Cold film and exposure

["allan carrano" <allan.carrano@xxxxxxxxxxxxx>]

     "Richard M. Koolish" writes:
     
     >Astronomers use 'cold cameras' which use dry ice to cool the emulsion 
     >to prevent reciprocity failure, so maybe the emulsion actually speeds 
     >up.
     
     If there are any astronomers out there, I know they can clear this up 
     reasonably quickly.  I might be able to do so myself if I only had a 
     br..., I mean a better memory.
     
     About 10 or 15 years ago I read an article (somewhere) on how 
     astronomers reduced exposure times by pre-treating film to a non 
     oxygen atmosphere.  I don't recall whether inert gases were used, CO2 
     or Nitrogen.  
     
     I do remember experimenting a little at the time with a nitrogen 
     atmosphere and Kodachrome 25.  I recall the effort was to increase the 
     effective ISO rating of the K-25 without losing the fine (no) grain 
     images after exposure. Neat!  Cool!  But alas, I left it there and 
     pursued no further.
     
     So, my recollection is that it wasn't the cold that affected the 
     exposure index of the film but the elimination of oxygen at the 
     emulsion surface.  Oh yes, I remember the effect lasted many hours 
     (maybe even a day or two - that I don't remember).
     
     Allan


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