Week 2

Question 1

Depth of focus

Answer 1

• the interval surrounding the retina where an eye sees and object in focus
• behind the eye

Question 2

Depth of field

Answer 2

The interval surrounding the fixation plane where an object will still be in focus and there will be no perceivable blur on the retina
-out in space

Question 3

Focal ratio

Answer 3

-f number/f-stop/ f/stop
Focal length/diameter of aperture
-diopters

Question 4

Trends of focal ratio

Answer 4

• shorter focal length gives a larger depth of field
• increase in aperture size leads to decreased depth of field and decreased depth of focus
• larger f/stop: fewer aberrations, larger depth of focus
• smaller f/stop: gives brighter image, narrows focus

Question 5

Hyperfocal distance

Answer 5

A distance at which a camera or system is focused so that the distal limit of the depth of field is at optical infinity

Question 6

Depth of field trends

Answer 6

• increase in f-stop(decrease in aperture size) = larger depth of field
• decrease in f/stop(increase in aperture size)= smaller depth of field

Question 7

Computation of geometrical blur size

Answer 7

Blur(mad)=defocus X pupil size in mm

Blur(minutes)= 3.44 X D X pupil size in mm

Question 8

Small pupil advantage

Answer 8

Increase the depth of focus and decrease the blur, compensate for loss of accommodation in old age
-better night vision

Question 9

Methods for reducing pupil size

Answer 9

Artificial pupil, artificial iris, moo tic agent

Question 10

Disadvantage of adding just adding an artificial pupil

Answer 10

Decreased field of view!

-creates an additional field stop or aperture stop

Question 11

parallel wavefront

Answer 11

-collimated light

Question 12

spherical wavefront

Answer 12

• converging light beam

- diverging light beam

Question 13

Wave aberration

Answer 13

• the deviation of a wavefront in an optical system from a desired prefect planar wavefront
• away from the predictions of the paraxial optics

Question 14

aberrations

Answer 14

• failure for the light rays passing through an optical system to converge at one point
• possibly due to defects or limitations of the system

Question 15

first order aberrations

Answer 15

• piston (move the whole thing up or down)

- tilit(the plane is tipped in one direction)

Question 16

Second order aberrations

Answer 16

• defocus (spherical correction)

- astigmatism(cyl correction)

Question 17

higher order aberrations

Answer 17

Most common: spherical then coma

Question 18

Zernike polynomials

Answer 18

-set of basic shapes that are used to fit the wavefront

Question 19

Properties of zernike polynomials

Answer 19

• orthogonal(terms are not similar so they can be separated and looked at individually)
• normalized( sum of vectors)
• efficient(shapes are similar to typical aberrations found in the eye)

Question 20

strum’s interval

Answer 20

-the difference between the focal points(points of focus) of each meridian

Question 21

Circle of least confusion

Answer 21

-point between the points of focus of the two meridians where each meridian is equally burred

Question 22

spherical aberration

Answer 22

-only aberration that occurs for both on-axis and off-axis object points

Question 23

Positive spherical aberration

Answer 23

-peripheral rays intersect closer to the lens that central

Question 24

Negative spherical aberration

Answer 24

-peripheral rays intersect after the central rays

Question 25

prolate ellipse

Answer 25

-more curved in the center

Question 26

oblate ellipse

Answer 26

-more curved at the top

Question 27

coma aberration

Answer 27

• comet shaped pattern caused by off-axis point source passing through a spherical system
• associated with kertaconus

Question 28

pilots have more what?

Answer 28

-vertical coma

Question 29

oblique/marginal/radial astigmatism

Answer 29

• off axis light coming through cylindrical system

- glasses that bend around your face and not flat can induce this

Question 30

recognize barrel and pincushion distortino

Answer 30

-barrel is rounded and pincushion is flatter

Question 31

rayleigh resolution limit

Answer 31

• limit distance so that you still have two dots

- between resolved and unresolved point sources

Question 32

minimum angle of resolution and pupil size relation

Answer 32

-smaller pupil means larger min angle means worse resolution

Question 33

what is the idea pupil size?

Answer 33

2mm

Question 34

diffraction

Answer 34

-causes light to bend perpendicular to the direction of the diffracting edge

Question 35

interferene

Answer 35

causes the diffracted light to have peaks and valleys

Question 36

airy disk

Answer 36

• light through circular aperture results in this

- description of the best focused spot of light that a perfect lens can make, limited by diffraction of light

Question 37

what is the one limitation of the image quality of an optical system?

Answer 37

-diffraction limit