Corrected Curve Lens Design Flashcards
periscopic lens has a _ BACK curve
-1.25
meniscus lenses have a _ FRONT curve
+6.00
a _ design has a specific base curve to minimize aberrations
corrected curve lens
chromatic aberrations occur due to: _
abbe number/lens material
The 5 aberrations that occur when viewing peripheral objects are called?
Seidel (3rd order)
What aberrations are experienced when peripheral rays focus @ different location than paraxial rays?
spherical aberrations
What are the only aberrations that occur with points on the optic axis?
spherical aberrations
What aberrations occur due to difference in image distance of off axis locations?
coma
What aberrations occur when off axis light passes through spectacle lenses at an angle?
radial/oblique astigmatism (RA)
What aberrations occur when the location of off-axis image points do not match the screen location?
curvature of field
What aberrations occur due to changes in magnification in the periphery compared to the center?
distortion
Distortion:
magnification (inc/dec) at periphery for plus lenses?
magnification (inc/dec) at periphery for minus lenses?
increases
decreases
_ and _ are minimized by the pupil
spherical aberrations
coma
_ and _ may be minimized individually by selecting appropriate base curve
radial astigmatism
curvature of field
if RA is eliminated, then effects of curvature of field will _ (and vice versa)
be enhanced
_ cannot be eliminated
distortion - not very problematic
What are the 2 most important aberrations to control?
Radial astigmatism
curvature of field
The locus of far points for all possible viewing angles is called _
far point sphere (FPS)
the _ meridian contains the optical axis and the off-axis object
tangential
with horizontal focus of radial astigmatism, _ will appear clear
with vertical focus of radial astigmatism, _ will appear clear
vertical boundaries
horizontal boundaries
radial astigmatism is induced if lens are tilted:
pantoscopic tilt means:
faceform tilt means:
on horizontal axis - reading glasses
on vertical axis - sports lenses
for pantoscopic tilt, 1mm OC drop for every _ degrees of tilt
2
with curvature of field, the dioptric difference between the actual focal point and the desired focal point is called?
power error
the more off axis you get, the _ the deviation
greater
3 ways to construct a corrective curve lens:
point focal lens
percival form lens
minimum tangential error
corrective curve lens design: correct radial astigmatism and leave power error uncorrected
point focal lens
corrective curve lens design: minimize power error, but leave some residual RA
percival form lens
corrective curve lens design: partially corrects both errors (compromise)
minimum tangential error (most common)
What 4 parameters must you consider when constructing a lens? Which one is most important?
vertex distance, lens thickness, refractive index, front and back surface powers (most important)
Tscherning ellipses does not eliminate RA for _ or _
aphakes or high hyperopes (high + powers)
plano lenses generally have back surface curves of _
as lens become more minus, the back surface _ and front surface _
-6.00 D
steepens, flattens
as plus lens power increases, the back surface becomes more _, and the front surface becomes _
flatter, steeper
When 2 lenses call for different BC:
if both plus: choose _
if both minus: choose _
if one +, one -: choose _
steeper
flatter
higher numerical value (usually +)
