Ch. 3 - Optical Instrumentation Flashcards
aperture
in its broadest sense, is an opening defined by a geometrical boundary.
______ 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.
Apertures - always a physical component
Apertures mitigate effects of:
3 effects + added features
spherical aberration
astigmatism
distortion
as well as produce a sharp border to image; or shield image from undesirable light
apertures inevitably present because…
every lens or mirror has a finite diameter that effectively introduces an aperture into the system.
Adding an aperture influences image-forming properties by two distinct mechanisms:
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
Does aperture control intensity?
No. Aperture controls flux–“brightness”
Apertures determine (or can be, in some situations)….
…determine the entrance or exit pupil
In Macaluso Physics, Aperture stop….
limits the cone of light entering an optical system and, as a result, limits the size of the object.
In real physics, Aperture stop…
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.
In a telescope the objective lens is…
…the aperture stop of the optical system
Aperture stop is/is not always the first component of an optical system.
Is not! Sometimes, the lens rim can be the limiting aperture.
The entrance pupil…E(n)P
….the limiting aperture (opening) that the light rays “see,” looking into the optical system from any object point
effective aperture due to the A.S. is its…
image formed by lens.
Exit Pupil….E(x)P
…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).
Chief/Principal Ray
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.
Field of View of system:
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.
vignetting
partial shielding of the outer portion of the image by the aperture for off-axis object points is called
Field Stop
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.
Entrance Window
The entrance window is the image of the field stop formed by all optical elements preceding it
Exit Window
The exit window is the image of the field stop formed by all optical elements following it.
Aperture stop AS:
Controls?
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.
Entrance pupil EnP:
Controls?
Controls Brightness
The image of the aperture stop formed by the optical elements (if any) that precede it.
Exit pupil ExP:
Controls?
Controls Brightness
The image of the aperture stop formed by the optical elements (if any) that follow it.
Field stop FS:
Controls?
Controls Field of View
The real element that limits the angular field of view formed by an optical system.
Entrance window EnW:
Controls?
Controls Field of View
The image of the field stop formed by the optical elements (if any) that precede it.
Exit window ExW:
Controls?
Controls Field of View
The image of the field stop formed by the optical elements (if any) that follow it.
Six types of Aberrations
1) Chromatic
2) Spherical
3) Coma
4) Astigmatism
5) Curvature of Field
6) Distortion
Aberrations occur largely as a result from…
…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
results because the index of refraction of a material differs for different wavelengths
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.
Distortion
image is an unfaithful representation of the object
aberrations, vignetting, etc
introducing apertures has good/bad effects:
good: image is more accurate
bad: limiting photon at the expense of FoV and brightness
