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Path: utzoo!decvax!genrad!panda!teddy!rdp
From: rdp@teddy.UUCP
Newsgroups: net.rec.photo
Subject: Re: Pushing high-speed film
Message-ID: <1769@teddy.UUCP>
Date: Fri, 6-Dec-85 09:50:24 EST
Article-I.D.: teddy.1769
Posted: Fri Dec  6 09:50:24 1985
Date-Received: Sat, 7-Dec-85 02:31:18 EST
References: <259@watmath.UUCP> <788@sfmag.UUCP> <318@polaris.UUCP>
Reply-To: rdp@teddy.UUCP (Richard D. Pierce)
Distribution: na
Organization: GenRad, Inc., Concord, Mass.
Lines: 18
Summary: 

In article <318@polaris.UUCP> herbie@polaris.UUCP (Herb Chong) writes:
>
>>* I have heard that in the magazine ASTRONOMY, there are articles on using 
>>  chemicals (nitrogen?) on film before it is used to take shots of celestial
>>  nature at "very" high speeds. 
>
>mercury vapor and acetic acid are well known (and dangerous) ways of
>doing it.  very cold (like -150 C) film is also more sensitive.
>pre-flashing of film with a very short exposure to a white evenly lit
>surface will also provide about 1 stop of real speed increase.
>
There are several different things happening here, in fact. First, chilling
the emulsion duringh exposure DOES NOT increase it's base sensitivity at all,
it simply reduces or eliminates the reciprocity failure. Tri-x, with a 
supposed ASA of 400 still hass that sensitivity at very low light levels
when chilled, not more. Some gases (hydrogen) can truly increase sensitivity.

Dick Pierce