110
DISPLAYING THE MEASUREMENT RESULT
REFERENCE
• PSF (Point Spread Function)
PSF is defined as the power distribution of a point image, and in this simulation it shows a
focused image of light on the retina. Ideally, the image is focused on one point, but actu
-
ally due to aberrations in the optical system of the eye, including diffraction, it is not
focused on one point and observed with extension, even using an ideal lens. The Strehl
ratio is defined as the ratio of the central power of the ideal lens and the central power of
the working PSF. Therefore, optically the Strehl ratio is the best when it is 1.0.
• MTF (Modulation Transfer Function)
MTF shows the characteristics of the space frequency of an optical system, and in calcu-
lation it can be obtained with the Fourier conversion of PSF. An MTF image has black and
white stripes in a certain direction and is used to determine the degree of scale reduction
by which the stripes are still clearly visible.
Accordingly, it can be observed well when the space frequency is low and the contrast is
clear and becomes less observable as the space frequency rises. Normally, as shown on
the left, the space frequency characteristics of only X and Y directions are drawn, but here
it is displayed for all of the 180-degree directions. So, origin-symmetrically same values
are displayed.
• Simulations (Landolt Simulations)
As a way of simulating the retinal image viewed by the eye, there is a method to see how
the image looks on the retina, and the simulation can be considered as convolution inte
-
gration of the power (PSF) of the point image and the viewed image. Here convolution
integration of the PSF on the retina and Landolt's rings with the supposed size on the ret
-
ina is done. As the image is focused reversely with regard to top/bottom and right/left
when viewed by the eye, the simulation display shows extension by PSF symmetrically
with regard to top/bottom and right/left.
30 60 90 120
Space frequency [cycles/degree]
1.00
0.80
0.60
0.40
0.20
0.00
Contrast
: X
: Ideal
: Y
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