Re: UV was Re: IR film & X-Rays ?

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

On 28 Sep 96 at 21:19, Zoe Paddy Johnson CIRT CSOS wrote:

> Geoff says:
> 1. I've heard that the wratten 18a is darn near opaque and that only 
> about 1% of a flash is UV, so that the exposures have to be really long, 
> like 2 to 15 minutes.  Is this right?

My IR-bible, 'Moderne Infrarot- und UV-Fotografie' by Guenter 
Spitzing, also has a nice part on UV stuff. I guess Geoff is right 
about flash, since neither this book nor the B+W books I have mention 
flash. Daylight, mercury vapor lamps, black lights, but no flash. 
FWIW: daylight only extends to 300nm, at high altitudes 290nm. Below 
315nm is the level at which sun burns occur.
 
> 2. What film would you recommend for taking UV photography?  I have been 
> thinking of Tmax P3200, pushed to something like 25,000.  Does this sound 
> reasonable?  What about a color film?

Both Kodak HIE and Ektachrome IR are known for their UV-sensitivity 
as well....they are even more sensitive to UV than for IR!
 
> 3  I have heard that the sun is the best UV source available so I have 
> been planning to take the pictures outside in the sun.  Does this sound 
> okay, or would another UV source be better?

It would at least be a cheap solution....:-))
 
> 4. I figure keeping a bird still for 2 to 15 minutes won't work, so I am 
> planning on starting on feathers.  Can anyone think of a way of 
> photographing a bird without blinding me and the bird in the process?
> 
> 5. I have heard the the glass in lenses and the metallic coats fluoresce 
> in UV.  Is this true?  A professor I have worked with at the university 
> thinks a special lens costing about $2,500 is needed.  Is this true?  To 
> get around this, I am think of using an old rollei TLR because there are 
> fewer lens elements and the coating seems thinner.  I have also thought 
> of using a pinhole camera (this is where the xray film would come in) 
> and exposing the stuff for about 8 hours.  I have also heard that 
> the fluoresence only happens in the far UV and I am interested in the 
> near UV because that is where birds see.  But I guess the film wouldn't 
> know that and would still get the UV in the far UV range, right?

You mentioned most of the specifics already: UV recording is
improved by lesser (non-kitted) elements and lesser coating (both
point at older and simpeler lenses). A strange other variable is
mentioned in Guenter Spitzings book, without further explanation:
tele lenses are better than wide angles....

What your professor at least forgets to mention are mirror
lenses....for both IR and UV photography the perfect solution. Since
you probably don't want to use super teles, you might want to check 
some older 250mm Minoltas. The Russians still produce a nice 300/5.6 
mirror with M42 screw mount. 
But I agree with Andy that your application is not very deep into the 
UV. Guenter Spitzing mentions the special lenses only for UV 
recording between 235 and 350nm. Below 235nm I think you need vacuum 
tanks, since air absorbs anything below that.
FWIW, besides the already mentioned UV Nikkor 4.5/105mm there are a 
few other exotics: 
Hasselblad Zeiss UV Sonnar 4.3/105mm
Rodenstock UV Rodagon 5.6/60 and 5.6/80, both enlarger lenses which 
can also be used for macro 
Zeiss UV Planar 2/50 and 4/60
Asahi Optical Industries (Pentax): several UV Ultra Achromatic Takumars

 
> 6. Anybody got feathers they want to send me?

If you have any kind of unique Dutch bird in mind, let me 
know....;-))
 
> 7. Anybody got a spare 18a to loan in the name of science <grin>?

Keep in mind that B+W also offers two UV short pass filters. The 
$200 Andy quoted in PhotoForum is rather offensive. I'll try to check the 
B+W price this week. The opaque one is #403, the deep-violet is #484.
As an exposure 'reference': the first requires a 8-20x longer 
exposure, the latter 10x.
One caviat to keep in mind with all filters: they block visible, but 
*NOT* IR! Most are IR transmissive, starting at 650 to 720nm. So to 
be absolutely sure you only record IR, you need a secondary filter, 
my book recommends a Schott 23. Not sure if the heat absorbing 
glass filters as used in slide projectors also block near-IR.
 
> 8. I will also take pictures of the same feathers in IR and visible 
> light, also.

Be sure to block the opposite end of the spectrum in both 
cases....easy with IR, not so with UV.
 
> 9. I have also thought about using a video camera since one like my 
> granpere's records down to .8 lumens.  Do camcorders record UV?  Do 
> CCD's?  If they do, how is it displayed (if it is recorded wouldn't it 
> help much if it only played it back as UV)?

I don't think they record much UV. I believe they are in the same 
league as image intensifiers, which also start at 400nm. Most 
camcorders have a IR-block filter build in, to clean the signal for 
light metering and AF. The same filter is found in SLR AF cameras 
btw, in front of the AF/AE unit, and responsible for the lousy IR 
sensitivity of modern cameras.
 
> 10. And now a question for my sister:  How deep does IR penetrate in 
> freshwater?  in saltwater?  How about UV in freshwater?  in saltwater?
> What about different colors of visible light?  (she is interested in fish 
> vision and when she asked her physics professor he said he didn't know 
> and wasn't sure where to look it up).

IR doesn't extend far in water, depending on wavelength. I believe 
the longer wavelengths don't even penetrate 1mm.
I guess a chemistry professor should know where to find numbers on 
both UV and IR penetration.
 
> I appreciate any help or suggestions, including "go look it up yourself", 
> if it includes some idea of a good place to start looking.
 
Seems as if you have found the Net sources already....you might try a