Physical and Optical Characteristics Flashcards
Image Vergence
V = U + P
= object vergence + power
Real Image
exiting light with a positive vergence
Virtual Image
exiting light with a negative vergence
Real Object
incident light with negative vergence
Virtual Object
incident light with positive vergence
Paraxial Approximation
incident rays are close to optical axis
yields point image for point objects
Optical Axis
where light passes through undeviated
line joining 2 centers of curvature of a lens
Axis of Rotation
perpendicular to muscle plane that eye moves around
Lens Effectivity
change in vergence of light
2 lenses have the same lense effectivity if…..
make a real or virtual image at the same point
Marginal Rays
rays on periphery, far from optical axis
Paraxial Rays
rays in close proximity to optical axis
Aperture Stop
limits amount of light passing into an optical system
Field Stop
limits size of object that can be imaged by system
Depth of Focus
interval surrounding retina where an eye sees an object in focus
Short focal length =
large depth of field
Depth of Field
interval surrounding fixation plane where an object can be in focus
Increase aperture size =
decreased depth of field and focus
Aberrations
create optical distortions in image plane
Monochromatic Aberrations
wavelength independent aberrations
spherical, coma, radial astigmatism, curvature of field, distortion
Chromatic Aberrations
longitudinal and transverse
Spherical Aberration
peripheral rays focus at different points on optical axis than paraxial rays
Longitudinal SA
length of blur circle
marginal and paraxial rays focused at 2 different places
Lateral SA
area size of blur circle
Increase in pupil size _____ image quality
decreases
more aberrations
Coma
comet shaped
from various magnification in height of incident rays
Aberrations cancelled by small pupil size
spherical aberration and coma
Necessary to compensate for spherical aberration
very high powered lenses
Influence effective power of a lens
vertex distance- increase- more minus; decrease- more plus
rays at oblique angle- makes astigmatism and spherical
Oblique Astigmatism
from rays hitting lens obliquely causing power to be altered
warped image plane
Difference between sagittal and tangential power
oblique astigmatism
Curvature of Field and Oblique Astigmatism
different warping along two principal axis
Petzval Surface
image surface created by a system with no OA
When is the curvature of field present?
when Petzval surface does not correspond to the far point of the eye
Corrected Curve Lenses
lenses corrected for OA, curvature of field, or both
Point Focal Lense
lens corrected completely for radial astigmatism
curvature of field uncorrected
Percival Form Lens
lens corrected completely for curvature of field
OA uncorrected
Distortion
straight line objects that do not pass through the optical axis- curved
Distortion is more of a problem in….
higher powered lenses
Aberrations causing the most concern
OA
Curvature of Field
Distortion
Higher refractive index = ________ lens
thinner
Longitudinal Chromatic Aberrations
different wavelengths are focused at different distances from lense
Transverse Chromatic Aberrations
different wavelengths are focused at different points in same focal plane
blue light deviates the most
Red-Green test is based on….
chromatic aberrations
Chromatic Dispersion
quantifies the amount of chromatic aberration in a lens
Effects of Transverse Chromatic Aberration
impacts peripheral viewing
prismatic effects for different wavelengths
greater impact at higher powers, but need a lot to cause issues
Minimizing Chromatic Aberrations
shorter vertex distance
monocular PDs
add sufficient panto
Abbe Number
Bigger is better
higher index of refraction = lower number
