Date post: | 19-Jan-2016 |
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Lenses
Contain both convex and concave lenses
Lenses
Many concave and convex lenses, called elements are grouped together to produce a specific magnification and correct color aberrations
Lenses
Each element adds the chance for reflection in the lens
Called lens flare
Focal Length
A measurement of the magnifying power of a lens
Focal Length
As magnification increases, field of view decreases
50mm - normal film lens
Prime and Zoom Lenses
Prime Lens -fixed focal length
Zoom - can adjust the focal length (magnification)
Exposure
Too much light, the picture is overexposed
Too little light, the picture is underexposed
Exposure
A camera has two mechanical mechanisms for controlling exposure:
ApertureShutterShutter, Aperture (in the lens)
Exposure - Aperture
An expandable opening like the iris of your eye that controls how much light passes through the lens
Exposure - Aperture
Usually constructed of thin, sliding, interlocking metal plates
Exposure - Aperture
As you close the iris down to a smaller aperture, it stops more light from reaching the image sensor
Exposure - Aperture
The size of the aperture is measured in stops or f-stops
The higher the f-stop rating, the more light the aperture is stopping
Exposure - Aperture
“Lens speed” is determined by how wide its iris or aperture can open.
The wider the aperture, the faster the exposure can be.
Exposure - Fast lenses
A lens that can be opened to f1.8 is much faster than a lens that can only open to f4.
Can shoot in lower light and have a wider range of aperture settings - more creative freedom.
More difficult to build - more expensive
Exposure - Aperture
Aperture and shutter speed are interrelated
Exposure - Shutter
Opens and closes very quickly to control how much light passes through to the image sensor
Exposure - Shutter
Shutter speed is a measure of how long the shutter stays open, measured in seconds and fractions of seconds
Exposure - Reciprocity
Means that many different shutter speed/aperture settings all yield the same exposure
1/30 @ f16
1/60 @ f11
1/125 @ f8
Exposure - Reciprocity
If shutter speed or aperture is shifted in one direction, the other is shifted in the opposite direction the same amount.
Exposure - Reciprocity
If a proper exposure calls for 1/60 sec. and f16, what should the f-stop be if the exposure time was decreased to 1/125?
Exposure - Reciprocity
ISO can also affect shutter speed and/or aperture settings
Exposure - Reciprocity
Every time the ISO value is doubled, it makes the image sensor twice as sensitive
Each value = 1 stop
Exposure - Reciprocity
The higher the ISO value, the more noise there is in the picture, similar to grain in an image made from film with a higher ISO.