Ocular Image Quality, Ocular Aberrations Flashcards
At what pupil size do we have the best overall image quality?
2-3 mm
What happens to high order aberration as pupil size decreases?
As pupi size decreases, high order aberrations increases
What occurs in geometric blur when the image of a point object does not fall on the retina?
Image will be blurry
What happens to geometric blur of myopes, hyperopes and emmetropes as pupil size increases?
For myopes and hyperopes the image get more blurry by the same degree in each
Emmetropes have no effect b/c the image is focused on the retina
How do we calculates the geometric blur size?
𝑏𝑙𝑢𝑟 𝑚𝑟𝑎𝑑 = 𝐷 ∗𝑝𝑢𝑝𝑖𝑙𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑚𝑚
𝑏𝑙𝑢𝑟 𝑎𝑟𝑐𝑚𝑖𝑛 = 3.44∗𝐷 ∗𝑝𝑢𝑝𝑖𝑙𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑚𝑚
What happens to blur when we increase defocus?
What happens to blur when we increase pupil size?
Blur increases
What occurs to the images during blur due to diffraction?
The image of the point is no longer a point, will have more spread
EX: iris produces a disk surrounded by faint rings
How does diffraction affect the image quality in optical systems? What factor are considered for the image produced by diffraction?
Limits the image quality
Generally unavoidable
The bending of light around corners when wavefront is interrupted by barrier or obstacle
Image is a result of: aperture size, wavelength and interference
What is an airy disc? What kind of diffraction is it produced by?
Airy disk is a point spread function for a perfect optical system
Produced byFraunhofer diffraction of the light by the circular aperture (pupil)
Depends on size of aperture and wavelength
Describe the distribution of total light intensity in an airy disc.
84$ of total light intensity in the central disk
16% distributed in the concentric rings
For blur size due to diffraction, what occurs to blur as pippin size increases? As wavelength increases?
If we INCREASE Pupil Size, we DECREASE Blur
If we INCREASE Wavelength, we INCREASE Blur
How does the size of the diffraction pattern compare to the aperture diameter? Wavelength?
The size of the diffraction pattern (θ) is inversely proportional to the aperture diameter (d).
The size of the diffraction pattern (θ) is proportional to the wavelength (𝝀).
Bottom line: the larger an aperture and/or shorter the wavelength, the less the impact of diffraction on reducing image quality
What happens to the airy disc as the pupil size gets larger?
Airy disc gets smaller
Describe the resolution of multiple point sources? What is the limit of resolution?
Each point source produces an Airy disc in the image plane.
When the sources get close together, the Airy
disc patterns overlap until they can no longer
be resolved as distinct objects.
The smallest value of the angle for which
images of two points can be detected as two
distinct objects is the limit of resolution.
Describe the resolution of multiple point source
9unresolved, Rayleigh and Resolved).
Unresolved shows as one point
Rayleigh is the point where 2 points can first be identified
Resolved is two separated points
