Final Flashcards
What are the causes of aberrations?
- the way light is refracted by a particular surface
- index of the medium
- location of the object point
What are the two types of aberrations (and what is each dependent on)?
- chromatic aberrations (lens material)
2. monochromatic aberrations (lens form design)
What chromatic aberration occurs in lenses that have a vergence effect? 1. What is the test that uses these aberrations? 2
- longitudinal chromatic aberration
2. Duochrome (red/green) test
What is used to control chromatic aberrations?
a doublet
What is the aberration that results from differences in the prismatic effects (angular dispersion) of the lens for the various wavelengths?
transverse chromatic aberration
What, in theory, would eliminate chromatic aberrations?
one wavelength (monochromatic)
What two factors in lenses are related to more dispersion and therefore more chromatic aberrations?
- high index lenses
2. low Abbe value
What are the five monochromatic Seidel aberrations?
- spherical
- coma
- oblique astigmatism
- curvature of field
- distortion
What causes spherical aberrations? 1. What does it affect? 2
- different zones of the aperture have different focal lengths
- sharpness of image point
What type of optical system is spherical aberrations usually involved with? 1. What is the path of the light rays that are impacted? 2. Is it usually ignored or addressed? 3. When is it a problem (and what is done to fix it)? 4
- large aperture
- parallel to optic axis
- ignored
- high plus lenses (aspheric lenses)
What causes coma? 1 What does it affect? 2
- oblique rays refracted by a large aperture optical system
2. sharpness of image points
What type of optical system is coma aberrations usually involved with? 1. What is the path of the light rays that are impacted? 2. Is it usually ignored or addressed? 3.
- large aperture
- oblique to optic axis
- ignored
Which is more significant: coma or spherical aberrations?
spherical
What causes oblique astigmatism?
narrow pencil of light passes obliquely through a spherical surface and form interval of sturm with 2 line foci and circle of least confusion
What are the two line images formed in oblique astigmatism (and which is steeper)?
- tangential focus (steeper)
2. sagittal focus
What equation provides the mathematical solution to eliminate oblique astigmatism?
Jalie’s equation
What are the two possible lens designs using Jalie’s equation (and what is the distinguishing factor in each)?
- Wollaston (steep base curves)
2. Ostwalt (flatter base curves)
Is oblique astigmatism usually ignored or addressed? 1. How is it addressed? 2
- most significant aberration so not ignored
2. lens form (base curve)
What is the benefit of Wollaston form lenses? 1. What is the benefit of Ostwalt? 2
- also minimizes distortion
2. more cosmetically appealing
What must be sacrificed to address oblique astigmatism?
curvature of image distorted
What is the aberration where the lens does not form a plane image for a plane object? 1. What is this image known as? 2
- curvature of image
2. Petzval’s image
Is curvature of image usually ignored or addressed? 1. How is it addressed? 2
- second most significant aberration so not ignored
2. lens form (base curve)
When is there no curvature of image aberration?
when far-point sphere coincides with Petzval surface
Why does distortion occur? 1. What does it affect? 2
- variable magnification across lens
2. shape of object