Optics: Monochromatic Aberrations Flashcards
(40 cards)
When does a plane wavefront become a spherical wavefront?
After passing through a spherical lens
Where is the image formed if light is coming from infinity?
At the focal length of the lens
What causes a plane wavefront to become aberrated after passing through a spherical lens?
Optical aberrations
How are optical aberrations measured?
-an aberrated wavefront on the pupil plane
OR
-a point spread image at the image plane
Significant optical aberrations in the human eye:
-defocus
-astigmatism
-spherical aberration
-coma
-distortion
-field curvature
Aberrations degrade the…
Quality of an image
Aberrations are important in:
-the design of spectacles, contact lens, IOLs, and refractive surgeries
-correction of refractive errors
The ligth rays that strike the periphery of the lens are focused ___________ the lens than those striking near the lens center
Focused closer to the lens
Positive Longitudinal spherical aberration
When the marginal ray focus closer than the paraxial ray
Negative longitudinal spherical aberration
When the marginal rays are focused further away than the paraxial rays
The longitudinal spherical aberration can be affected by…
Different shaped lenses
The amount fo longitudinal spherical aberration is dependent on __________________________ as well as some other factors
The radii of curvatures of the front and back surfaces of a lens
When is longitudinal spherical aberration minimized?
When using Plano-convex shaped lens where the front surface is more convex
What type of aberration does the unaccommodated eye manifest?
Positive spherical aberration that increases with age
What happens to the amount of spherical aberration as the eye accommodates?
The amount positive spherical aberration decreases
What is night myopia?
Myopia that is only present under low illumination conditions
What to do for a patient that has night myopia?
Prescribe lenses that are slightly more minus power for pts that drive at night a lot
What is coma?
Spherical aberration off-axis
Why do both spherical aberration and coma occur?
Because the refractive power of a spherical surface is NOT uniform
When does coma occur?
When the light rays are oblique with respect to the optical axis
When is the coma positive? Negative?
When tip of comet pointed toward the optical axis = positive, pointed away = negative
Can coma occur with on-axis objects?
Yes, when the optical components are non-centered and tilted with respect to each other
Coma can be a major foveal aberration in a ___________ eye
Decentered eye
How to reduce coma?
Place the aperture closer to a lens and decrease the diameter of the aperture
