Physiological Optics 1.3 Flashcards
Longitudinal Spherical Aberration
Marginal rays focus in front of paraxial rays thereby blurring the image
- Occurs for both on and off axis points
- contributes to nocturnal myopia
- Increases with the square of the aperture size
Coma
Magnification varies for OFF axis points
- Gives a comet shaped patch
- Increases with the square of the aperture size
Lateral Spherical Aberration
Contributes to blur circle area
-Increases with the cube of the aperture size
How do you reduce Radial/Oblique Astigmatism
Pick the best base curve
Teacup and Saucer is associated with what aberration
Radial/oblique astigmatism
Tscherning Ellipse
Points showing the best BC to use to reduce radial astigmatism (and curvature of field)
- Ostwalt is the curve to use bc its flatter
- upper limit is around +7.50 and lower is around -22.00
Petzval Surface
Image surface created by a system with no radial astigmatism.
Curvature of field is still present unless the Petzval surface corresponds to the far point sphere of the eye
Image Jump Equation
(Seg drop) x (Add power)
Methods for Correcting Vertical Imbalance
Slab Off (applies Base UP to the more MINUS lens)
Dissimilar Segs
Compensated R Segs (only in glass lenses)
Contact Lenses
Fresnel Prism
Multiple Spectacles
Distortion (types and how to minimize)
Pincushion (plus lenses)
Barrel (minus lenses)
Minimize with orthoscopic doublet
-distortion does not cause blur
Longitudinal Chromatic Aberration
Variable image location, shorter wavelengths bend more
Inversely related to v (the Abbe number) [CA= F/v]
Lateral/Transverse Chromatic Aberration
Contributes to image size
-Inversely related to v (Abbe #) [CA = dF/v}
-Related to prismatic effect and becomes more harmful as prismatic effect increases
d = distance from optical center
How to eliminate chromatic aberration
Use an achromatic doublet (positive lens of one material and minus lens of another) so that CA1 + CA2 = 0 [F/v + F/v]
With lenses you can use a shorter vertex, mono PDs, and pantoscopic tilt
Aberrations of most concern
Oblique Astigmatism
Curvature of Field
Distortion
Deviation Angle/Apex angle Equation
Deviation Angle = Apex angle (n-1)
