RE: [APML] Scanning slides (Was IC 410 uploaded and IC 405 adjusted)

[John Mirtle <spampit@shaw.ca>]

Stuart,
	The nice thing about E200 is that it has almost no reciprocity
failure. Taking someone's f-ratio/exposure time and translating it to
another f-ratio gives a very close time for the same effective exposure. Few
films can boast this and with E200, my biggest problem is a tendency to
consistently overexpose the darn stuff. This is why I am so baffled by
Alan's results. The exposure times are way longer than most and yet don't
capture what I would expect. It's almost like there is a moon filter in the
optical path somewhere! It just doesn't make sense. Alan has a few new
things to try, hopefully things start to improve without having to expose
for 7 hours again...

John M.
Calgary, Ab. Canada

-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org] On
Behalf Of Stuart Heggie
Sent: Wednesday, November 03, 2004 4:08 AM
To: Discussion of Film Astrophotography
Subject: Re: [APML] Scanning slides (Was IC 410 uploaded and IC 405
adjusted)

Alan and John, I've been (sort of) following this dialogue. Something I
remember about film
emulsion that may be a factor is this: Each grain has to be hit by more than
a certain number of
photons or the chemical reaction reverses (so I'm told). This suggests that
at sufficiently high
f-ratio and hence exposure time, the number of photons hitting the grain in
the emulsion is too few
over any time frame to sustain the chemical reaction and so you are losing
signal. CCD is linear
and would not be affected but film would be.

Does that make sense? (and did I just repeat something you two said about 8
exchanges ago?)

Stuart


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