RE: UV photography

[Rolland Elliott <rolland_elliott@xxxxxxxxx>]

First of all many thanks to Andrew Davidhazy and Jason Revell for
responding to my UV questions.

Jason asked:
<As for the use of a UVtransmitting filter over the >flashes may I
enquire why? Thiswould surely only be needed if one was not in place
over thecamera lens.

Actually, if I understand the theory correctly UV tranmitting filters
are needed over the flash heads for UV fluorescence photography to
prevent visible light from hitting the subject.  
In practice I think one would set a high shutter speed so that the
ambient(visible) light exposure would be negligle compared to the
flash exposure which is just emitting UV light.  This UV light then
hits the subject and is absorbed, reflected and fluoresed (transformed
to visible light).  A UV blocking filter on the camera then allows the
fluorescence to be recorded while blocking UV light from reaching the
film.  
The resulting picture therefore only records the fluorescence  of the
subject. No UV light or reflected ambient light that is not due to
fluorescence is recorded on the film.

I wrote:
>I have a feeling that B&W reflective UV photography >looks very
similar to "normal" visible light B&W >photography. Most B&W IR images
are drastically different than a normal B&W images, is the same true
for most B&W UV images. 

To which Andy responded:
>This is typically the case ... unless you happen to >find a subject
whose UVreflectance is different than its light reflectance! Same as
in IR. IR does not necessarily look different than visible ... it is
that we tend topoint ourcameras at subjects whose IR reflectance
characteristics differ widely from their visible reflectances. 

O.K.  So what kinds of subject matter have a UVreflectance that is
different than its visible  light reflectance?  
Another thing about IR photography is that it tends to be quite
contrasty due to the nature of the film and IR light.  I'm assuming
that the exact opposite is true of UV reflective photography. 
Subjects then to lack contrast and are hazy. Is this correct? If so is
pushing your film a good way to beef up contrast and at the same time
gain film speed? Thanks again.

Peace Rolland





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