in fronfilm. To find the front principal point, take the lens off the camera and let light from a distant object pthrough it "backwards". Find the point where the image is formed, and measure toward the lens one f
length. With some lenses, particularly ultra wides, you can't do this, since the image is not formed in the front element. (This all assumes that you know the focal length. I suppose you can trust themanufacturer's numbers enough for educational purposes.)
So object to front principal point distance.Si rear principal point to image distancef focal lengthM magnification
If we interpret Si-f as the "extension" of the lens beyond infinity focus, then we see that this extens
inversely proportional to a similar "extension" of the object.
Ray Tracing
For rays close to and nearly parallel to the axis (these are called "paraxial" rays) we can approximatemodel most lenses with just two planes perpendicular to the optic axis and located at the principal poi"Nearly parallel" means that for the angles involved, theta ~= sin(theta) ~= tan(theta
means approximately equal.) These planes are called principal planes.
The light can be thought of as proceeding to the front principal plane, then jumping to a point in the rprincipal plane exactly the same displacement from the axis and simultaneously being refracted (bentangle of refraction is proportional the distance from the center at which the ray strikes the plane andinversely proportional to the focal length of the lens. (The "front principal plane" is the one associatedthe front of the lens. It could be behind the rear principal plane.)
Let us define an ideal lens as one that forms undistorted sharp images of an object plane on an imageSuch an ideal lens is only possible for a specified set of planes. A ray from an object point in the spec
object plane and passing through the front nodal point exits the rear nodal point a the same angle andthrough the image point. All rays passing through the object point also pass though the image point. Texiting ray can be computed by the following technique. Consider a spherical surface centered on thepoint and of such radius that the front principal point is in the surface. Consider a second surface cenon the image point and of such radius that the rear principal point is in the surface. Any ray through t
object point can be considered to proceed to the first surface, then jump parallel to the axis to the secsurface (backwards if necessary), and from there proceed to the image point. Only the first and lastcomponents contribute to the optical path length.
Part II - Apertures, f-stop, bellows correction factor, pupil
magnification
We define more symbols
D diameter of the entrance pupil, i.e. diameter of the aperture asseen from the front of the lens
N f-number (or f-stop) D = f/N, as in f/5.6Ne effective f-number, based on geometric factors, but not absorptio
Light from an object point spreads out in a cone whose base is the entrance pupil. (The lens elementsfront of the diaphragm form a virtual image of the physical aperture. This virtual image is called theentrance pupil.)
Analogous to the entrance pupil is the exit pupil, which is the virtual image of the aperture as seen thothe rear elements.
Let us define Ne, the effective f-number, as
Ne = 1/(2 sin(thetaX))
where thetaX is the angle from the axis to the edge of the eXit pupil as viewed from the film plane. Itshown that for any lens free of coma the following also holds
Ne = M/(2 sin(thetaE)).
We will ignore the issue of coma throughout the rest of this document.
The first equation deals with rays converging to the image point, and is the basis for depth of field
calculations. The second equation deals with light captured by the aperture, and is the basis for exposcalculations.
This section will explain the connection between Ne and light striking the film, relate this to N, and s
compute Ne for macro situations.
If an object radiated or reflected light uniformly in all directions, it is clear that the amount of light caby the aperture would be proportional to the solid angle subtended by the aperture from the object po
optical theory, however, it is common assume that the light follows Lambert's law, which says that thintensity falls off with cos(theta), where theta is the angle off the normal. With this assumptio
can be shown that the light entering the aperture from a point near the axis is proportional tosin^2(thetaE), which is proportional to the aperture area for small thetaE.
If the magnification is M, the light from a tiny object patch of unit area gets spread out over an area Mthe film, and so the relative intensity on the film is inversely proportional to M^2. Thus the relative in
on the film, RI, is given by
RI = sin^2(thetaE)/M^2 = 1/(4 Ne^2)
with the second equality by the defintion of Ne. (Of course the true intensity depends on the subject
illumination, etc.)
For So very large with respect to f, M is approximately f/So and sin(thetaE) is approximately
(D/2)/So. Substituting these into the above formula get that RI = ((D/2)/f)^2 = 1/(4N^
thus for So >> f,
Ne = D/f = N.
For closer subjects, we need a more detailed analysis. We will take D = f/N as determining D,
Let us go back to the original approximate formula for the relative intensity on the film, and substitutcarefully
RI = sin^2(thetaE)/M^2 = ((D/2)^2/((D/2)^2+(So-zE)^2))/M^2
where zE
is the distance the entrance pupil is in front of the front principal point.
However, zE is not convenient to measure. It is more convenient to use "pupil magnification". The p
magnification is the ratio of exit pupil diameter to the entrance pupil diameter.
p pupil magnification (exit_pupil_diameter/entrance_pupil_diameter)
For all symmetrical lenses and most normal lenses the aperture appears the same from front and rear,p~=1. Wide angle lenses frequently have p>1. It can be shown that zE = f*(1-1/p), and substi
this into the above equation, carrying out some algebraic manipulations, and solving with RI = 1/Ne^2) yields
Ne = Sqrt((M/2)^2 + (N*(1+M/p))^2).
If we further assume thetaE is small enough that sin(thetaE) ~= tan(thetaE), the (M/2
This is the standard equation, and will be used throughout the rest of this document. The essence of thapproximation is the distinction between the axial distance to the plane of the entrance pupil and thedistance along the hypotnuse to the edge of the entrance pupil, which is the really correct form. Cleartypical photographic sitations that distinction is insignificant.
An alternative, but less fundamental, derivation is based on the relative illumination varying with theinverse square of the distance from the exit pupil to the film. This distance is just f*(1+M) - zX,
zX is the distance the exit pupil is behind the rear principal point. It can be shown that zX = -f*(p
so Ne/N = (f*(1+M)+f*(p-1))/(f+f*(p-1)) = 1+M/p, and hence Ne = N*(1+M/p
It is convenient to think of the correction in terms of f-stops (powers of two). The correction in powetwo (stops) is 2*Log2(1+M/p) = 6.64386 Log10(1+M/p). Note that for most normal lense
so the M/p can be replaced by just M in the above equations.
Part III - Circle of confusion, depth of field and hyperfocaldistance.
The light from a single object point passing through the aperture is converged by the lens into a coneits tip at the film (if the point is perfectly in focus) or slightly in front of or behind the film (if the objpoint is somewhat out of focus). In the out of focus case the point is rendered as a circle where the filthe converging cone or the diverging cone on the other side of the image point. This circle is called thcircle of confusion. The farther the tip of the cone, ie the image point, is away from the film, the largcircle of confusion.
Consider the situation of a "main object" that is perfectly in focus, and an "alternate object point" thisfront of or behind the main object.
Soa alternate object point to front principal point distanceSia rear principal point to alternate image point distanceh hyperfocal distanceC diameter of circle of confusionc diameter of largest acceptable circle of confusionN f-stop (focal length divided by diameter of entrance pupil)Ne effective f-stop Ne = N * (1+M/p)D the aperture (entrance pupil) diameter (D=f/N)M magnification (M=f/(So-f))
The diameter of the circle of confusion can be computed by similar triangles, and then solved in termlens parameters and object distances. For a while let us assume unity pupil magnification, i.e. p=1. W
Note that in this formula C is positive when the alternate image point is behind the film (i.e. the altern
object point is in front of the main object) and negative in the opposite case. In reality, the circle of confusion is always positive and has a diameter equal to Abs(C).
If the circle of confusion is small enough, given the magnification in printing or projection, the opticquality throughout the system, etc., the image will appear to be sharp. Although there is no one diammarks the boundary between fuzzy and clear, .03 mm is generally used in 35mm work as the diameteacceptable circle of confusion. (I arrived at this by observing the depth of field scales or charts on/winumber of lenses from Nikon, Pentax, Sigma, and Zeiss. All but the Zeiss lens came out around .03mZeiss lens appeared to be based on .025 mm.) Call this diameter c.
If the lens is focused at infinity (so the rear principal point to film distance equals the focal length), thdistance to closest point that will be acceptably rendered is called the hyperfocal distance.
h = f^2/(N*c)
If the main object is at a finite distance, the closest alternative point that is acceptably rendered is at d
Sclose = h So/(h + (So-F))
and the farthest alternative point that is acceptably rendered is at distance
Sfar = h So/(h - (So - F))
except that if the denominator is zero or negative, Sfar = infinity.
We call Sfar-So the rear depth of field and So-Sclose the front depth field.
A form that is exact, even when P != 1, is
depth of field = c Ne / (M^2 * (1 +/- (So-f)/h1))= c N (1+M/p) / (M^2 * (1 +/- (N c)/(f M))
where h1 = f^2/(N c), ie the hyperfocal distance given c, N, and f and assuming P=1. Use + f
depth of field and - for rear depth of field. If the denominator goes zero or negative, the rear depth ofinfinity. (!= means "is not equal to".)
This is a very nice equation. It shows that for distances short with respect to the hyperfocal distance, depth of field is very close to just c*Ne/M^2. As the distance increases, the rear depth of field gets l
than the front depth of field. The rear depth of field is twice the front depth of field when So-f is on
the hyperfocal distance. And when So-f = h1, the rear depth of field extends to infinity.
If we frame an object the same way with two different lenses, i.e. M is the same both situations, the sfocal length lens will have less front depth of field and more rear depth of field at the same effective f(To a first approximation, the depth of field is the same in both cases.)
Another important consideration when choosing a lens focal length is how a distant background poinbe rendered. Points at infinity are rendered as circles of size
C = f M / N
So at constant object magnification a distant background point will be blurred in direct proportion to focal length.
This is illustrated by the following example, in which lenses of 50mm (red) and 100 mm (green) focalengths are both set up to get a magnification of 1/10. Both lenses are set to f/8. The graph shows theof confusions as a function of the distance behind the object.
The slope of both graphs virtually identical out to well beyond where the diameter of the cirlce of consfusion is .03mm, showing that to a first approximation both lenses have the same depth of field.However, the size of the circle of confusion for in infinitely distant point is twice as large for the 100lens (1.25mm) as for the 50mm lens (.625mm).
Part IV - DiffractionWhen a beam of parallel light passes through a circular aperture it spreads out a little, a phenomenonas diffraction. The smaller the aperture, the more the spreading. The normalized field strength (of theelectric or magnetic field) at angle phi from the axis is given by
and where R is the radius of the aperture, lambda is the wavelength of the light, and J1 is the first o
Bessel function. The normalization is relative to the field strength at the center. The power (intensity)proportional to the square of this function.
The field strength function forms a bell-shaped curve, but unlike the classic E^(-x^2) one, it event
oscillates about zero. Its first zero is at 1.21967 lambda/(2 R). There are actually an infinite nof lobes after this, but about 83.8% of the power is in the circle bounded by the first zero.
Approximating the aperture-to-film distance as f and making use of the fact that the aperture has dia
f/N, it follows directly that the diameter of the first zero of the diffraction pattern is
2.43934*N*lambda. Applying this in a normal photographic situation is difficult, since the light
contains a whole spectrum of colors. We really need to integrate over the visible spectrum. The eye hmaximum sensitivity around 555 nm, in the yellow green. If, for simplicity, we take 555 nm as thewavelength , the diameter of the first zero, in mm, comes out to be 0.00135383 N.
As was mentioned above, the normally accepted circle of confusion for depth of field is .03 mm, but
03/0.00135383 = 22.1594, so we can see that at f/22 the diameter of the first zero of the diffraction pas large is the acceptable circle of confusion.
A common way of rating the resolution of a lens is in line pairs per mm. It is hard to say when lines aresolvable, but suppose that we use a criterion that the center of a dark band receive no more than 80the light power striking the center of a light band. Then the resolution is 0.823 /(lambda*N) lp
we again assume 555 nm, this comes out to 1482/N lpmm, which is in close agreement with the wid
used rule of thumb that the resolution is diffraction limited to 1500/N lpmm. However, note that the
discussed below, provides another view of this subject.
Part V - Modulation Transfer Function
The modulation transfer function is a measure of the extent to which a lens, film, etc., can reproduce in an image. It is the spatial analog of frequency response in an electrical system. The exact definitiothe modulation transfer function and of the related optical transfer function vary slightly amongst difauthorities.
The 2-dimensional Fourier transform of the point spread function is known as the optical transfer fun(OTF). The value of this function along any radius is the fourier transform of the line spread functionsame direction. The modulation transfer function is the absolute value of the fourier transform of the spread function.
Equivalently, the modulation transfer function of a lens is the ratio of relative image contrast divided
relative object contrast of an object with sinusoidally varying brightness as a function of spatial frequ(e.g. cycles per mm). Relative contrast is defined as (Imax-Imin)/(Imax+Imin). MTF can als
used for film, but since film has a non-linear characteristic curve, the density is first transformed backequivalent intensity by applying the inverse of the characteristic curve.
For a lens, the MTF can vary with almost every conceivable parameter, including f-stop, object distadistance of the point from the center, direction of modulation, and spectral distribution of the light. Tstandard directions are radial (also known as sagittal) and tangential.
The MTF for an an ideal lens (ignoring the unavoidable effect of diffraction) is a constant 1 for spatiafrequencies from 0 to infinity at every point and direction. For a practical lens it starts out near 1, and
off with increasing spatial frequency, with the falloff being worse at the edges than at the center. Adjeffects in film can make the MTF of film be greater than 1 in certain frequency ranges.
An advantage of the MTF as a measure of performance is that under some circumstances the MTF ofsystem is the product (frequency by frequency) of the properly scaled MTFs of its components. Suchmultiplication is always allowed when the phase of the waves is lost at each step. Thus it is legitimatmultiply lens and film MTFs or the MTFs of a two lens system with a diffuser in the middle. HoweveMTFs of cascaded ordinary lenses can legitimately be multiplied only when a set of quite restrictive atechnical conditions is satisfied.
Let lambda be the wavelength of the light, and spf the spatial frequency in cycles per mm.
For pure diffraction the formula is
OTF(lambda,N,spf) = 2/Pi (ArcCos(lambda N spf) - lambda N spf Sqrt(1-(lamspf)^2))
Note that for lambda = 555 nm, the OTF is zero at spatial frequencies of 1801/N cycles per mm
beyond.
For a diffraction-free circle of confusion of diameter C,
OTF(C,spf) = 2 J1(Pi C spf)/(Pi C spf)
where, again, J1(x) is the first order Bessel function. The OTF goes negative at certain frequencies
Physically, this would mean that if the test pattern were lighter right on the optical center than nearbyimage would be darker right on the optical center than nearby. Some authorities use the term "spuriouresolution" for spatial frequencies beyond the first zero. The MTF is the absolute value of the OTF.
For the case where there is a combination of diffraction and focus error dz (resulting in a circle of co
of diamter dz/N), the OTF is given by the following formula, which involves an integration that mu
done numerically. Let s = lambda N spf, and a = Pi spf dz / N.
OTF = 4/(Pi a) integral y=0 to sqrt(1-s^2) of sin(a(sqrt(1-y^2)-s)) dyfor s < 10 for s >= 1
This formula is an approximation that is best at small apertures.
Here is a graph of the OTF of the f/22 diffraction limit, a .03mm circle of confusion assuming nodiffraction, and the combined effect.
Note how the combination is not the product of each of the effects taken separately.
should be multiplied by 4/3 to get the candles coming off perpendicular to the lamp filament. Incidenthe number of lumens coming from an incandescent lamp varies approximately as the 3.6 power of thvoltage. This can be really important if you are using a lamp of known candlepower to calibrate aphotometer.
Illumination (illuminance), E, is the _areal density_ of incident luminous flux: how many lumens perarea. A lumen per square foot is a foot-candle; a one square foot area on the surface of a sphere of raone foot and having a one candle point source centered in it would therefore have an illumination of foot-candle due to the one lumen falling on it. If you substitute meter for foot you have a meter-candlux. In this case you still have the flux of one steradian but now it's spread out over one square meterMultiply an illumination level in lux by .0929 to convert it to foot-candles. (foot/meter)^2= .0929. Acentimeter- candle is a phot. Illumination from a point source falls off as the square of the distance. Syou divide the intensity of a point source in candles by the distance from it in feet squared, you have tillumination in foot candles at that distance.
Luminance, B, is the _areal intensity_ of an extended diffuse source or an extended diffuse reflector.
perfectly diffuse, perfectly reflecting surface has one foot-candle (one lumen per square foot) of illumination falling on it, its luminance is one foot-Lambert or 1/pi candles per square foot. The totalamount of flux coming off this perfectly diffuse, perfectly reflecting surface is, of course, one lumen square foot. Looking at it another way, if you have a one square foot diffuse source that has a luminaone candle per square foot (pi times as much intensity as in the previous example), then the total outpthis source is pi lumens. If you travel out a good distance along the normal to the center of this one sqfoot surface, it will look like a point source with an intensity of one candle.
To contrast: Intensity in candles is for a point source while luminance in candles per square foot is foextended source - luminance is intensity per unit area. If it's a perfectly diffuse but not perfectly reflesurface, you have to multiply by the reflectance, k, to find the luminance.
Also to contrast: Illumination, E, is for the incident or incoming flux's areal _density_; luminance, B,reflected or outgoing flux's areal _intensity_.
Lambert's law says that an perfectly diffuse surface or extended source reflects or emits light accordicosine law: the amount of flux emitted per unit surface area is proportional to the cosine of the anglebetween the direction in which the flux is being emitted and the normal to the emitting surface. (Notehowever, that there is no fundamental physics behind Lambert's "law". While assuming it to be truesimplifies the theory, it is really only an empirical observation whose accuracy varies from surface tosurface. Lambert's law can be taken as a definition of a perfectly diffuse surface.)
A consequence of Lambert's law is that no matter from what direction you look at a perfectly diffusesurface, the luminance on the basis of _projected_ area is the same. So if you have a light meter lookperfectly diffuse surface, it doesn't matter what the angle between the axis of the light meter and the nto the surface is as long as all the light meter can see is the surface: in any case the reading will be th
There are a number of luminance units, but they are in categories: two of the categories are those usinEnglish units and those using metric units. Another two categories are those which have the constant
built into them and those that do not. The latter stems from the fact that the formula to calculate lumi(photometric Brightness), B, from illumination (illuminance), E, contains the factor 1/pi. To illustrate
B = (k*E)(1/pi)Bfl = k*E
where: B = luminance, candles/foot^2Bfl = luminance, foot-Lambertsk = reflectivity 0<k<1E = illuminance in foot-candles (lumens/ foot^2)
Obviously, if you divide a luminance expressed in foot-Lamberts by pi you then have the luminanceexpressed in candles /foot^2. (Bfl/pi=B)
Other luminance units are:
stilb = 1 candle/square centimeter sbapostilb = stilb/(pi X 10^4)=10^-4 L asb
nit = 1 candle/ square meter ntLambert = (1/pi) candle/square cm L
Below is a table of photometric units with short definitions.
Symbol Term Unit Unit Definition
Q light quantity lumen-hour radiant energylumen-second as corrected for eye's
spectral response
F luminous flux lumen radiant energy fluxas corrected for eye's
spectral response
I luminous intensity candle one lumen per steradicandela one lumen per steradicandlepower one lumen per steradi
E illumination foot-candle lumen/foot^2lux lumen/meter^2phot lumen/centimeter^2
B luminance candle/foot^2 see unit def's. abovefoot-Lambert = (1/pi) candles/foot^2Lambert = (1/pi) candles/centim
Quantity of light, Q, is akin to a quantity of photons except that here the number of photons is pro-rataccording to how bright they appear to the eye.
Luminous flux, F, is akin to the time rate of flow of photons except that the photons are pro-rated accto how bright they appear to the eye.
Luminous intensity, I, is the solid-angular density of luminous flux. Applies primarily to point sourceIllumination, E, is the areal density of incident luminous flux. Luminance, B, is the areal intensity of extended source.
Photometry with a Photographic Light Meter
The first caveat to keep in mind is that the average unfiltered light meter doesn't have the same spectrsensitivity curve that the human eye does. Each type of sensor used has its own curve. Silicon blue cearen't too bad. The overall sensitivity of a cell is usually measured with a 2856K or 2870K incandesclamp. Less commonly it is measured with 6000K sunlight.
The basis of using a light meter is the fact that a light meter uses the Additive Photographic ExposureSystem, the system which uses Exposure Values:
Ev = Av + Tv = Sv + Bv
where: Ev = Exposure ValueAv = Aperture Value = lg2 N^2 where N = f-numberTv = Time Value = lg2 (1/t) where t = time in sec.sSv = Speed Value = lg2 (0.3 S) where S = ASA speedBv = Brightness Value = lg2 Bfl
From the preceeding two equations you can see that if you set the meter dial to an ASA speed of approximately 3.1 (same as Sv = 0), when you read a scene luminance level the Ev reading will be Bwhich you can calculate Bfl. If you don't have an ASA setting of 3.1 on your dial, just use ASA 100 subtract 5 from the Ev reading to get Bv. (Sv@ASA100=5)
If you know the object luminance (photometric brightness), the f-number of the lens, and the imagemagnification, you can calculate the image illumination. The image magnification is the quotient of alinear dimension in the image divided by the corresponding linear dimension on the object. It is, in th
photographic case, a number less than one. The f-number is the f-number for the lens when focussed infinity - this is what's written on the lens. The formula that relates these quantities is given below:
Eimage = (t pi B)/[4 N^2 (1+m)^2]or: Eimage = (t Bfl)/[4 N^2 (1+m)^2]where: Eimage is in foot-candles (divide by .0929 to get lux)
t is the transmittance of the lens (usually .9 to .95 but lofor more surfaces in the lens or lack of anti-reflection
coatings)B is the object luminance in candles/square footBfl is the object luminance in foot-LambertsN is the f-number of the lensm is the image magnification
References:
G.E. Miniature Lamp CatalogGilway Technical Lamp Catalog"Lenses in Photography" Rudolph Kingslake Rev.Ed.c1963 A.S.Barnes"Applied Optics & Optical Engr." Ed. by Kingslake c1965 Academic Press"The Lighting Primer" Bernard Boylan c1987 Iowa State Univ."University Physics" Sears & Zemansky c1955 Addison-Wesley
The Canon EOS system of digital single-lens reflex (SLR) bodies and lenses is the standard choice amprofessional photographers worldwide. This page makes it easy to shop for Canon digital bodies and
lenses. Every component manufactured by Canon is covered, plus a few exceptionally good third-parcomponents. If you are new to photography, you might want to start with our article "Building a DigiSLR System".
This article goes through every section of the Canon EOS system and concludes with some starter syrecommendations.
Small sensor bodies are good for telephoto work, such as wildlife photography. A 100mm telephoto that would be ideal for portraits on a film or full-frame sensor body gives a 150mm equivalent perspeon a small sensor ("APS-C") body. The full-frame sensor bodies are good for wide angle photographlight photography, and ultimate image quality.
small sensor
• Canon Digital Rebel XTi (Black) (review), introduced October 2006, the right camera for moconsumers who want a responsive accurate machine (replaces the similarly named, but obsolete, CanDigital Rebel XT, $444 (review))• Canon Digital Rebel XSi , $485 (review), the new replacement for the Rebel XTi• Canon EOS 40D (review), larger and heavier than the Rebel with comparable image quality acapabilities, but more convenient controls; great camera for wildlife and sports photography• Canon EOS 50D , $930 (review), an upgrade to the EOS 40D, which includes Live View• Canon EOS 1D Mark III , $3570 (review), the ideal camera for professional sports photograph
full-frame sensor
• Canon EOS 5D (review), the best camera for most advanced amateurs and professionals• Canon EOS 5D Mark II (review), with 21MP and HD video capabilities—do more with a camthan you have ever been able to before• Canon EOS 1Ds Mark III , $6115 (review), same size and weight as a brick; weather-sealed arain and dust
For nostalgia buffs, Canon still makes some film bodies that work with all of the lenses below, excepmarked "small sensor only". And older Canon film bodies that
•
Canon EOS-1V Professional SLR Body , $1650 (review), fully weather-sealed professional bowith 100 percent viewfinder coverage• Canon EOS-3 35mm SLR Camera (Body Only) , $945 (review), just about as useful as the 1Vwithout the 100-percent viewfinder • Canon EOS Elan 7ne 35mm Film Body , $343, bulkier than the Rebel with a rear control whelike the big Canon bodies• Canon Rebel T2 , $205, pair with Canon EF 50mm f/1.8 II, $93 (review), for a cheap, light, hiquality, general-purpose camera• Canon EOS Rebel K2 , $130, pair with Canon EF 50mm f/1.8 II, $93 (review)
An EOS-3 is good enough for almost any photographic purpose, it is incredibly rugged, and you shou
able to buy one cheap in the photo.net classifieds.
Nomenclature
F-number: lower is better.
IS is "image stabilization", a technology lifted from camcorders in which the camera electronicallycompensates for unsteady hands. IS is especially important at long focal lengths, e.g., 200mm and ab
because the lens magnifies camera shake at the same time it is magnifying the subject. An IS lens wiyou to use slower shutter speeds without introducing camera shake. The alternative to an IS lens woumounting the camera on a tripod or using a high ISO setting, which reduces image quality but allowsof higher shutter speeds.
USM is "ultrasonic motor". All Canon EOS-system lenses have built-in focus motors. There is no mothe body as is the case with Nikon, for example. The cheaper Canon lenses have a motor that must beclutched out with a switch if the photographer wishes to focus manually. When using a USM lens, thphotographer can push the shutter release (or a button on the rear of the camera, if a custom functionand let the autofocus system do its best, then touch up the focus manually by twisting the lens ring.
The L lenses are Canon's expensive lenses designed for professional photographers. An L lens will alhave good optical performance, even if it is a wide-range zoom that is challenging to design. An L lenalways be mechanically tough and well-sealed against water and dust. An L lens might be very heavyexpensive. Note that there are some non-L prime (fixed focal length or non-zoom) lenses, such as the50/1.4, that offer extremely high optical quality. The non-L Canon zoom lenses are optimized for ligh
weight and low cost and won't be especially high in optical quality.
EF-S lenses are designed for Canon's small-sensor digital cameras, such as the Digital Rebel. The "E"EF-S" is the standard Canon EOS "Electro-Focus" mount, introduced in 1987. The "-S" stands for "back focus" and means that the lens design protrudes more deeply into the camera body. This protruswould damage a full-frame camera's mirror, so a mechanical interlock prevents these lenses from beimounted on a standard EOS camera. An EF-S lens will work with any of the small-sensor bodies intrsince 2003, including the original Digital Rebel (300D) and the 20D.
Normal Lenses
A normal or standard lens is light in weight and approximates the perspective of the human eye. Normlenses have large maximum apertures, indicated by small f-numbers such as f/1.4 or f/1.8, and therebgather much more light than zoom lenses. It may be possible to take a photo with a normal lens in lig1/8th or 1/16th as bright as would be required for the same photo with a consumer-priced zoom lens.Another advantage of the large maximum aperture is that the viewfinder will be correspondingly brigand therefore easier to use in dim light. (SLRs keep the lens wide open for viewing and stop down towhatever aperture you have set just before taking the picture; this is why the viewfinder always lookssame even if you switch from f/1.4 to f/8 to f/16.)
• Sigma 30/1.4 , $439, ultrasonic motor, equivalent to a 45mm perspective on a film or full-framcamera; Canon does not bother to make a competitive lens
full-frame sensor (EOS 5D)
• Canon EF 50mm f/1.4 USM , $349 (review), includes an ultrasonic motor that allows simultanuse of manual and autofocus, high quality (metal) mechanical construction• Canon EF 50mm f/1.8 II , $93 (review), cheap plastic case, high image quality, no ultrasonic mand therefore autofocus is slower, noisier, and harder to override with a manual twist
In terms of flare, contrast, and sharpness, these are the highest quality lenses that you will ever attachyour camera. If you can do the job with a 50/1.4, as many of the 20th Century's greatest photographeyou can save yourself a lot of weight and cost. There are good zoom lenses, mostly in the Canon L sebut they are very expensive and heavy.
Wide-to-Telephoto Zoom Lenses
A wide-to-tele zoom is what you get as a standard "kit" lens with a cheaper digital SLR body. The ragoes from moderately wide through normal to moderately telephoto. They are good when you are tooto change lenses, e.g., at a wedding reception. The 24mm perspective (full-frame) will capture a tableguests; the 70mm or 105mm long end is good for a flattering portrait. The main weakness of these lethat the cheaper ones have a very small maximum aperture, e.g., f/4 or f/5.6, and can only be used in
light, on a tripod, or with a blast of on-camera flash that gives everyone a moon face.
digital-only
• Canon EF-S 17-55 f/2.8 IS USM , $1060 (review), if you have a small sensor and must have amidrange zoom, this is the one to get; f/2.8 and L-class image quality would make it a good lens; imastabilization makes it a great lens
• Canon EF-S 17-85mm f/4-5.6 IS USM , $450, image stabilization will enable you to handholdshutter speeds indoors and therefore despite the slow maximum aperture, you might not have to use fthe time--you will still suffer with a dim viewfinder • Canon EF-S 18-55mm f/3.5-5.6 USM (review), the "kit" lens that Canon tosses in with most Digital Rebels sold, works well enough outdoors on bright sunny days
full-frame
• Canon EF 24-70mm f/2.8L USM , $1329 (review), heavy, but very high quality and the ultimawedding reception tool• Canon EF 24-85mm f/3.5-4.5 USM (review)• Canon EF 24-105mm f/4 L IS USM , $1059 (review), much lighter than the 24-70, but still suoptical quality, the loss of one f-stop compensated for somewhat by the provision of image stabilizati• Canon EF 28-80mm f/3.5-5.6 II , $150, cheap "kit" lens designed for the film Rebel• Canon EF 28-90mm f/4-5.6 II USM , $98 (review), cheap "kit" lens with a faster quieter autof• Canon EF 28-105mm f/3.5-4.5 II USM , $249 (review), reasonably cheap, reasonably good fo
outdoor use• Canon EF 28-105mm f/4-5.6 USM , $149 (review), spectacularly cheap, spectacularly crumm• Canon EF 28-135mm f/3.5-5.6 IS USM , $410 (review), average image quality, image stabilizuseful if you must take pictures from an unstable platform, such as a boat• Canon EF 28-200mm f/3.5-5.6 USM , $375, convenient range, acceptable image quality if usetripod and stopped down to f/8• Canon EF 28-300mm f/3.5-5.6L IS USM , $2420 (review), incredibly heavy, exceptional rangreasonably good quality, image stabilizer enables handheld use at longer focal lengths without the ustripod or flash
Here are a few photos from my brother's wedding, taken with a discontinued Canon 28-70/2.8L (supe
Good for general-purpose dramatic wide angle photography. More distortion than wide-angle prime which makes them less suitable for photographing architecture (though many kinds of distortion can fixed by a PhotoShop wizard).
small sensor (Rebel and 30D)
• Canon EF-S 10-22mm f/3.5-4.5 USM , $770 (review), a touch slow, but dramatically wide
full-frame sensor
• Canon EF 16-35mm f/2.8L USM , $1520 (review), zoom from very dramatic (16mm) to borin(35mm) wide angle• Canon EF 17-40mm f/4L USM , $750 (review)• Canon EF 20-35mm f/3.5-4.5 USM
Telephoto Zoom Lenses
These are good complements to a normal lens when traveling. The long end may not be useful indooto a small maximum aperture.
small-sensor only
• Canon EF 55-200mm f/4.5-5.6 II USM , cheap, slow, and crummy
• Canon EF-S 55-250mm f/4.0-5.6 IS , $255 (review), Canon's latest zoom IS lens
full-frame
• Canon EF 70-200mm f/2.8L IS USM , $1799 (review), the image-stabilized version of the cla
200 zoom lens, good for portraits and stretchable with a Canon EF 1.4X II Extender , $309 (review)• Canon EF 70-200mm f/2.8L USM , $1300 (review), just as good (and heavy) optically, but wiimage stabilization• Canon EF 70-200mm f/4L USM , $639 (review), a good lens for travel, especially given the dcamera's ability to be reset for a higher ISO speed; too bad that it doesn't come with image stabilizati• Canon EF 70-200mm f/4 L IS USM , $1210 (review), all the same details as the previous lensincludes image stabilization• Canon EF 70-300mm f/4-5.6 IS USM , $549 (review), remember that these slow maximum aplenses aren't good for stopping action, even if the image stabilizer cuts down on camera shake; sportsphotography would require a maximum aperture of f/4 or f/2.8 rather than the f/5.6 this lens provides• Canon EF 70-300mm f/4.5-5.6 DO IS USM , $1250 (review)•
Canon EF 75-300mm f/4-5.6 III , $160• Canon EF 75-300mm f/4-5.6 III USM , $200• Canon EF 80-200mm f/4.5-5.6 II , $146• Canon EF 100-300mm f/4.5-5.6 USM • Canon EF 100-400mm f/4.5-5.6L IS USM , $1610
Interesting third-party lenses:
• Sigma 300-800/5.6 HSM , $7995, ultrasonic motor, good for covering an airshow where you nrange and don't have time to switch focal lengths
Wide-angle Prime Lenses
These let you get close to your subject while still showing a lot of background information. Wide anglenses are good for "environmental portraits" in which the subject occupies most of the frame, but neobjects are in sharp focus. Photojournalism has gone gradually wider and wider over the years. A typphoto in a newspaper these days might be taken at 20-24mm on a full-frame camera.
A prime wide angle lens will have much lower distortion of vertical and horizontal lines than a zoomand is therefore preferred for architectural photography. All of these lenses are designed for film andframe sensor cameras.
• Canon EF 14mm f/2.8L USM , $2199 (review), a great lens, but difficult to use effectively• Canon EF 15mm f/2.8 Fisheye Lens , $649 (review), the fisheye effect was cool when Playboymagazine was "groovy"• Canon EF 20mm f/2.8 USM , $470, the modern photojournalist's standard lens• Canon EF 24mm f/1.4L USM (review)•
Canon EF 24mm f/2.8 , $340, an old design without USM• Canon EF 28mm f/1.8 USM , $459• Canon EF 28mm f/2.8 , $259, an old design without USM• Canon EF 35mm f/1.4L USM , $1400, designed for professional photojournalists who need asomewhat wide perspective and who need to work in dim light• Canon EF 35mm f/2 , $299, an old design without USM
Telephoto Prime Lenses
A prime or fixed focal length telephoto lens offers maximum image quality, light gathering capability(aperture), and magnification. The good ones are big, heavy, and designed for use on a monopod or tSports and wildlife photography require these lenses.
• Canon EF 85mm f/1.2L II USM , $1970 (review)• Canon EF 85mm f/1.8 USM , $380 (review), a great gift for a family with a new baby and a smsensor digital camera• Canon EF 100mm f/2 USM , $435 (review)• Canon EF 100mm f/2.8 Macro USM , $529 (review), one f-stop slower, but usable for portraitalso has macro capability• Canon EF 135mm f/2L USM , $999, superb optical quality, ultrasonic motor • Canon EF 135mm f/2.8 Soft Focus , $499, clunky focusing due to lack of ultrasonic motor, unsoft focus feature, adjustable from completely sharp to flatteringly soft
the bigger iron starts here
• Canon EF 200mm f/2.8L II USM , $769, good for fashion photography• Canon EF 200mm f/2L IS USM , $5300• Canon EF 300mm f/2.8L IS USM , $4340 (review), the standard sports photographer's startingheavy, so plan on using a monopod• Canon EF 300mm f/4L IS USM , $1269 (review), much lighter, but not as amenable to autofooperation with a teleconverter as the 300/2.8• Canon EF 400mm f/2.8L IS USM , $7190• Canon EF 400mm f/4 DO IS USM , $5820
• Canon EF 400mm f/5.6L USM , $1209• Canon EF 500mm f/4L IS USM , $6140• Canon EF 600mm f/4L IS USM , $8050 (review), the starting point for serious bird photograp• Canon EF 800mm f/5.6L IS USM , $10900• There is a 1200/5.6L lens that Canon will make to special order for about $75,000
for use with any of the above
• Canon EF 1.4X II Extender , $309 (review), turns a 300/2.8, for example, into a 420/4 (lose onstop)• Canon EF 2X II Extender , $309 (review), turns a 300/2.8, for example, into a 600/5.6 (lose twstops)
The better Canon telephoto lenses are designed to work optically with the tele-extenders. Image qualbe acceptable, even at maximum aperture. As noted above, however, there is no free lunch. A tele-exprovides additional magnification, but the overall amount of light gathered by the lens remains the sa
Thus, you lose one f-stop of light with the 1.4X converter and two f-stops with the 2X converter. Theviewfinder will be dimmer and the camera will have a tougher time autofocusing. With the 2X conveand a slower lens, therefore, you will lose the ability to autofocus with many bodies.
These are heavy lenses. If you have a tripod quick-release system, get plates for each lens and rememmount the lens, not the camera body, to the tripod.
Macro Lenses
Macro lenses let you fill your photograph with a subject that is physically small. The longer the focal
of the macro lens, the farther away you can be from your subject, which is important with live insectexample. A macro lens that goes down to "1:1" can be used to take a frame-filling photo of somethin24x36mm (1x1.5 inches) in size, the same dimensions as a frame of 35mm film or the sensor on a fuldigital body. All Canon macro lenses, except for the MP-E 65mm, can be used for ordinary photograprojects as well, i.e., they will focus out to infinity if desired. In the old days, a lot of photographers wget a 50mm normal lens and then a 100mm macro lens that would double for use with portraits and mprojects.
• Canon EF-S 60mm f/2.8 Macro USM , $422 (review), goes down to 1:1, but remember that thof a small-sensor camera is actually smaller than the 24x36mm film standard, so you can fill the frama subject as small as 15x22mm (the size of a penny)
full-frame
• Canon EF 50mm f/2.5 Macro , $265, an old design that lacks an ultrasonic motor, goes to 1:2;need Canon Life Size Converter EF, $275 to get to 1:1• Canon EF 100mm f/2.8 Macro USM , $529 (review), goes to 1:1, probably the best macro lenthe full-frame crowd• Canon EF 180mm f3.5L Macro USM , $1370 (review), goes to 1:1, good for photographing inwhere you want more separation between the camera and the subject
specialty
• Canon MP-E 65mm f/2.8 1-5X Macro , $950 (review), a unique lens that lets you take picturethings much smaller than the 24x36mm frame; good for photographing details in jewelry, for examplnot focus to infinity like the other macro lenses (see example image at right)
If you are using a non-macro lens and need to focus closer for some reason, you can place either Can12 II Extension Tube, $85 or Canon EF 25 II Extension Tube, $140 between the body and the lens.Extension tubes move the lens farther away from the plane of the sensor. You could, for example, takpictures of just part of a person's face with a telephoto lens. If, however, you then wanted a sharp pica subject at infinity, you'd have to unmount the lens, remove the extension tube, and remount the lens
Tilt-Shift Lenses
The shift part of the tilt-shift lens lets you take a picture of a building, from ground level, without theconverging and making it look as though the building is falling over. To some extent, this is obsoletebecause these kinds of linear distortions can be fixed post-exposure in a digital editing tool such as APhotoShop. The tilt part of a Canon tilt-shift lens lets you control the plane of sharp focus, e.g., if youeverything on a table top to be sharp. This is an effect that must be done at exposure time. A Canon t
lens lets you do many of the perspective and focus adjustments available to a photographer with acumbersome 4x5 view camera (cloth over head, bellows in between film and lens)... at a price that isabout double what a used view camera sells for.
• Canon TS-E 24mm f/3.5L , $1200 (review), good for interiors•
The easiest way to ruin a photograph is to use on-camera flash, which blasts the subject with an unflalight. The resulting lack of shadows means that it is tough for a viewer to make out the features of thesubject. On-camera flash is useful outdoors for filling in harsh shadows. Otherwise, the professional flash mostly bouncing up towards the ceiling or held as far away from the camera as possible. This isthe professional camera bodies don't incorporate the pop-top flashes the way that consumer bodies do
• Canon Speedlite 220EX Flash , $125 (review), cannot be tilted up for bouncing, good for fill-i• Canon Speedlite 430EX II Flash , $280 (review), tilts up, swivels sideways, powerful enough most projects, especially with
a Sto-Fen bounce diffuser
• Canon Speedlite 580EX II Flash , $445 (review), monster power, tilt up at 45-degree angle anbounce diffuser • No product information for canon_580ex_II
• Canon STE2 Speedlite Transmitter , $200, wireless control of EOS flash units that are held or mounted away from the camera (this is the way that most professionals use flash)• Canon Off Camera Shoe Cord , $60 (review), the same idea, but corded and you hold the flashyour left hand while holding the camera body in your right (or use a flash bracket like a weddingphotographer)
• Canon MR-14EX Macro Ring Lite , $495 (review), shadowless uniform illumination; this is wdentists use• Canon MT-24EX Macro Twin Lite Flash , $729 (review), a little more potential for artistic lig
Note that a standard flash, with an off-camera cord and a bit of diffusion material, may be substitutedmacro flash.
For a camera body and one lens, the average professional photographer would not use a case at all. Ta camera system, you should probably find a nearby professional camera shop and experiment to see
your gear fits. I usually end up preferring Tamrac and Lowe cases. Here are a few ideas:
• Tamrac Velocity 7 , for a Digital Rebel and small prime or small (cheap) zoom lenses• LowePro Off Trail 1 , belt back for smaller bodies and lenses• Tamrac 5606 , one 30D or EOS 5D body, two or three professional-sized lenses, one flash
Recommended Starter Systems
Averag family:
• Canon Digital Rebel XTi (Black) (review)• Sigma 30/1.4 , $439, for high quality indoor photos without flash and general photography (zoalternative: Canon EF-S 17-55 f/2.8 IS USM, $1060 (review))• Canon EF-S 10-22mm f/3.5-4.5 USM , $770 (review), for travel• Canon EF 200mm f/2.8L II USM , $769 for sports (equivalent to 300mm on a full-frame camepossibly a telephoto zoom (Canon doesn't make any good telephoto zoom lenses designed specificallthe small-sensor cameras, the Canon EF 70-200mm f/4L USM, $639 (review) is probably the best m
Serious photographer:
• Canon EOS 5D (review)• Canon EF 50mm f/1.4 USM , $349 (review)• Canon EF 16-35mm f/2.8L USM , $1520 (review)• Canon EF 70-200mm f/2.8L IS USM , $1799 (review)
More
• Lens chapter from Making Photographs • Lens Chart from Canon USA
The Nikon system of digital single-lens reflex (SLR) bodies and lenses is a popular choice among sephotographers worldwide. This page makes it easy to shop for Nikon digital bodies and Nikkor lenseEvery component manufactured by Nikon is covered, plus a few exceptionally good third-partycomponents. If you are new to photography, you might want to start with my article "Building a DigiSLR System".
This article goes through every section of the Nikon system and concludes with some starter systemrecommendations.
Nikon Camera Bodies
Most Nikon digital SLR bodies incorporate a "small sensor" or "APS-C" sized sensor. This is smallethe standard 35mm film frame and effectively multiplies the magnification of any lens attached to theA small sensor is good for telephoto work, such as wildlife photography, where a 300mm lens that isshort for bird photography on a film camera becomes a 450mm (effective) lens. In November 2007, Nadded the D3, their first full-frame sensor DSLR professional camera to their arsenal of DSLR bodiefull-frame sensor bodies are good for wide angle photography, low light photography, and optimum quality.
• Nikon D40, 18-55mm kit (review) (discontinued), 6 MP and good enough for most familyphotography; best user interface of any digital SLR, with example photos displayed on the rear LCD show appropriate situations for different settings. Note that the D40 requires SD memory cards rathethe standard CF cards used by other Nikon bodies
• Nikon D40x , $590 (review), same idea, but 10 MP; if you care about image quality, pair with30mm f/1.4 EX DC for Nikon, $439• Nikon D60 , $561 (review), 10 MP, Nikon's latest addition to the line of small-body DSLRs, aupgrade to the D40/D40x• Nikon D80 (review), 10 MP, Nikon's answer to the Canon Digital Rebel XTi; the kit zooms a
reasonably good, but too slow for indoor usage• Nikon D90 , $900 (review), 12 MP, Nikon's latest prosumer model, includes GPS and a moviecapable of capturing 1280x720 pixel images at 24 fps HD with sound.• Nikon D200 (review) (discontinued), 10 MP, great for advanced amateurs• Nikon D300 (review), 12 MP, released at the same time as the D3, a fast camera with 51 AF p• Nikon D2HS , $5987 (review), only 4 Megapixels but tremendously fast; intended for sportsphotojournalists• Nikon D2Xs (review), 12 MP, before the full-frame sensor cameras came along, this was Niktop-of-the-line camera• Nikon D700 , $2697 (review), 12 MP, D3 image quality at about half the price• Nikon D3 (review), 12 MP, Nikon's first full frame sensor DSLR •
Nikon D3X , $7999 (review), 24.5 MP, D3 image quality with about double the resolution• Nikon D3s , $5200 (review), 12MP, D3 image quality with ISO up to 12,800 (102,400 with boand HD video capture
For nostalgia buffs and collectors, Nikon still makes film bodies:
in-production
• Nikon F6 , $2399 (review), autofocus, probably the best 35mm film SLR that will ever be mad• Nikon FM10 with 35-70 lens , $320, manual focus, designed for students in intro photographyclasses
discontinued
• Nikon F5 , $1100• Nikon F100 , $550 (review), much lighter and smaller than the F-series and almost as durablewas the standard "second body" that professionals carried in the film days• Nikon N80 , $217 (review), mostly plastic body, reasonably good autofocus and autoexposuresystems; rememeber that it is the lens that determines image quality (might actually be cheaper as a ka crummy lens: Nikon N80 with 28-80 lens, $300 (review))• Three incredibly cheap, all plastic, not very good bodies: Nikon N55, $150;
Nikon N65, $488 (review); Nikon N75, $129
• Nikon FM3A , $800 (review), hard to find; Nikon came out with this all-metal manual focus b2001. It is a beautifully balanced camera and, with a 50/1.4 lens, will take much better pictures than wpercent of digital camera owners capture with their cheap kit zoom lenses.
VR is "vibration reduction", a technology lifted from camcorder image stabilizers. The lens electronicompensates for unsteady hands. VR is especially important at long focal lengths, e.g., 200mm and abecause the lens magnifies camera shake at the same time it is magnifying the subject. A VR lens wi
you to use slower shutter speeds without introducing camera shake. The alternative to a VR lens woumounting the camera on a tripod or using a high ISO setting, which reduces image quality but allowsof higher shutter speeds.
"ED" is "extra-low dispersion" glass, a more expensive and higher quality glass that reduces chromataberration, in which light of different colors takes different paths through the lens, which would resuldot of white light being fuzzed up by the time it reaches the film or sensor.
"IF" is internal focus, meaning that the lens does not change physical length as you focus on subjectsare closer or farther away.
"DX" are Nikon's lenses that only work on its small-sensor digital SLR bodies, i.e., they don't cast a lenough image circle to be used on a film camera.
"FX" refers to the full frame sensor
"G" lenses are Nikon's newest lenses. They don't have an aperture ring, which is a shame because it mthat you are forced to adjust the aperture with a command wheel on the camera. The G lenses don't wolder bodies.
AF-S is "silentwave motor". Old-style Nikon autofocus lenses did not have motors in the lens, but rea screwdriver blade in the camera body to turn the focus ring. An AF-S lens has a built-in ultrasonic
a technology copied from the Canon EOS system. When using an AF-S lens, the photographer can pushutter release (or a button on the rear of the camera, if a custom function is set) and let the autofocussystem do its best, then touch up the focus manually by twisting the lens ring. The AF-S lenses also ffaster and more quietly.
A normal or standard lens is light in weight and approximates the perspective of the human eye. Normlenses have large maximum apertures, indicated by small f-numbers such as f/1.4 or f/1.8, and therebgather much more light than zoom lenses. It may be possible to take a photo with a normal lens in lig1/8th or 1/16th as bright as would be required for the same photo with a consumer-priced zoom lens.Another advantage of the large maximum aperture is that the viewfinder will be correspondingly brig
and therefore easier to use in dim light. (SLRs keep the lens wide open for viewing and stop down towhatever aperture you have set just before taking the picture; this is why the viewfinder always lookssame even if you switch from f/1.4 to f/8 to f/16.)
digital bodies
• Sigma 30mm f/1.4 EX DC for Nikon , $439, ultrasonic motor, equivalent to a 45mm perspectfilm camera; Nikon does not bother to make a competitive lens• Nikon 35mm f/2.0 AF , $360 (review); designed for a film camera and the viewfinder will be half as bright as the Sigma, but possibly higher optical quality, especially since you're only using the portion of the lens.
film AF
• Nikon 50mm f/1.8D AF Nikkor , $124, a great lightweight bargain and one of the highest optiquality lenses in the Nikon line; you could use this as a portrait lens on a digital SLR • Nikon 50mm f/1.4D AF Nikkor , $320 (review), less than one f-stop faster than the 1.8; similaoptical quality
film manual focus
• Nikon 45mm f/2.8 Nikkor AI-S Manual Focus , $400, very compact and designed cosmeticall
with the FM3a nostalgia body• Nikon 50mm f/1.2 Nikkor AI-S Manual Focus , $670, a half-stop faster than the 50/1.4, but yoautofocus and the image quality at f/1.2 is not very good
In terms of flare, contrast, and sharpness, these are the highest quality lenses that you will ever attachyour camera. If you can do the job with a normal lens, as many of the 20th Century's greatest photogrdid, you can save yourself a lot of weight and cost. There are good zoom lenses, but they are very expand heavy.
A wide-to-tele zoom is what you get as a standard "kit" lens with a cheaper digital SLR body. The ragoes from moderately wide through normal to moderately telephoto. They are good when you are tooto change lenses, e.g., at a wedding reception. The 24mm perspective (full-frame) will capture a tableguests; the 70mm or 105mm long end is good for a flattering portrait. The main weakness of these lethat the cheaper ones have a very small maximum aperture, e.g., f/4 or f/5.6, and can only be used in
light, on a tripod, or with a blast of on-camera flash that gives everyone a moon face.
made for the small-sensor digital cameras
• Nikon 17-55mm f/2.8G ED-IF AF-S DX , $1340• Nikon 18-55mm f/3.5-5.6G ED AF-S DX , $230• Nikon 18-70mm f/3.5-4.5G ED IF AF-S DX • Nikon 18-135mm f/3.5-5.6G ED-IF AF-S DX • Nikon 18-200mm f/3.5-5.6G ED-IF AF-S VR DX , this kind of super wide range zoom is typinot very good, but Nikon lards on the dollars and the weight (more than one pound) and the results aracceptable; the vibration reduction compensates to some extent for the slow maximum aperture of f/5•
Nikon 24-70mm f/2.8G ED AF-S , $1740• Nikon 24-85mm f/2.8-4.0D IF AF , $540
leftovers from the film days
• Nikon 24-85mm f/2.8-4.0D IF AF , $540• Nikon 24-85mm f/3.5-4.5G ED-IF AF , $410• Nikon 24-120mm f/3.5-5.6G ED-IF AF VR , $560• Nikon 28-70mm f/2.8D ED-IF AF-S , $1700, big and heavy, but fast and constant aperture; thstandard tool for wedding photographers• Nikon 28-80mm f/3.3-5.6G AF (Black) , $250, kit lens for Nikon's cheapest film bodies•
Nikon 28-105mm f/3.5-4.5D , $279, reasonably good, reasonably light, reasonably cheap• Nikon 28-200mm f/3.5-5.6G ED IF , $425, no vibration reduction and therefore unlikely to beat the 200mm f/5.6 end unless you are willing to carry a tripod• Nikon 35-70mm f/2.8D AF , $900, superseded to a large extent by the 28-70/2.8, but still a vequality lens; no silentwave motor
Wide-angle Zoom Lenses
Good for general-purpose dramatic wide angle photography. More distortion than wide-angle prime which makes them less suitable for photographing architecture (though many kinds of distortion can fixed by a PhotoShop wizard).
made for the small-sensor digital cameras
• Nikon 12-24mm f/4G ED IF Autofocus DX , $999 (review)• Nikon 14-24mm f/2.8G ED AF-S , $1825
• Nikon 17-35mm f/2.8D ED-IF AF-S , $1765, the professional's lens, with its fast and constantmaximum aperture, turns into a moderately wide to normal very high quality zoom lens on a Nikodigital SLR •
Nikon 18-35mm f/3.5-4.5D ED-IF AF , $540, a reasonably good alternative
Telephoto Zoom Lenses
These are good complements to a normal lens when traveling. The long end may not be useful indooto a small maximum aperture.
made for the small-sensor digital cameras
• Nikon 55-200mm f4-5.6G ED AF-S DX Nikkor Zoom (Black) , $175, cheap, slow, cru• Nikon 70-200mm f/2.8G ED VR II AF-S , $2319, version 2 of the popular 70-200/2.8 with improved VR
leftovers from the film days
• Nikon 70-200mm f/2.8G ED-IF AF-S VR , the standard professional choice, and a good lens fdigital SLR too; very heavy• Nikon 70-300mm f/4-5.6D ED AF , $319• Nikon 70-300mm f/4-5.6G AF Nikkor SLR Camera , $155, half the weight, half the cost, halfoptical quality of the 70-300/5.6D• Nikon 80-200mm f/2.8D ED AF Zoom Nikkor , $1100 (review), no silentwave motor, no vibrreduction, shoulder-crushing weight, high optical quality, superseded by the 70-200 AF-S VR lens• Nikon 80-400mm f/4.5-5.6D ED Autofocus VR Zoom Nikkor , $1650
Wide-angle Prime Lenses
These let you get close to your subject while still showing a lot of background information. Wide anglenses are good for "environmental portraits" in which the subject occupies most of the frame, but ne
objects are in sharp focus. Photojournalism has gone gradually wider and wider over the years. A typphoto in a newspaper these days might be taken at 20-24mm on a full-frame camera, which would be17mm on a small sensor digital camera.
A prime wide angle lens will have much lower distortion of vertical and horizontal lines than a zoomand is therefore preferred for architectural photography. All of these lenses are designed for film andframe sensor cameras.
• Nikon 10.5mm f/2.8G ED AF DX Fisheye , $695, very wide, very curved corners, good for thcramped interior of a submarine; considered a "groovy" effect back in the 1960s
leftovers from the film days
• Nikon 14mm f/2.8D ED AF , $1400• Nikon 16mm f/2.8D AF Fisheye , $930, full-frame fisheye• Nikon 18mm f/2.8D AF , $1500• Nikon 20mm f/2.8D AF , $565 (review), a focal length that became popular in the 1980s for
photojournalism, but not dramatically wide on a Nikon digital SLR • Nikon 24mm f/2.8D AF , $360 (review)• Nikon 28mm f/1.4D AF , $2380• Nikon 28mm f/2.8D AF , $265• Nikon 35mm f/2.0 AF , $360 (review)
A prime or fixed focal length telephoto lens offers maximum image quality, light gathering capability(aperture), and magnification. The good ones are big, heavy, and designed for use on a monopod or tSports and wildlife photography require these lenses. Nikon does not make any telephoto lenses specfor their small-sensor digital cameras, which is a shame because it would be possible to cut the cost aweight dramatically without the requirement of casting a 24x36mm image for an old film camera.
leftovers from the film days
• Nikon 85mm f/1.4D AF Nikkor , $1225• Nikon 85mm f/1.8D AF Nikkor , $450• Nikon 105mm f/2.0D AF DC-Nikkor , $1080, first of Nikon's innovative lens design giving thphotographer the ability to throw foreground or background intentionally out of focus• Nikon 135mm f/2.0D AF DC-Nikkor , $1300, the other Nikon lens that lets you selective blurportions of the image• Nikon 180mm f/2.8D ED-IF AF , $890, an incredibly sharp and light lens, standard choice forfashion photographers with full-frame film bodies in the late 1980s; becomes the equivalent of a 300lens on a Nikon digital body and therefore good for animals in the zoo and dramatic telephoto image• Nikon 200mm f/2.0G ED AF-S VR , $4999 (review)
• Nikon 200-400mm f/4G IF-ED AF-S VR , $6100, a great lens for wildlife• Nikon 300mm f/2.8 ED-IF AF-S , $4490 (review), the standard lens for sports photographers,supplemented by a teleconverter • Nikon 300mm f/4.0D ED-IF AF-S , $1485• Nikon 400mm f/2.8D ED-IF AF-S, the same idea as the 300/2.8, but a bit more magnification
weight, and expense• Nikon 400mm f/2.8G ED AF-S , $8800
• Nikon 500mm f/4D ED-IF AF-S , $7900, about the same size as the 300/2.8, but more magnifand smaller maximum aperture• Nikon 500mm f4D ED-IF II AF-S , $7900• Nikon 600mm f/4 ED-IF II AF-S, bigger than a 300/2.8, more expensive than a Kia subcompsedan• Nikon 600mm f/4D ED-IF II AF-S , available soon (as of August 2007)
manual focus
•
Nikon 85mm f/1.4 Nikkor AI-S Manual Focus , $1350, a very poor value compared to the newautofocus 85/1.4• Nikon 135mm f/2.8 Nikkor AI-S Manual Focus , $570
• Nikon 500mm f/8.0 Reflex-Nikkor Manual Focus , $1000; mirror lenses are slow and out-of-fhighlights have an unnatural donut shape; just because it works on the Hubble Space Telescope doesnmean that it will work for you...
Teleconverters
• Nikon TC-14E II 1.4x AF-S, AF-I Auto Focus Teleconverter , $400• Nikon TC-17E II (1.7x) Teleconverter AF-S , $460•
The better Nikon telephoto lenses are designed to work optically with the teleconverters. Image qualibe acceptable, even at maximum aperture. As noted above, however, there is no free lunch. A teleconprovides additional magnification, but the overall amount of light gathered by the lens remains the saThus, you lose one f-stop of light with a 1.4X converter and two f-stops with a 2X converter. Theviewfinder will be dimmer and the camera will have a tougher time autofocusing. With a 2X convert
slower lens, therefore, you will lose the ability to autofocus with many bodies.
These are heavy lenses. If you have a tripod quick-release system, get plates for each lens and rememmount the lens, not the camera body, to the tripod.
Macro lenses let you fill your photograph with a subject that is physically small. The longer the focalof the macro lens, the farther away you can be from your subject, which is important with live insectexample. A macro lens that goes down to "1:1" can be used to take a frame-filling photo of somethin24x36mm (1x1.5 inches) in size, the same dimensions as a frame of 35mm film or the sensor on a fuldigital body. All Nikon macro lenses can be used for ordinary photographic projects as well, i.e., they
focus out to infinity if desired. Note that a "macro zoom" will focus reasonably close, but is not a subfor a "macro lens".
• Nikon 60mm f/2.8D AF Micro-Nikkor , $470 (review)• Nikon 105mm f/2.8G ED-IF AF-S VR Micro Nikkor , $890, a new design with everything goa lens can have.. image stabilizer, internal focus, ultrasonic autofocus motor, 9-bladed diaphragm forattractive out-of-focus highlights ("bokeh"); maximum magnification 1:1• Nikon 200mm f/4.0D ED-IF AF Micro-Nikkor , $1650, good for photographing insects and insituations where you need to get farther back from your subject
Flashes
The easiest way to ruin a photograph is to use on-camera flash, which blasts the subject with an unflalight. The resulting lack of shadows means that it is tough for a viewer to make out the features of thesubject. On-camera flash is useful outdoors for filling in harsh shadows. Otherwise, the professional flash mostly bouncing up towards the ceiling or held as far away from the camera as possible. This isthe professional camera bodies don't incorporate the pop-top flashes the way that consumer bodies do
• Nikon SB-600 Speedlight , $220 (review), bounces up, bounces sideways, zooms in and out, tflash for most consumers• Nikon SB-800 AF Speedlight (review), same basic idea as the SB-600, but more power; builtultra wide angle adaptor • Nikon SB-30 AF Speedlight , $88, a simpler flash, good for on-camera fill light or in a multipsetup• Nikon R1 Wireless Close-Up Speedlight System , $459, great macro flash system to use with
that have a built-in flash, such as the D200
bodies that have a built-in flash, such as the D200
• Nikon R1C1 Wireless Close-Up Speedlight System , $730, the same idea, but for bodies such D2x that do not have a built-in flash
Nikon makes a great line of products, both wired and wireless, for coordinating and controlling multiflashes. Covering all of these accessories is beyond the scope of this article, but if you are going to uas a primary light you should consider added additional speedlights and mounting them off-camera.
Perspective Correction Lenses
A perspective correction (PC) lens lets you take a picture of a building, from ground level, without thconverging and making it look as though the building is falling over. It works because you are able tothe front portion of the lens up, the lens being designed to cast a larger image than the 35mm film frasome extent, this is obsolete because these kinds of linear distortions can be fixed post-exposure in a editing tool such as Adobe PhotoShop. Some of Nikon's older PC lenses were designed for their filmand are manual focus. If you are deeply interested in in-camera perspective adjustments, note that Camakes a more flexible line of "tilt-shift" lenses that come closer to what is possible with a 4x5 view c(cloth over head, bellows, sheet film).
• Nikon 28mm f/3.5 PC Manual Focus , $1350• Nikon 85mm f/2.8 PC Micro-Nikkor , offers very close focusing for macro work as well asperspective correction
For a camera body and one lens, the average professional photographer would not use a case at all. Ta camera system, you should probably find a nearby professional camera shop and experiment to see your gear fits. I usually end up preferring Tamrac and Lowe cases. Here are a few ideas:
• Tamrac Velocity 7 , for a D40 or D80 and small prime or small (cheap) zoom lenses• LowePro Off Trail 1 , belt back for smaller bodies and lenses• Tamrac 5606 , one D200 body, two or three professional-sized lenses, one flash
• Nikon D40, 18-55mm kit (review)• Sigma 30mm f/1.4 EX DC for Nikon , $439 for indoor photos without flash (zoom alternative17-55mm f/2.8G ED-IF AF-S DX, $1340)• Nikon 12-24mm f/4G ED IF Autofocus DX , $999 (review) for the first family trip• Nikon 180mm f/2.8D ED-IF AF , $890 for the soccer game• Lexar 2GB SD card (SanDisk SD cards are supposedly prone to failure)
Serious photographer:
• Nikon D200 (review)• Sigma 30mm f/1.4 EX DC for Nikon , $439• Nikon 12-24mm f/4G ED IF Autofocus DX , $999 (review)• Nikon 70-200mm f/2.8G ED-IF AF-S VR • SanDisk 8 GB CF card
More
• Lens chapter from Making Photographs • Nikon discussion forum
