L10 - stops and pupils

Question 1

What effect does the physical size of lens have on an image? - without changing power of the lens

Answer 1

• The larger the lens will allow more light through the optical system and reach the image hence the image is brighter
• Lens type remains the same: same radius of curvature, same thickness, same material- lenses will have identical power and cardinal points.

Question 2

What is used to change the size of beam of light going through without having to change the lens?

Answer 2

-Stops are used: opaque, black screens with ca central hole and can adjusted accordingly to desired size.

Question 3

What is the effect of placing a stop before the lens?

Answer 3

we reduce the aperture of the lens in the same way as if we had a small lens.

Question 4

When placing stop what happens?

Answer 4

-It has the same effect as placing a small lens - you can see central rays getting through.

Question 5

What happens when the stop (diaphragm) is placed in different places ?

Answer 5

• The bottom half of the beam- this leads to aberrations- which degrade the image
• By placing in different places can effect the amount of light and also quality of image

Question 6

What happens if stop is placed badly?

Answer 6

prevent an image from being formed at all

-None of the light making through the aperture, makes it through the Len s- misses lens completely.

Question 7

What do stops affect?

Answer 7

size and location affect the type of image we get.

Question 8

What else is a lens?

Answer 8

aperture which is defined by its diameter

-lens with a larger diameter has a larger aperture compared to a. small lens,.

Question 9

What is the telescope configuration explained diagram?

Answer 9

• the first set of black rays go through the whole system due to the geometry of the system the power of lenses, focal point of 2nd lens is closer to the 2nd lens, this means all the rays go through this lens and the lens is larger than the beam.
• The top and bottom od second lens is redunadant

Question 10

What is an aperture?

What is a stop?

Answer 10

Aperture is any clear region of optical surface through which light can be transmitted
-a stop is an opaque structure

Question 11

What is an aperture stop?

Answer 11

defines the aperture of the optical system as a whole defines the largest cone off light that can be transmitted by the optic lssytem.

Question 12

What can optical systems have?

Answer 12

only 1 aperture stop

-But can have many apertures or elements.

Question 13

What is a limiting aperture ?

Answer 13

-When all the rays do not go through the lens. - hence serves as the aperture of the system.
A.S- determines how much light goes through the whole system

Question 14

What can you do in an optical system?

Answer 14

-Add apertures e.g 2 lenses and 2 stops.

Question 15

What exit pupil?

Answer 15

the region where light leaves the optical system.

Question 16

To find where the aperture stop is , how dow e determine the largest beam of light that can go into our system?

Answer 16

-can use a Imaginary pupils

Question 17

What is entrance pupil ?

Answer 17

the region where the light enters the system

Question 18

When we deal with stops and apertures what do we use?

Answer 18

entrance and exit

Question 19

When we deal with cardinal point and priucipoal planes, what do we use?

Answer 19

object space and image space.

Question 20

What is the chief ray?

Answer 20

the ray that goes through the aperture stop- middles of beam, of light

Question 21

What are the off axis marginal rays?

Answer 21

the extreme rays that are above and below the aperture stop.

Question 22

Why do we need to draw the construction rays for the entrance and exit pupil diagram first?

Answer 22

• Once you find out the inane locationn you can then find out the largest beam - form looking at the entrance side the chief ray extends until it crosses the optical axis- which tells us where the entrance pupil is
• if you extend the off axis marginal rays this will tell where the extremes of the entrance pupil is.

Question 23

How do you find the entrance pupils?

Answer 23

form looking at the entrance side the chief ray extends until it crosses the optical axis- which tells us where the entrance pupil is

• if you extend the off axis marginal rays this will tell where the extremes of the entrance pupil is.
• It is a imaginary dashed line line.

Question 24

How dow e represents entrance pupil and exit pupil?

Answer 24

via imaginary dashed lines E and E’- to remind us that they are not real.

Question 25

What is an entrance pupil?

Answer 25

looking at the the entrance and not see aperture stop , you see an image
-the aperture limiting how much light goes through the system./

Question 26

How do you determine the size of the entrance/exit pupil?

Answer 26

extend the marginal rays

Question 27

How do you determine the position of the entrance/exit pupil?

Answer 27

extend the chief ray until it crosses the optical axis.

Question 28

What are the rays going towards the edges of the entrance pupil?

Answer 28

the largest cone of light leaving the object the can go through the system

Question 29

What is meant by object image pairs?

Answer 29

c

Question 30

What is meant by object image pairs?

Answer 30

c

Question 31

What is the case study?

Answer 31

The human eye- entrance an de exit pupil
-The iris is the aperture stop of the eye - and nits diameter changes depending on the hewing conditions and other factod

Question 32

What happens when we looki into the eye?

Answer 32

We see the image of the iris formed by the cornea which is infront of the iris.

• we see entrance pupil hence the name pupil
• Dont have access to iris so can find entrance pupil fo eye .

Question 33

What is the location of the pupil ?

Answer 33

is the eyes entrance pupil- black circle

• the outside world is seen at the point at the centre of the entrance pupil
• the pupil itself (aperture) is in a slightly different location because the image is magnified by the cornea.