Re: 18A UV pass filter for studio strobe lights

["Michael J. Gudzinowicz" <m.j.gudzinowicz@xxxxxxxx>]

On Sat, 17 Apr 1999 16:08:44 -0400 (EDT) Andrew Davidhazy
<ANDPPH@xxxxxxxxxxxxxxxxxx> writes:
>> The photographer, Bjxrn Rxrslett, uses a Nikkor 105 mm
>> UV lens with a Nikkon 18A filter and gets three
>> distinct colors in his pictures: red,  blue and white
>> using reflective UV photography techniques.  If he can
>> do it, why can't I?
>
>I did take a look. It was interesting. Unfortunately he does not seem to
>explain how his photographs are made. This is especially important
because >they
>fly in the face of logic and physics and photographic principles. Poor
science.
>My contention still is that since the 18A filter does not allow any red
to pass
>you will not  see any red in an image. In fact, I think you will be hard
>pressed to see whites as well. But ... of course, he has the pictures to
prove
>it. What is lacking is a reasonable explanation.

The 18A begins to transmit "far red" at 690 nm, with a maximum near IR
transmission of 10% at 750 nm. The UV transmission spans 280 to 400 nm
with the maximum near UV transmission occuring at 360 nm. The filter will
leak red light if the intensity  is high on the red end. For true UV
photography, the 18A is usually used with a UV source (black light), so
the red leak isn't a problem (low intensity) and visible fluorescence is
blocked by the filter. 

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