Re: 18A UV pass filter for studio strobe lights

["Jason Revell (in5)" <jason.revell@xxxxxxxxx>]

>> I looked at the same web site, that was the one I remember and the film
is
>> indeed indicated in the quote above from the dandelion illustration. Now,
>> does anybody know what Fuji RTP film is?
>> Gary Beasley
>> http://beasleyglb.home.mindspring.com/

>RTP is professonal 64 T.

Well I have just come back from a weeks holiday and found this thread.  I
see most of the questions have now been answered but I do both UV
reflectance and UV Fluorescence photography so I can maybe through a bit
more light on the subject.

The photo's of the dandelion are indeed UV reflectance and the red colour is
due to the fact that the filter, Wratten 18A allows UV and IR to pass
through.  So with heavy IR reflectance you will record red/purple as well.
You will of course need a light source with both UV and IR presence, normal
flash (unfiltered) and tungsten lights are OK but not UV light tubes as
these give off no IR light.  The filter I use is actually the B+W 403 which
is the same as a 18A, and the best film is (from my experience) the Fuji
RTP, though I expect most tungsten balanced films would give the same
effect.  The reason for this is they all are much more sensitive to the
shorter wavelengths of light (blue) to compensate for their intended use
under redder light, this does of course limit the amount of far red that can
recorded but we never are able to get eveything are we?

UV fluorescence is the much more common type of photography, (we actually do
about 4 times as much of this as IR for the works of art) and it is also
much easier.  The subject needs to be lighted with just a UV source (BLB
tubes are the best for this) in a darkened room.  Then with a yellow filter
over the lens is used to block out all the reflected UV from the subject.
This allows fluorescence caused by the UV light to be the only thing
recorded onto the film.  As you are recording normal light any daylight film
can be used but longish exposures are required as the fluorescence can
sometimes be quite dim (unless you are using any 'fluorescence' colours in
which case you will need a more normal exposure time).  Any yellow filter
will do for this work, but most yellow filters will start to give a slight
colour cast which is of no use to us, so we use a 2E filter which cuts out
most of the reflected UV and has no effect on the colour of the
fluorescence.

I hope this is not going over dead ground, but if anyone has any further
questions please ask.

Jason
jason.revell@xxxxxxxxx
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