> models leading to lots of sales of "hot filters". It is hard
> to draw
> the line since people who regulary do IR photography have
> complained
> loudly when all the IR spectrum is filtered out. It could be
> that the
> 20D sensor filter is more carefully designed than the one in
> the A1
> and the light you are seeing in the image is not visible to
> the eye.
> Your polarizing filter may have a well designed cutoff in the
> non
> visible spectrum, especially if it is a multicoated one.
Ok, let's think about this. The strobes were pretty much the
exclusive light source for the paintings. As such, you have a
known spectral characteristic of the light source. If the A1
and the 20D were to respond to this light source differently, it
would be evident for any flash exposure. And I know that my A1
and E-1 use exactly the same exposures (A1 adjusted for the 2/3
stop ISO error).
If the paintings were protected with a UV reflecting coating (or
reflective glass) the spectral characteristics of the two
sensors would be a possible explanation. One way to test this
is with a UV light source in a darkened room and using identical
exposures with the cameras. If the A1 is more sensitive to UV,
you would see a greater brightness level than with the 20D.
I still think it was just an A1 oddity, but maybe worth
pursuing.
AG
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