CN writes:
>>But I do agree that I think the circular polarizer is not
>>quite as effective. The only circular polarizer I have for digital
use
>>is a 72mm B+W Kaesemann which I bought on ebay from a Chinese seller
for
>>not very much less than I could have gotten it stateside. When I
first
>>got it I was concerned that (despite it's wonderful construction and
>>machining) it might be a fake since the polarization effect on sky
and
>>clouds wasn't as strong as I suspected.
Harumph, nary a listee read my post, not even Chuck this time. I
suppose that is reasonable given the dismal
senorita count.
The only real difference with the circular polarizer is the 1/4 wave
plate--typically designed for the middle of the
visible spectrum--though this does vary. The 1/4 wave plate will NOT
make perfectly circularly polarized light for all wavelenghs
so in a highly polarized sky there is a slight spectral shift to the
warm side--PERHAPS that is the perceived difference.
I have never seen a formal study of this though and it is a working
hypothesis. The polarizing foils used have different efficiencies at
various wavelengths as well but that is true for all the pols.
Chuck is spot on about the AA filters and possible interaction with
linear pols--birefrigent materials are used in the AA--one slab, then
1/4 wave retarder, then second slab so a square blur is formed.
A linear pol in front will screw up the front slab that would normally
result in parallel streams of light with horiz and vertcially
polarized steams---thus aliasing would occur on one axis. Suspect that
won't amount to a hill of beans unless the AA is strong and one has an
image in just the right pattern
and perhaps that would not even be noticable. Seems perfectly
reasonable to try and use them
Mike
--
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