Focusing and Accomodation - SFU.ca · Neil Alberding (SFU Physics) Physics 121: Optics, Electricity...

$Page 1: Focusing and Accomodation - SFU.ca · Neil Alberding (SFU Physics) Physics 121: Optics, Electricity & Magnetism Spring 2010 1 / 9. Focusing and Accomodation Most of the refracting$
Focusing and Accomodation

Most of the refracting power of theeye comes from the air-corneaboundary, not from the lens.

Things are blurry underwater becauseyou have a water-cornea boundaryinstead with little difference in n.An eye focuses by changing the focallength of the lens using the ciliarymuscles to change the curvature.This is known as accomodation.Relaxed muscles give a long f ,contracted gives small f .

Neil Alberding (SFU Physics) Physics 121: Optics, Electricity & Magnetism Spring 2010 1 / 9


Most of the refracting power of theeye comes from the air-corneaboundary, not from the lens.Things are blurry underwater becauseyou have a water-cornea boundaryinstead with little difference in n.

An eye focuses by changing the focallength of the lens using the ciliarymuscles to change the curvature.This is known as accomodation.Relaxed muscles give a long f ,contracted gives small f .



Most of the refracting power of theeye comes from the air-corneaboundary, not from the lens.Things are blurry underwater becauseyou have a water-cornea boundaryinstead with little difference in n.An eye focuses by changing the focallength of the lens using the ciliarymuscles to change the curvature.This is known as accomodation.

Relaxed muscles give a long f ,contracted gives small f .



Most of the refracting power of theeye comes from the air-corneaboundary, not from the lens.Things are blurry underwater becauseyou have a water-cornea boundaryinstead with little difference in n.An eye focuses by changing the focallength of the lens using the ciliarymuscles to change the curvature.This is known as accomodation.Relaxed muscles give a long f ,contracted gives small f .


Vision Defects and Their Correction

The farthest distance a relaxed eye can focus is the far point (FP).The closest is the near point (NP).

The NP changes with age as your lens becomes less flexible. Itmoves from ≈ 25cm to ≈ 200cm by age 60. This is calledpresbyopia.Presbyopia is known as a refractive error of the eye. Otherrefractive errors include myopia and hyperopia. All can becorrected by lenses.Lenses are prescribed by their power

P =1f

The SI unit of power is the diopter (D) (or dioptre) defined in m−1

If you have glasses with P = +2.5D you have a converging lenswith focal length 0.4 m.



The farthest distance a relaxed eye can focus is the far point (FP).The closest is the near point (NP).The NP changes with age as your lens becomes less flexible. Itmoves from ≈ 25cm to ≈ 200cm by age 60. This is calledpresbyopia.

Presbyopia is known as a refractive error of the eye. Otherrefractive errors include myopia and hyperopia. All can becorrected by lenses.Lenses are prescribed by their power

P =1f





The farthest distance a relaxed eye can focus is the far point (FP).The closest is the near point (NP).The NP changes with age as your lens becomes less flexible. Itmoves from ≈ 25cm to ≈ 200cm by age 60. This is calledpresbyopia.Presbyopia is known as a refractive error of the eye. Otherrefractive errors include myopia and hyperopia. All can becorrected by lenses.

Lenses are prescribed by their power

P =1f





The farthest distance a relaxed eye can focus is the far point (FP).The closest is the near point (NP).The NP changes with age as your lens becomes less flexible. Itmoves from ≈ 25cm to ≈ 200cm by age 60. This is calledpresbyopia.Presbyopia is known as a refractive error of the eye. Otherrefractive errors include myopia and hyperopia. All can becorrected by lenses.Lenses are prescribed by their power

P =1f





The farthest distance a relaxed eye can focus is the far point (FP).The closest is the near point (NP).The NP changes with age as your lens becomes less flexible. Itmoves from ≈ 25cm to ≈ 200cm by age 60. This is calledpresbyopia.Presbyopia is known as a refractive error of the eye. Otherrefractive errors include myopia and hyperopia. All can becorrected by lenses.Lenses are prescribed by their power

P =1f




Hyperopia

Hyperopia causes far-sightedness.The FP might be fine, but the NP istoo far away.

The eyeball is too short for therefractive power of the cornea.Add a lens to boost refractive power.A converging lens is needed.The lens should form an uprightvirtual image at the eye’s actual NP.This image then becomes the objectfor the eye.


Hyperopia

Hyperopia causes far-sightedness.The FP might be fine, but the NP istoo far away.The eyeball is too short for therefractive power of the cornea.

Add a lens to boost refractive power.A converging lens is needed.The lens should form an uprightvirtual image at the eye’s actual NP.This image then becomes the objectfor the eye.


Hyperopia

Hyperopia causes far-sightedness.The FP might be fine, but the NP istoo far away.The eyeball is too short for therefractive power of the cornea.Add a lens to boost refractive power.A converging lens is needed.

The lens should form an uprightvirtual image at the eye’s actual NP.This image then becomes the objectfor the eye.


Hyperopia

Hyperopia causes far-sightedness.The FP might be fine, but the NP istoo far away.The eyeball is too short for therefractive power of the cornea.Add a lens to boost refractive power.A converging lens is needed.The lens should form an uprightvirtual image at the eye’s actual NP.This image then becomes the objectfor the eye.


Myopia

Myopia causes near-sightedness.The NP might be fine, but the FPneeds adjustment.

The eyeball is too long for therefractive power of the cornea.Add a diverging lens to fix theproblem.The lens should form an uprightvirtual image at the eye’s actual FP.This image then becomes the objectfor the eye.


Myopia

Myopia causes near-sightedness.The NP might be fine, but the FPneeds adjustment.The eyeball is too long for therefractive power of the cornea.

Add a diverging lens to fix theproblem.The lens should form an uprightvirtual image at the eye’s actual FP.This image then becomes the objectfor the eye.


Myopia

Myopia causes near-sightedness.The NP might be fine, but the FPneeds adjustment.The eyeball is too long for therefractive power of the cornea.Add a diverging lens to fix theproblem.

The lens should form an uprightvirtual image at the eye’s actual FP.This image then becomes the objectfor the eye.


Myopia

Myopia causes near-sightedness.The NP might be fine, but the FPneeds adjustment.The eyeball is too long for therefractive power of the cornea.Add a diverging lens to fix theproblem.The lens should form an uprightvirtual image at the eye’s actual FP.This image then becomes the objectfor the eye.


Modern Optics and Matter Waves (Chapter 25)

We have been studying different physical models for light: thewave model and the ray model.

Chapter 25 of your text gets into the third model: the particlemodel.It turns out that sometimes describing light as a wave or as a raycannot explain its behaviour! Light behaves in very strange wayswhich puzzled physicists for a long time.Until now we have been treating light the way it was treatedpre-1900. Experiments at that time already were challenging theway we thought about light.The greatest technological advances of the 20th century would nothave been possible without a huge leap in our understanding oflight (radiation) and matter...and the birth of Quantum Mechanics.



We have been studying different physical models for light: thewave model and the ray model.Chapter 25 of your text gets into the third model: the particlemodel.

It turns out that sometimes describing light as a wave or as a raycannot explain its behaviour! Light behaves in very strange wayswhich puzzled physicists for a long time.Until now we have been treating light the way it was treatedpre-1900. Experiments at that time already were challenging theway we thought about light.The greatest technological advances of the 20th century would nothave been possible without a huge leap in our understanding oflight (radiation) and matter...and the birth of Quantum Mechanics.



We have been studying different physical models for light: thewave model and the ray model.Chapter 25 of your text gets into the third model: the particlemodel.It turns out that sometimes describing light as a wave or as a raycannot explain its behaviour! Light behaves in very strange wayswhich puzzled physicists for a long time.

Until now we have been treating light the way it was treatedpre-1900. Experiments at that time already were challenging theway we thought about light.The greatest technological advances of the 20th century would nothave been possible without a huge leap in our understanding oflight (radiation) and matter...and the birth of Quantum Mechanics.



We have been studying different physical models for light: thewave model and the ray model.Chapter 25 of your text gets into the third model: the particlemodel.It turns out that sometimes describing light as a wave or as a raycannot explain its behaviour! Light behaves in very strange wayswhich puzzled physicists for a long time.Until now we have been treating light the way it was treatedpre-1900. Experiments at that time already were challenging theway we thought about light.

The greatest technological advances of the 20th century would nothave been possible without a huge leap in our understanding oflight (radiation) and matter...and the birth of Quantum Mechanics.



We have been studying different physical models for light: thewave model and the ray model.Chapter 25 of your text gets into the third model: the particlemodel.It turns out that sometimes describing light as a wave or as a raycannot explain its behaviour! Light behaves in very strange wayswhich puzzled physicists for a long time.Until now we have been treating light the way it was treatedpre-1900. Experiments at that time already were challenging theway we thought about light.The greatest technological advances of the 20th century would nothave been possible without a huge leap in our understanding oflight (radiation) and matter...and the birth of Quantum Mechanics.


X-Ray Diffraction (25.2)

One of the interesting experiments ofthe late 19th century lead to thediscovery of x-rays by Roentgen.

These x-rays were very peculiar.They acted like rays. However, theypenetrated matter. He could notreflect them, diffract them, etc. Theywere not obviously wave-like.Nevertheless, it was speculated thatx-rays were very short-wavelengthwaves.Luckily, people had recentlydiscovered that solids were crystalinearrangements of atoms spaced about1nm apart - a natural diffractiongrating!!



One of the interesting experiments ofthe late 19th century lead to thediscovery of x-rays by Roentgen.These x-rays were very peculiar.They acted like rays. However, theypenetrated matter. He could notreflect them, diffract them, etc. Theywere not obviously wave-like.

Nevertheless, it was speculated thatx-rays were very short-wavelengthwaves.Luckily, people had recentlydiscovered that solids were crystalinearrangements of atoms spaced about1nm apart - a natural diffractiongrating!!



One of the interesting experiments ofthe late 19th century lead to thediscovery of x-rays by Roentgen.These x-rays were very peculiar.They acted like rays. However, theypenetrated matter. He could notreflect them, diffract them, etc. Theywere not obviously wave-like.Nevertheless, it was speculated thatx-rays were very short-wavelengthwaves.

Luckily, people had recentlydiscovered that solids were crystalinearrangements of atoms spaced about1nm apart - a natural diffractiongrating!!



One of the interesting experiments ofthe late 19th century lead to thediscovery of x-rays by Roentgen.These x-rays were very peculiar.They acted like rays. However, theypenetrated matter. He could notreflect them, diffract them, etc. Theywere not obviously wave-like.Nevertheless, it was speculated thatx-rays were very short-wavelengthwaves.Luckily, people had recentlydiscovered that solids were crystalinearrangements of atoms spaced about1nm apart - a natural diffractiongrating!!


X-Ray Diffraction

Most x-rays will be transmitted by asolid, but there may be somereflection too. The reflections shouldobey the law of reflection.

However, there are many parallelplanes of atoms. So, destructiveintereference is setup for all but a fewangles. Those few angles should seeconstructive interference.We could analyze this by looking atthe path-length difference betweenrays reflected from different planes. Ifd is the spacing between planes wehave

2d cosθm = mλ,m = 1,2,3, . . .


X-Ray Diffraction

Most x-rays will be transmitted by asolid, but there may be somereflection too. The reflections shouldobey the law of reflection.However, there are many parallelplanes of atoms. So, destructiveintereference is setup for all but a fewangles. Those few angles should seeconstructive interference.

We could analyze this by looking atthe path-length difference betweenrays reflected from different planes. Ifd is the spacing between planes wehave

2d cosθm = mλ,m = 1,2,3, . . .


X-Ray Diffraction

Most x-rays will be transmitted by asolid, but there may be somereflection too. The reflections shouldobey the law of reflection.However, there are many parallelplanes of atoms. So, destructiveintereference is setup for all but a fewangles. Those few angles should seeconstructive interference.We could analyze this by looking atthe path-length difference betweenrays reflected from different planes. Ifd is the spacing between planes wehave

2d cosθm = mλ,m = 1,2,3, . . .Neil Alberding (SFU Physics) Physics 121: Optics, Electricity & Magnetism Spring 2010 7 / 9

X-Ray Diffraction

x-ray diffraction has proved incredibly usefulin understanding the structure of matter.

Place an unknown crystal in the x-ray beamand measure the reflected intensity to learnabout its structure.People in the SFU physics department todayrun x-ray diffraction machines to study theproperties of materials.The invention of a tool to look at the crystalstrucure of matter is important. Furthermore,nature gives us pre-fabricated diffractiongratings for very small wavelengths.


X-Ray Diffraction

x-ray diffraction has proved incredibly usefulin understanding the structure of matter.Place an unknown crystal in the x-ray beamand measure the reflected intensity to learnabout its structure.

People in the SFU physics department todayrun x-ray diffraction machines to study theproperties of materials.The invention of a tool to look at the crystalstrucure of matter is important. Furthermore,nature gives us pre-fabricated diffractiongratings for very small wavelengths.


X-Ray Diffraction

x-ray diffraction has proved incredibly usefulin understanding the structure of matter.Place an unknown crystal in the x-ray beamand measure the reflected intensity to learnabout its structure.People in the SFU physics department todayrun x-ray diffraction machines to study theproperties of materials.

The invention of a tool to look at the crystalstrucure of matter is important. Furthermore,nature gives us pre-fabricated diffractiongratings for very small wavelengths.


X-Ray Diffraction

x-ray diffraction has proved incredibly usefulin understanding the structure of matter.Place an unknown crystal in the x-ray beamand measure the reflected intensity to learnabout its structure.People in the SFU physics department todayrun x-ray diffraction machines to study theproperties of materials.The invention of a tool to look at the crystalstrucure of matter is important. Furthermore,nature gives us pre-fabricated diffractiongratings for very small wavelengths.


X-ray Diffraction

It is by means of x-ray diffractionthat we are able to determine thestructures of protein moleculessuch as rhodopsin


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