Re: [APML] Speeding up film with cold weather

["John C. Mirtle" <jmirtle@shaw.ca>]

From: "Alan Voetsch" <critter12952@yahoo.com>
To: <astro-photo@seds.org>
I'll quote from the book by Jack Newton and Terance
Dickinson, page 108.

"For every drop of 20 Celsius degrees (35 Fahrenheit
degrees) most films gain about one f-stop; that is, a
400 speed film acts like 800 speed film around 0
degrees C (32 degrees F) and like 1600 speed film at
minus 20 degrees (-4F), and the process keeps going.
<- snip ->

Alan;
    This is a bit misleading. Film doesn't gain any speed by chilling it, it
is still 400ASA or whatever. What chilling CAN do is reduce reciprocity
failure by slowing down the decay rate of the latent image during the
exposure. (as I understand it) It produces the same end result as gas
hypering, but without the storage/humidity issues and without introducing a
base fog level. As either chilling or gas hypering can (almost) eliminate
reciprocity on their own, combining the two techniques does not produce an
additive effect.
    The main difference between the two techniques is where you do your
fiddling. Hypering film involves fiddling around in the darkroom, cold
cameras involve fiddling around at the telescope. As there is a current
shortage of negative films that work well hypered or untreated, it might be
worth my while to dust off the cold camera again. I have some slides I use
at presentations that shows how dramatic the effect of chilling is. If I
have a few minutes, I will scan them up so that you can decide for yourself
whether or not the effect is real or imagined.  Who knows - with Peltier
coolers potentially replacing dry ice, perhaps this "dead parrot" isn't just
nailed to it's perch afterall... :-)
    Famous astrophotographers of the past with frostbite burns include Jack
Newton, Evered Kreimer, Orien Ernest, Leo Henzl and Ben Mayer.(sp)

John (cold hand) Mirtle
Calgary, Ab. Canada


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