Flashcards in 9- Spatial Vision Deck (32):
What is spatial vision concerned with?
Variations in luminance across space
What are the 2 characteristics of sine-wave grating
Frequency and contrast
Low spatial frequency grating looks like
Bars more spread out
High spatial frequency bars look like
Lower contrast bars
High contrast bars appear
A lens is used to form an image of a sine wave grating. What does the spatial frequency depend on?
Magnification of the lens
A lens is used to form an image of a sine-wave grating. What affects modulation depth
The quality of the lens
For a real lens, as spatial frequencyof the object becomes greater, what happens to the amplitude?
What is resolution
An imaging systems ability to distinguish object detail
What is contrast
How faithfully the min and max intensity values are transferred from object to image plane
What does the MTF measure
The lens ability to transfer contrast at a articulate resolution from the object to image
As line spacing decreases what affect does that have on the lenses ability to transfer the contrast?
In an on axis optical system is there any change in phase with spatial frequency?
At low-moderate spatial frequencies do aberration have an affect?
Not as big as in high frequencies
What is the effect of optical defocus on SMTF?
Defocus results in a reduction in image quality at high frequencies
What is the effect of translucent optics on SMTF?
Overall reduction in overall reduction in image contrast at ALL frequencies
The image formed by the lens is highly degraded
For higher levels of defocus what happens to MTF
Decreases the then becomes negative
What happens to the image pattern with MTF is negative
What is the resolution limit
Spatial frequency at which the modulation transfer function first goes to 0
What is spurious resolution
Any resolution of higher frequency pattern
Point where the grating is first seen by the patient
What is the reciprocal of contrast threshold
What is the maximum sensitivity
What is the high frequency cut off
The point where the grating can no longer be resolved
What is the approximate high frequency cutoff?
How does the high frequency cut off relate to VA
It is the point where the details of the optotypes can no longer be resolved
What is the optical limitation of high frequencies
Manifests a high frequency limitation because of optical aberrations
What does the packing of retinal photoreceptor have to do with high frequency
A finer matrix is able to resolve better
What happens to high frequency cut off in uncorrected refractive errors
There is reduction in the high-frequency cutoff that manifests itself as decreases VA