Some "Conservation Glass" has UV coatings...
Bill Pearce
----- Original Message -----
From: "AG Schnozz" <agschnozz@xxxxxxxxx>
To: <olympus@xxxxxxxxxx>
Sent: Thursday, October 06, 2005 3:18 PM
Subject: [OM] Re: [OT] A very peculiar exposure problem
>> 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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