Chapter 27 Optical instruments

distant objects in relation to focal point

- F is greatest - ciliary muscles are relaxed

Near objects in relation to focal length

- F is shortened - tensed ciliary muscles - lens shape altered

Angular magnification, M

M = @'/@ M = (ho/f)/(ho/N) = N/f

a biologist with a near point distance of N= 26 cm examines an insect wing through a magnifying glass whose focal length is 4.3 cm. Find the angular magnification when the image produced by the magnification is (a) at infinity and (b) at the near point

M = N/f = 26cm/4.3 cm = 6.0 1/do = 1/f - 1/di = 1/4.3 - 1/-26 cm = 0.27 cm^-1 do = 3.7cm M = N/do = 26cm/3.7cm = 7.0

Pinhole camera

the image is upside down. of hole is sufficiently small, each point on the image corresponds one point on the object

the aperture of camera controls?

the amount of light

Why don't things look upside down to us?

the brain adjusts the image to appear properly

which of the following statements is true about an eye that is nearsighted?

- the image is in front of the retina, and this can be corrected by a diverging lens

f-numbers

1.4, 2, 2.8, 4, 5.6, 8, 11

shutter speeds: s

1/1000s 1/500 s 1/250 s 1/30 s etc

if these glasses are used to view an object 525cm from the eye, how far from the eye is the image produced by a concave lens?

1/do + 1/di = 1/f di = do x f/(do-f) di = (523)(-321)/(523-(-321) di = -198.9 cm from eye +2 = 201 cm

refractive power =

1/focal distance si unit: diopeter= m^-1

a nearsighted person has a far point that is 323 cm from her eye. if the lens in a pair of glasses is 2cm in front of her eyes, what focal length must it have to allow her to focus on distant objects? - use thin lens equation

1/inifinity + 1/(-321) = 1/f f = 321 cm

the -5 diopter lens is used for a man using glasses 2 cm from his eyes. what is the distance to the far point for him using these lenses?

22cm 1/di = 1/f - 1/do = 1/-20 - 1/0 di = -20cm. as lens is 2 cm from the eye the far point is 20+2 = 22cm

people with normal vision, it is about _________ cm from the eye but increases with age as the lens becomes less flexible

25

2 brothers, Frank and Nathan, go camping and want to start a fire. Frank is farsighted and Nathan is nearsighted. it is sunny outside. which brother's glasses can focus the sun's light to start a fire?

Frank's a lens used for farsighted is a convex (converging) lens, which can be used to focus the rays of the sun to start a fire

___________ and _________ on the retina convert light into electrical impulses, which travel down the optic nerve to the brain

Rods, Cones

corrective optics for farsightedness

a converging lens is used to augment the converging power of the eye. the final image is past the near point

corrective optics for nearsightedness

a diverging lens is used. its focal length is such that a distant object forms an image at the far point

a magnifying glass

a simple convex lens working in conjunction with the eye, making objects appear many times bigger than their actual size - it allows objects to be viewed from a short distance and this makes them appear larger

the ciliary muscles adjust the shape of the lens to ___________ near and far vision. they change its focal length

accommodate

shutter speed also controls the _________________ falling on the film

amount of light

the combination of f-number and shutter speed determines the ______________ that reaches the film

amount of light

If you thought of the eye as having an f-number, how does it increase it?

by relaxing the ciliary muscles or contracting the iris

nearsightedness (Myopia)

can see close objects but not far away

Farsightedness (hyperopia)

can see distant objects clearly but cannot focus on close objects - the near point is too far away the lens of the eye is not strong enough and the image focus is behind the retina

The _______________ change the shape of the lens, so it can focus at different distances

ciliary muscles

the camera lens cannot change in shape (as compared to the eye); it moves _________ to or ___________ from the film in order to focus

closer to or further

large telescopes?

collects as much light as possible

a compound microscope has, in its simplest form, 2 _______________ lenses. One, the _________ is close to the eye while the ___________ is close to the object

converging, eyepiece, objective

Light passes through the ______________________________ and is focused by the lens on the retina

cornea of the human eye

if the iris contracts, it will __________ the diameter of the pupil

decrease

Mtotal =

m(objective) x M(eyepiece) = (-di/f(objective)(N/feyepiece) = diN/f(objective)feyepiece

the image formed is __________ and ______________ at the focal point of the eyepiece which produces a _____________ image at infinity (acts like a magnifier)

enlarged, inverted, virtual

a person has a far point that is 5.5m from his eyes. if this person is to wear glasses that are 2cm from his eyes, what refractive power, in diopters must his lens have? - do = infinity - di = -548cm - f = -548cm

f = di = -548cm RP = 1/f = 1/-5.48m = -0.182 diopter

find the focal length of a pair of contact lenses that will allow a person with near point distance of 145cm to read a newspaper held 25.1 cm from the eyes - do = 25.1 cm - di = -145 cm - f = 30.4 cm

f = dodi/(do+di) =(-145 cm)(25.1 cm)/(-145 cm+25.1 cm) = 28.6 cm - note that the image distance is negative since the image is on the same side of the lens as the object

f-number characterizes the size of the aperture

f-number = focal length/ diameter of aperture f- number = f/D

the _____________ is the farthest point at which the eye can focus; it is _____________ if vision is normal

far point, infinitely far away

a nearsighted person has a far point that is a _______ distance away, objects farther away will appear _________. this is due to the lens focusing too strongly so the image is formed in _________ of the retina

finite (not infinity), Blurry, in front

telescopes are similar to microscopes but the light will be focused at the _______________of the objective

focal point - the objects themselves are very large, but their angular size is very small due to their great distance

relaxing the ciliary muscle will __________ the focal length of the lens

increase

either increasing f or decreasing the diameter, D, will ___________ the f-number of the eye

increase f-number =f/D

A camera's f-number is reduced from 2.8 to 1.4. what factor is the light entering the camera (the exposure) changed, assuming the shutter speed is unchanged?

increased by a factor of 4 - decreasing the f-number a factor of 2 will increase the diameter by a factor of 2. this will increase the area through which light enters by a factor of 4. thus increase the exposure by a factor of 4

Amount of light entering the eye is controlled by ________________ through the pupil

iris

if the focal lengths of both the objective lens and the eyepiece were doubled in a compound microscope, what would be the change in the magnification?

it would decrease - increasing both focal lengths will decrease the magnification Mtotal = -diN/f(objective)f(eyepiece)

The smaller the f-number the ____________ the D and the area

larger

place a converging lens whose focal length is less than N very close to the eye and the place the object at the focal point of the lens. this gives you the object a ______________

larger angular size

A simple camera consists of

lens and film in a light tight box

the object is placed near the focal point of the objective lens, giving a magnification of:

m(objective) = -di/do = di/ f(objective)

the ____________ is the closest point to the eye that the lens is able to focus.

near point

chromatic abberation

occurs when different colors of light focus at different

Spherical abberation

occurs when light striking the lens far from the axis does not focus properly - it can be fixed by grinding the lends to a precision, non - spherical shape

the eye produces a ________ , ____________ image on the retina

real, inverted

the strength of corrective lenses is usually quoted a __________________, which is the inverse of the focal length

refractive power

telescopes using lenses are called _________-; using the first telescope made were of this type

refractors

the angular size of an object is the angle it subtends on the ___________ and depends both on the ___________ of the object and its _________ from the eye

retina, size, distance θ = ho/do

total magnification of the telescope is?

the product of the magnification of each lens M = @/@' = f(objective)/f(eyepiece)

total magnification

the product of the magnifications of each lens mtot = m1xm2

the _____________ and _____________ humors are transparent

virteous, aqueos

entering light

~ A ~ D^2 ~ 1/fn^2 number