FROM: Bjorn Rorslett 
SUBJECT: Re: UV Photography without going overboard?
DATE: 05 Aug 1996 06:36:11 -0500
ORGANIZATION: NIVA


True UV photography in color is entirely possible using appropriate film 
material and ordinary lenses. However, all multicoated modern lenses are 
not eligible because they suppress UV too much. Also most modern color 
films incorporate a UV-absorbing dye. 

I entered UV photography because being a botanist became fascinated by 
the UV patterns exhibited by flowers. Such patterns are detected by 
insects and serve to guide them towards the nectar and pollen. Using a 
UV-Nikkor 105mm f/4.5 lens these patterns could be recorded on 
transparency film. My tests indicate that Fuji RTP, a tungsten-balanced 
film, is the superior choice for this purpose. Shy away from Kodak films, 
they are next to useless for UV photography.

There is a need to use a "true" UV filmer, i.e. a filter that passes UV. 
Nikon provides a special-order item for the UV-Nikkor called FF filter. 
This is supplied with a holder device intended for 52 mm filter threads. 
This filter is quite similar to Wratten 18A and has a secondary 
transmission lobe starting at around 690 nm. In consequence, besides UV < 
400 nm some deep red can pass. Alternate choices for true UV filter are 
sold by Hoya (U-360) and Schott of Germany.

Exposure time for ordinary landscape scenes in bright sunlight is around 
f/8 at 1/15-1/30 sec for RTP film in conjunction with the FF filter and 
UV Nikkor 105mm. Remember that UV radiation is highly diffuse and gives 
very soft shadows. Extremely nice, dreamlike landscape images are 
possible using this setup. Another interesting and significant feature is 
that UV, being shortwave, gives extremely sharp images! RTP thus is much 
sharper than Velvia in this case...

Not everybody would be interested in paying the elevated asking proce for 
the UV Nikkor. Alternatives exist however. Old non-coated or 
single-coated lenses can function well. I have used a multitude of Zeiss, 
Leica, Canon and Nikkor lenses to this end. Such lenses tend towards 
quite soft images because they are not optically corrected for the UV 
area. Thus exposure times have to be increased.

The ultimate alternative is pinhole photography using Fuji RTP in 
rollfilm or sheets and placing a "true" UV filter in front. It is readily 
appreciated that using UV in this way gives much sharper images than 
otherwise thought possible in pinhole applications.

Try it for yourself. Getting the proper exposure is simple using the 
Nikon F4 with UV-Nikkor because the F4 meter in fact reads correctly. 
Haven't the slighest idea why, and neither the F3 nor the F5 behaves 
in a similar fashion. 

Regards
Bj. 


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