Re: 18A UV pass filter for studio strobe lights

[Andrew Davidhazy <ANDPPH@xxxxxxxxxxxxxxxxxx>]

> With any luck I'll be able to get shorter exposure
> times using strobes.  For my first try with UV
> photograhy I used a B+W 403 UV pass filter with
> several lenses (a Nikkor 300mm f/4, 20-35 f/2.8
> Tokina, & 70-210 f/2.8 Sigma) along with Fuji RTP
> Tungsten 64ISO film.   My intial results were
> horrible.  Most of the pictures didn't even turn out.
> The few that did had exposure times of two to eight
> minutes at f/11. (in bright midday sunlight)  And
> these images were  only one color, a navy blue.  Seems
> like I could have gotten similar images by using a
> deep blue filter over any camera lens.

This is to be expected. The UV filter blocks all visible but allows UV to pass.
This exposes the top layer on your film. Since you do not have green or red
passing through the filter obviously you will not get any colors other than
blue. 

> For my second attempt I used the same lenses and Kodak
> Color IR film rated at ISO200. This time I used the
> B+W 403 UV pass filter and a blue/green IR blocking
> filter made by B+W.  The resulting images were awful.
> It appears that the blue/green IR blocking filter
> doesn't do a very good job since most of my images
> were totally red with some purple highlights.

Again, this is exactly as things are supposed to turn out ... although either
the blue/green filter is not very good or the UV filter passes wavelengths that
the blue/green filter also transmits. Logic goes like this. The blue/green
filter does not absorb all IR wavelentgths. The UV filter has a significant
red and IR transmittance. You film is sensitive to IR, red and green. There is
little green or maybe even little red passing through. The top layer is IR
sensitve and controls the cyan layer. The more it gets exposed the less cyan
and thus the more red the subject appears. This indictes that wherever exposure
takes place there is lots of IR and this will look red!

> Hopefully I'll figgure a way to take great UV pictures
> without spending $3,000 dollars on Nikon's UV 105
> f/4.5 lens.

For spectacular results I would concentrate on UV excited fluorescence
photographs. This you can do on regular color film. For spectacular color IR
photography you need only a deep yellow filter over the camera lens to remove
the blue to which all three layers are sensitive.
                                                                   
regards,

Andy  o o  0 0 o . o  Andrew Davidhazy, Imaging and Photo Tech
       \/\/\/\/\/\/   http://www.rit.edu/~andpph  716-475-2592  
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