Achromatic Aberrations Flashcards
“______ limited” system is considered to be perfect
diffraction-limited system
what can diffraction limit?
it ultimately limits the quality of an optical system, even if there is no scatter or aberrations and the system is in focus
2 types of aberrations
monochromatic and chromatic
for axial points the wavefront aberration has only one component, which is :
spherical aberration
for off-axis points there may be one or more additional components, including:
- coma
- oblique astigmatism
- curvature of field
- distortion
rays from outside the paraxial zone form a:
rather large “blur patch” around the paraxial focus, P’
what is the smallest blur patch called and what is it analogous to?
the “waist” or “clc”, it is analogous to the circle of least confusion
what is special about “fast” optical systems with a wide field of view?
they must be of high precision and such systems are object distant dependent
what is a drawback of the precise “fast” optical systems
if designed to be aberration-free for distant objects, aberrations will be present for a near object, and vice versa
what are other names for the “5 components resulting from the 3rd order term of the sine expansion”?
Seidel aberrations, primary aberrations, 3rd order aberrations, or aberrations of form
all aberrations are _____ ______ dependent
object distance (x)
what type of aberration would be important in spectacle lenses and why?
oblique aberrations are important since the eye may rotate and look obliquely through the lens
what types of aberrations wouldn’t be as important in spectacle lenses and why?
aberrations that are aperture-dependent are small and of less importance because the aperture of these lenses is effectively limited by the pupil
are the monochromatic aberrations in the eye small or large and why?
monochromatic aberrations of the eye are rather small, especially if the diameter of the pupil also is small
Δω= magnitude of
magnitude of the transverse aberration
Δω is the distance between:
point where the actual ray crosses the paraxial image plane and the paraxial image point
y=
the distance of the object point from the optical axis
ρ= the ___ _____
zone radius
ρ, the zone radius, is the distance of:
the distance of the ray from the center of the entrance pupil
C30 ρ^3 =
spherical aberration
C21 ρ^2 y =
coma
C12 ρ y^2 =
oblique astigmatism
D12 ρ y^2 =
curvature of field
C03 y^3 -
distortion
spherical aberration depends only on the:
zone radius (ρ)
spherical aberration applies to what type of axis points?
both on and off axis object points
ls / ts =
xs’ / ρ
in SA, the peripheral ray crosses the optical axis at a distance ___ from the paraxial focus
ls
the term ( ls ) stands for
longitudinal spherical aberration for a ray
in SA, the distance of the ray from the paraxial focus as it crosses the paraxial image plane is called ____
ts
the term ( ts ) stands for
the transverse spherical aberration
if the object is a single point on the optical axis, then all of the primary aberrations are zero except ______
spherical aberrations (SA)
longitudinal SA may be expressed in dioptric form as
(1/xs’) - (1/x)
xs’ = the distance from….
the distance from the lens to the point where the peripheral ray crosses the OA
u= shape factor =
(r2 + r1) / (r2-r1)
v= position factor =
(x’ + x) / (x’ - x)
what is the term “lens bending” used to do?
lens bending is a term used to denote the selection of an optimum lens shape (surface radii) while holding lens power fixed
what is the shape factor for plano-convex, equiconvex, and convex-plano?
plano-convex: u= -1
equiconvex: u=0
convex-plano: u= +1
what would the ratio of surface radii (r2/r1) value for a lens that minimizes SA for a distant object?
about -6
shape that best minimizes SA for a distant object is
a biconvex shape close to a convex-plano shape
shape that best minimizes SA for an image at infinity (near object)
close to a plano-convex
the principle behind fining an optimum lens shape is: the SA for a lens or system of lenses is minimizes by causing ……
by causing deviations to be equally divided between the surfaces
the maximum SA when the EP and AS are the same for a single thin lens is proportional to:
the square of the AS diameter
the Δω for coma is:
Δω= C21 ρ^2 y
since coma is zero for on-axis image points (y=0)… coma only affects what kind of image points?
only affects off-axis image points
describe what it means by ‘coma has a fairly strong dependence on zone radius’
the rays through the lens periphery will be aberrated much more than rays near the center of the lens
describe coma
for off-axis pencils, rays passing through peripheral zones of the lens will come to a focus at points laterally displaced from rays through more central zones of the lens
the lens shape that causes coma to be zero is
close to the lens shape that minimizes SA
when an object is at infinity, the shape factor (u) that minimizes coma is:
about -9
what are the two aberrations that are proportional to y^2ρ
oblique astigmatism and curvature of image
in oblique astigmatism, what are the orientations of the line foci in the conoid of sturm dependent on?
they depend on the orientations of the tangential and sagittal planes and the orientations of these planes depend on the position of the off-axis object point
the TLF is defined as
the tangential line focus is perpendicular to the tangential plane
the SLF is defined as
the sagittal line focus is perpendicular to the sagittal plane
list the Dt, Dsg and D values in order from greatest to least
Dt > Dsg > D
(TLF or SLF)
the ____ is always closer to the lens than the _____ and both are closer than the paraxial focus
the TLF is always closer to the lens than the SLF
an extended object presented to an optical system with no aberrations except curvature of field would be brought to focus how?
on a curved surface rather than a plane surface
the power Dt and Dsg give the ____ of the line foci but tell us nothing about the ____ of the line foci
positons
lengths
the lengths of the line foci are directly proportional to the
lens aperture diameter
oblique astigmatism may be reduced by the choices of the:
convergent and divergent surfaces (front and back curves) of a spectacle lens
the Δω for distortion is
C03 y^3
distortion depends only on the:
distance of the object from the OA
which aberration has no dependence on zone radius (aperture size)?
distortion
explain distortion
the lateral magnification of an image either increases or decreases as one moves off-axis
how does distortion affect shape and/ or blur of an image?
the shape of the image may differ from that of the object, but imagery is sharp- distortion is not blur or loss of resolution
