Ch. 3 - Optical Instrumentation

Question 1

aperture

Answer 1

in its broadest sense, is an opening defined by a geometrical boundary.

Question 2

______ can be used to modify the effects of spherical aberration, astigmatism, and distortion.

In addition, may be introduced to produce a sharp border to the image, like the sharp outline we see looking into the eyepiece of an optical instrument and shield image from undesirable light.

Answer 2

Apertures - always a physical component

Question 3

Apertures mitigate effects of:

3 effects + added features

Answer 3

spherical aberration
astigmatism
distortion

as well as produce a sharp border to image; or shield image from undesirable light

Question 4

apertures inevitably present because…

Answer 4

every lens or mirror has a finite diameter that effectively introduces an aperture into the system.

Question 5

Adding an aperture influences image-forming properties by two distinct mechanisms:

Answer 5

1) limits the field of view
2) controls image brightness (irradiance)
forget intensity– use flux (photon/sec)(1/Area)

blue vs. red light, for example, higher/lower E per photon

Question 6

Does aperture control intensity?

Answer 6

No. Aperture controls flux–“brightness”

Question 7

Apertures determine (or can be, in some situations)….

Answer 7

…determine the entrance or exit pupil

Question 8

In Macaluso Physics, Aperture stop….

Answer 8

limits the cone of light entering an optical system and, as a result, limits the size of the object.

Question 9

In real physics, Aperture stop…

Answer 9

The aperture stop of an optical system is the actual physical component that limits the size of the maximum cone of rays—from an axial object point to a conjugate image point that can be processed by the entire system.

Question 10

In a telescope the objective lens is…

Answer 10

…the aperture stop of the optical system

Question 11

Aperture stop is/is not always the first component of an optical system.

Answer 11

Is not! Sometimes, the lens rim can be the limiting aperture.

Question 12

The entrance pupil…E(n)P

Answer 12

….the limiting aperture (opening) that the light rays “see,” looking into the optical system from any object point

Question 13

effective aperture due to the A.S. is its…

Answer 13

image formed by lens.

Question 14

Exit Pupil….E(x)P

Answer 14

…the image of the A.S. one sees by looking into the optical system from the object

…the image of the controlling aperture stop formed by the imaging elements following it (or to the right of it in our figures).

Question 15

Chief/Principal Ray

Answer 15

The chief, or principal, ray is a ray from an object point that passes through the axial point, in the plane of the entrance pupil.

Question 16

Field of View of system:

Answer 16

The controlling element in this connection is called the field stop, and it is related to an entrance window and an exit window in the same way that the aperture stop is related to entrance and exit pupils.

Question 17

vignetting

Answer 17

partial shielding of the outer portion of the image by the aperture for off-axis object points is called

Question 18

Field Stop

Answer 18

The field stop is the aperture that controls the field of view by limiting the solid angle formed by chief rays. As seen from the center of the entrance pupil, the field stop (or its image) subtends the smallest angle.

Question 19

Entrance Window

Answer 19

The entrance window is the image of the field stop formed by all optical elements preceding it

Question 20

Exit Window

Answer 20

The exit window is the image of the field stop formed by all optical elements following it.

Question 21

Aperture stop AS:

Controls?

Answer 21

Controls Brightness

The real element in an optical system that limits the size of the cone of rays accepted by the system from an axial object point.

Question 22

Entrance pupil EnP:

Controls?

Answer 22

Controls Brightness

The image of the aperture stop formed by the optical elements (if any) that precede it.

Question 23

Exit pupil ExP:

Controls?

Answer 23

Controls Brightness

The image of the aperture stop formed by the optical elements (if any) that follow it.

Question 24

Field stop FS:

Controls?

Answer 24

Controls Field of View

The real element that limits the angular field of view formed by an optical system.

Question 25

Entrance window EnW:

Controls?

Answer 25

Controls Field of View

The image of the field stop formed by the optical elements (if any) that precede it.

Question 26

Exit window ExW:

Controls?

Answer 26

Controls Field of View

The image of the field stop formed by the optical elements (if any) that follow it.

Question 27

Six types of Aberrations

Answer 27

1) Chromatic
2) Spherical
3) Coma
4) Astigmatism
5) Curvature of Field
6) Distortion

Question 28

Aberrations occur largely as a result from…

Answer 28

…the form and shape of lenses and mirrors and as a result of rays from an object point striking spherical surfaces at angles that exceed those set by the paraxial approximation

Question 29

results because the index of refraction of a material differs for different wavelengths

Answer 29

Chromatic aberration

*polychromatic light from a point object images not as a point but as a series of points, one for each distinct wave- length.

Question 30

Distortion

Answer 30

image is an unfaithful representation of the object

aberrations, vignetting, etc

Question 31

introducing apertures has good/bad effects:

Answer 31

good: image is more accurate
bad: limiting photon at the expense of FoV and brightness