Calculate cos4th offaxis fall off data
optics = cos4th(optics,opticalImage)
The irradiance of a uniform radiance input field declines as
we move from the principal axis to off-axis locations. This is called
the relative illumination, or sometimes the cos4th fall off. This
formula applies as a good approximation in many cases. More detailed
calculations for specific lenses can be obtained using ray trace methods.
The algorithm handles the case of a distant image separately
from that of a close image.
Formula:
d = distance from the lens to the image plane
s = sqrt(d^2 + fieldHeight^2)
fN = f-number
If d > 10*image diagonal size
RI = (d / sFactor).^4;
else
m = magnification
A complicated formula
Example:
Copyright ImagEval Consultants, LLC, 2003.
Setting up local variables