[Leica] Pre-Distortion and Vignetting: No corner vignetting

[red735i at earthlink.net (Frank Filippone)]

There are a number of applications where the distortion in a system is
either known or can be measured.  Telecommunications is probably the main
application area.  If you know the distortion in a system, you can pre
distort a signal and make it appear at the receiving end as a undistorted
signal.

Applying this to optics, and especially vignetting, it is easy enough to
predict or measure the light loss in a lens as you go from the center of the
lens' image circle to the periphery.  In LF terms, you then make a (very
expensive ) ND filter to compensate for the light loss on the periphery.
Typically these are called "center spot" ND filters.  They are made for
specific light losses of lenses.

Now moving this back to the arena of digital cameras, knowing the loss and
angle of view for each pixel location of a specific design of lens or
measuring it, you then apply an algorithm to each pixel location to
establish a flat transmission image plane through the electro-optical
system.  It actually is pretty easy.

Frank Filippone
red735i@earthlink.net