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Subject: [M]: [M] f6.3 focal reducer, vignetting, digital correction?
From: Nigel Puttick
Reply To: mapug@shore.net
Date: Tue Jan 20 12:27:56 1998
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Dear all,
Just a thought...
It seems to be accepted that the f6.3 focal reducer inevitably causes
vignetting, or "porthole effect" on 35mm, to a greater or lesser extent
depending in part on exposure and composition. Has anyone tried correcting
for this digitally? If you took a "flat field" exposure on emulsion, then
digitised both the image and the "flat" in a 35mm scanner, you could
perhaps subtract one form the other and correct for the drop off in
brightness. Alternatively it may be possible to measure the drop off and
create a graduated circular "image" to do the same job.
Any comments?
Regards
Nigel
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