From: Joachim Oppenheimer (joachim@microdsi.net)
Date: 06/04/02-03:46:36 PM Z
I appreciate your comments, but if you will check Kodak's Technical
publication (F-32?) on TMax films, you will note that in a table entitled
"Adjustments for Long and Short Exposures" (limiting my discussion to the
long end): At 10 seconds exposure Kodak recommends 1/2 stop increase for
both 100 ASA and 400 ASA (the films are, of course, 2 stops apart in
manufacture). According to the table, that is a 15 second (instead of 10
second) exposure for both films. At 100 seconds, however, Kodak recommends
increasing the 100TMax by 1 stop and the 400TMax by 1` 1/2 stops. Kodak
rates the exposures as 200 seconds and 300 seconds respectively. (Obviously
exposure of these durations are limited to night photography and pinhole
exposures and do not live in the world of the Zone System). Kodak does not
extend its table beyond 100 seconds but it is evident from this that the gap
between ASA 100 and ASA 400 narrows significantly and at exposures beyond
this point disappears entirely and, in my testing for extended pinhole
exposures, the TMax 100 is actually "faster" than the 400. It has long been
appreciated that differences among films, their chemistry and manufacture,
impart certain individual characteristic that may, at time, run counter to
the conventional wisdom. Joachim
> -----Original Message-----
> From: Mike Finley [mailto:mike@efikim.compulink.co.uk]
> Sent: Tuesday, June 04, 2002 3:23 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: RE: long exposures, reciprocity failure and development times
>
>
> This seems highly unlikely. If true, zone system development
> wouldn't work,
> and I'm sure someone would have noticed.
>
> -----Original Message-----
> From: Joachim Oppenheimer [mailto:joachim@microdsi.net]
> Sent: 04 June 2002 18:25
> To: alt-photo-process-l@skyway.usask.ca
> Subject: RE: long exposures, reciprocity failure and development times
>
>
> As a sometimes-pinhole photographer I am aware that films differ in their
> response to reciprocity failure at least at the lower part of the
> curve. It
> is paradoxical that conventionally "Slower" TMAX-100 is "Faster" than
> TMAX400, if one looks at Kodak's data sheets. Underdevelopment removes
> silver halide uniformly from a piece of film so that a fixed percentage
> removal, say 10%, will have little noticeable effect in an area of silver
> halide deposition that is loaded with the silver salt but a
> proportionately
> greater effect in the thinner areas - 10% of an arbitrary one picogram
> silver halide leaves 0.9 picogram but 10% of 100 picograms still
> leaves 90.0
> picograms. I think the guide directing you in the opposite direction is
> incorrect. Joachim
>
>
>
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