From:             "Jason Revell (in5)" 
To:               "'IR-List (postings)'" 
Subject:          RE: UV Fluorescence Photography
Date sent:        Mon, 7 Jun 1999 09:34:00 +0100 
Send reply to:    infrared@a1.nl

> I was wondering if anyone on these lists has much
> experience with UV fluorescence photography.  I have
> at my disposal about 20 UV fluorescent light tubes
> (black lights), that are 15 watts each for a total of
> 300 watts of UV light.  Although this sounds like a
> lot of light, it actually is fairly dim, unless the
> object fluoresces.  How should I meter a subject lit
> by UV light?  I don't think a gray card will work
> because it looks very dark under UV light.  Also what
> kind of films would one recommend?
>
> Any help insight would be appreaciated.
>
> Thanks Rolland Elliott


Rolland,

What sort of UV (black lights) are they?  Their are two basic sort's; BL and
BLB.

BL are the unfiltered ones often used for Alt. Printing and give off what
appears to be a blue/white light and look white when not switched on.
BLB are filtered, are usually the ones used in pubs and theatre for UV
effects.  These give off  blue/purple light when on and look a dark blue due to
the filters when not switched on.

These bulbs both give off the wavelengths of light you need to the
fluorescence but the BL give off  visible light as well.  So if you are
wanting a dark/black background or just the fluorescence to show use the
BLBs.

Metering for the fluorescence will be your problem, we can only see it when the
lights are turned down in a room so it is very dark in terms of photographic
light.  I use a exposure of 1 min at f5.6 when photographing the works of art
here (using 100 asa film).  This is when they are light by 4 x 4ft BLB tubes in
reflective housings at about 1.4 meters.  I think you might find you are using
slightly more light and your fluorescence will be brighter than mould and
varnish.  On this basis I would suggest that you bracket from about 1/4 to 30
secs at f5.6 or equivalent exposures, this is about the only way.

Film to use would be ANY.  Your fluorescence is 'visible' light so all film will
record it.  I would however say you are better using daylight film rather than
tungsten.  Also if your tubes are the BLB's ( and to a lesser extent BLs) you
will find you get quite a lot of UV light in the background showing a blue as
films are still sensitive to UV light.  To avoid this you will need to place a
yellow or near yellow ( I use a wratten 2E) over then lens to block out the UV
light the film is sensitive to, so only the fluorescence is recorded.   A normal
UV(0) filter does not block long enough wavelengths to have any effect with this
blue 'fogging'.

Also, just one last thing.  Remember that UV light is harmful to your eye's, so
don't stare into your light bank and some form of eye protection (sun-glasses
for example) would be strongly recommended.

I hope this helps you, and let me know if you have any further questions.

Jason
jason.revell@unn.ac.uk
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