Re: Nighttime and astrophotography with IR

[joneil@xxxxxxxxxxxxxxxx (Joseph O'Neil)]

tom@xxxxxxxxxxxxxxxxxxxxxx (Tom Benedict) writes:
> 
> An alternative you might look into is straight vacuum treatment (no
> hypering gasses or baking, 'far as I know).  The speed increase isn't
> as marked as with hypering, but you can see improvement on Tech Pan.
> Once again, there's a section in Michael Covington's book about vacuum
> treatment, so he'd be a better reference than I would.
-snip-
      Michael can be found on the astro-photography mailing list.

Astro-photo@xxxxxxxxxxxx   I beleive you write to majordomo@xxxxxxxxxxxx 
with the mesage "subscribe astro-photo"

  I do some hypering of tech pan myself.  Most hypering is done at 30 to 
50C, which I beleive would spoil most IR film.

   Two things happen when you hyper a film.  First, the heating and the 
vacumn combine to remove water and oxygen formt he film emulsion.   This 
helps retard reciprocity failure.

  The second is hydrogen in the forming gas used combines witht he silver 
crystals in the film emulsion, and raised the effective ASA/ISO of the 
film

  Colour films only increase in speed by 2-3 times, but hypered tech pan 
often has an effectiv4e speed of 1000 ISO.

  drawbacks are that the benefits of the hypering are short lived.  In 
other words, use up the film right away, and develop right away.  teh 
exception is tech pan whihc, in a dry climate, seems to retain it's 
positive effects for a week, and up to 6 minths frozen.

    Why tech pan is so desireable for astro-photography, and the interest 
in other IR or red sensitive films, is the the wavelenght of light from 
Nebula goes drpp into the red, even the IR.

  Most Black and White films have terrible red responsiveness.  Not all 
colour films are that great either - at least not to the range 
astro-photographers are looking for.

  This is one reason I am so interested in testing out the new Ilford 
film.  It may be just perfect for astro-photographs.   Very red 
sensitive, but perhaps not IR sensitive enough to be runied by hypering.

   It should be possible to hyper IR films at room temperature.  It would 
take longer (perhaps a wek in forming gas),a nd you would need a very 
good vacumn.  I use a hand pump,a nd can only get down to -26.  For IR 
and low temp, you would need a mechanical pump that would take you down 
to a vacumn measured in microns.

   There have been several tests to show that film hypering done in a 
near perfect vacmun is not only faster, but sometimes more effective.  
The drawback is a good mechanical vacumn pump is usually expensive.

Good luck.
joe

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Topic No. 8