Chromatic Aberration
Distortion
- Image is not blurred but it is distorted - Caused by the presence of a stop (aperture) in a system known as?
pincushion distortion (+ power in front of an aperture)
A cornea and pupil produces what type of distortion?
pincushion distortion (Plus power in front of the pupil)
A corrected hyperope may experience what type of distortion?
barrel distortion (Minus power in front of the pupil)
A corrected myope may experience may experience what type of distortion?
A chromatic Doublets
A plus and minus lens put together such that the positive CA of one lens combines with the negative CA of the other lens to eliminate most, but not all CA
barrel distortion (aperture in front of a plus lens)
A pupil and crystalline produces what type of distortion?
q = 0.7-0.8
A shape that has a q-value of blank will minimize coma
monochromatic aberrations aka Seidel aberrations
Aberrations CAN still occur with monochromatic light, and these are known as
False
An aberration is from a scratch, or a defect, or a distortion in the lens
applanatic
An optical system which is free of both spherical aberration and coma is said to be?
Abbe number
Another name for Constringency and Refractive efficiency is
Paraxial Assumption
Assuming that all light traveling through a lens is close to the optical axis will come to a focal point is known as
duochrome/bichrome test (sphere check)
CA in the eye is the basis for what test
False
Chromatic aberration is not also known as dispersion
the image plane (the film plane) is flat
Curvature of field is an aberration of considerable concern in the design of a camera lens because?
Minimizes... The retinal surface is curved like the image surface - this minimizes curvature of field in the eye
Does curvature of field abberation in the eye increase or minimizes and why?
shape factor. Every lens has a "shape factor" that defines its shape.
Every lens has a "shape factor" that defines its shape. What formula is this?
plus
If a patient reports "the green side is clearer" what sign do we add more of?
minus
If a patient reports "the red side is clearer" what sign do we add more of?
green
If you can't achieve an endpoint of "equal"...When you're stuck between 2 lenses, select the choice of what color?
Lateral Chromatic Aberration
Lateral spread on a screen measured in prismatic differences in image size. Chromatic difference in magnification
Longitudinal CA
Lens Power / Dispersive Constant same as Lens Power / Abbe Number
Longitudinal CA
Lens Power x Dispersive Power
True
Light goes through a correctly powered spectacle but fails to form a perfect image because every object point is not imaged as a point
Longitudinal Chromatic Aberration
Longitudinal distance between blue and red focal points on the optical axis. The distance can be described by dioptric (D) or linear (cm or mm) value
small
Paraxial rays form what size blur circle?
big
Peripheral rays causes what size blur circle?
180 (- cyl x 180)
Rotating a minus lens about the 180 axis (pantoscopic/retroscopic tilt) induces minus cylinder with what axis?
090 (- cyl x 090)
Rotating a minus lens about the 90 axis(positive/negative face form) induces minus cylinder with what axis?
180 (+ cyl x 180)
Rotating a plus lens about the 180 axis (pantoscopic/retroscopic tilt) induces plus cylinder with what axis?
090 (+ cyl x 090)
Rotating a plus lens about the 90 axis (positive/negative face form) induces plus cylinder with what axis?
True
Since each wavelength making up white light "sees" a different refractive index, each wavelength will focus at a slightly different location
True
T/F chromatic aberration happen bc of different wavelengths focusing at different locations
True
T/F CA reduces VA
True
T/F High ν = High Abbe = less chromatic aberration
False
T/F High ν = More chromatic aberration
True
T/F Higher index materials typically have more chromatic aberration
False
T/F Lower Abbe = better VA
False
T/F Refractive index is a constant and not wavelength-dependent
True
T/F When dispensing for low abbe lenses Keep the lenses small
True
T/F find a frame that fits! Pupils should be reasonably centered in the frame, especially for higher Rx
False
T/F greater difference between red and blue focus = lower dispersive power
curvature of field
The fishbowl effect is due to?
secondary spectrum
The remaining chromatic aberration after an achromatic doublet is used is called
apochromatic lens
Using a triplet lens would focus all 3 wavelengths at the same position known as an
Fishbowl effect - Patients complain that they feel like they are in a fishbowl
Wearing spectacle lenses with base curves that are too steep, especially high plus lenses, can create?
The pupil
What anatomical structure controls abberation?
The induced cylinder power
What formula is this?
The new sphere power of a tilted frame
What formula is this?
aspheric lens
What lens gets flatter along the periphery and can also minimize abberation?
Longitudinal Spherical Aberration
What type of abberation is this?
Spherical blur circles
a series of blur circles of different sizes superimposed on top of each other like pancakes is known as?
"f-line" = nF
index seen by blue
"c-line" = nc
index seen by red light
"d-line" = nD
index seen by yellow
True
n = λair / λmaterial, n is higher for shorter wavelengths (denominator goes down)
Petzval surface
peripheral rays striking a lens will bend more - Because of this, they focus sooner The axial rays focus later because they don't bend as much As a result, we get a curved image surface known as the?
Comatic Aberration (or "Coma")
spherical aberration that occurs when the object is not sitting on the optical axis is known as?
Dispersive Constant
v = 1/w or v = 1/Dispersive Power
q = +0.7
what is the q value for the least spherical aberration?
Pincushion Distortion
when the limiting aperture is either Behind a plus lens In front of a minus lens
Barrel Distortion?
when the limiting aperture is either In front of a plus lens Behind a minus lens
Lateral Chromatic Aberration
y(cm) x D x w
yes
yes/no Will sending a monochromatic light through a lens eliminate all other abberations?
