Re: 18A UV pass filter for studio strobe lights

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

On 15 Apr 99 at 10:05, Rolland Elliott wrote:

> I'm going to use these filters over a Quantum X2
> strobe, and two Lumedyne portable strobes I have for
> UV photography. With a little black electrical tape
> these filters fit perfectly over the strobe
> reflectors. Since many strobe reflectors have about a
> 5 inch diameter opening they could probably be taped
> on to a wide variety of strobes.  The filters are
> domed shaped and made of thick glass (about 8mm
> thick!)  so they probably wouldn't be good for
> mounting over a  camera lens.  They might also be good
> as a filter for IR surveliance photography since there
> is only a dim purpleish red glow from them when the
> strobe fires.  Sorry don't know the specific
> wavelengths they pass.

Initially I wondered what the origin of these dome-shaped filters
could be, but then it dawned on me: UV-detecting or UV-curing
lights, probably with a special high-intensity UV/Quarz bulb. In
most automotive aircoshops you can find such a device (used to
detect leaks by first adding an UV-fluorescent fluid to the gas). 

> 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.  

I am afraid you are confusing UV-fluorescent photography with 
UV-reflective photography....
(UVFP and UVRP from now on....:-))

UVFP means recording patterns on film which are normally visible to
the human eye, but which patterns are triggered by UV-light, as
those fluorescing effects are mostly in the visible range (there are
a few outside the visible, in both UV and IR I believe).
This is what will give you a wide range of colors.

UVRP means recording patterns on film which are invisible to the
human eye, and this requires an UV-sensitive film....but *because*
you are recording UV-only in this case, all you can expect is a
monochromatic image (b&w or color)....unless you can find a film
that has more than one layer of (final) color, sensitive to small
differences in UV (say 360-380nm creates blue, 380-400 creates
green, and 400-420nm creates red)....but AFAIK, such films don't
exist, it's all monochromatic in this range.... 

> 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. 

Mmm....not sure how effective the IR-blocker is....have you tried 
without? Any difference?
Might also vary a bit with the time of day.
 
> I few weeks ago I posted that I would be trying to use
> old EL Nikkor enlarging lenses for UV photograhy since
> Nikon claims they are corrected for UV light down to
> 350nm.  I just ordered an old Nikon III bellows and a
> Nikon adapter that goes from Nikon's F-mount to a 39mm
> thread (nikon makes this adapter). This will allow me
> to easily mount and focus the enlarging lenses on my
> Nikon camera. I'll also have to order a B+W 39mm 403
> UV filter since handholding a larger filter infront of
> a lens doesn't work when the exposures are more than a
> second.

Can't you rig up some tripod-extension contraption, using the bellows 
tripod socket? 
For example a flat metal bar protruding from under the bellows to the 
front, with a short 90 degree angle on the end, to which you could 
tape the filter. Perhaps not a permanent solution, but at least good 
for some experiments, without increasing filter cost.
 
> 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.

Personally I would rather hold out for a Zeiss 350/5.6 Super 
Achromat....;-)) 
(the older 250/5.6 Super Achromat can be found used for US$3-4k)
Add a Hassy 70mm back and both IR and UV photography will get close 
to perfection (don't think these lenses were ever available for Rollei 
66/600x....Rollei also has a 70mm back available for the 600x).


--                 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
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