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

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

Some more ponderings and details:

On 30 Sep 96 at 0:03, Willem-Jan Markerink wrote:

> 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. 

Wrong again: he does mention electronic flash briefly, which
apparently has a rather good output continuously down to 300nm,
provided it doesn't have an UV block filter built in....
No exposure data given....:-((
You can get a tele contraption for the Metz 45 and 60 flashes, which 
would be nice for shooting wild life outdoors. One could even use an 
entire battery of those flashes....
You only need to think of what to do with the fried bird....8-))


> FWIW: daylight only extends to 300nm, at high altitudes 290nm. Below 
> 315nm is the level at which sun burns occur.

Forgot to mention: Guenter Spitzing was very fond of a Philips HPW
125 W high pressure mercury vapor lamp, peaking at 366nm
(2.7 W/10 nm, if that says anything for the experts). His reasons:

- high output
- cheap
- UV short pass filter built in (black light)
- not to far UV to be problematic for lenses (at 366nm, 90% is still 
transmitted by most lenses)
- safe for the human eye

Btw, on a side note: the fact that one doesn't see clearly when 
looking directly in those high output lamps is because the human eye 
fluoresces....:-))
  
> > 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!

I knew I read about an argument in favor of Ektachrome IR: 
This film lacks a yellow absorbing filter below the blue recording 
layer, so that all three color recording layers record UV, and not 
only the blue layer, as with most other color films. This results in 
better recognition of UV differences, like IR differences are also better 
recorded on Ektachrome than on HIE b&w.

Another bold statement: all films, color, b&w and IR are UV sensitive 
down to 235nm. 



> 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.

What you could also try is one of those IR-block filters sold 
separately in almost any video shop. You probably have to search for the 
larger sizes, since camcorders seldomly exceed 58mm.
The B+W number is #489, with a transmission of:
0%@xxxxx
50%@xxxxx, 
90%@xxxxx
|
90%@xxxxx
50%@xxxxx
0%@xxxxx

> > 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 
> search on the Net with Yahoo or Altavista, with the keyword UV.

Again forgot to mention something: try the newsgroup sci.optics. Very 
high quality answers, way more than the photo groups could ever 
provide. 

--
Bye,

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      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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Topic No. 12