Judy Seigel (jseigel@panix.com)
Sun, 07 Mar 1999 16:19:46 -0500 (EST)
On Sun, 7 Mar 1999, Tom Ferguson wrote:
> What we are seeing here may be more than contrast change due to
> underexposure. I suspect that we are seeing reciprocity failure/effect.
> I've found that beyond 15 seconds, APH film changes contrast significantly
> with increased exposure time. 15 seconds at F8 is NOT the same as 1 minute
> at F16! I've settled on one "standard" time, and vary exposure by F-stop.
>
> If I remember correctly, the higher numbered variable contrast filters also
> have a higher filter factor?? It has been a long time since I used these!
> If so, the students may be using the higher contrast filters, and thus
> increase their exposure time, and thus get reciprocity failure, and thus
> get more contrast. If I'm correct, it would be a lot easier to simply stop
> the lens down ;-)
Tom, that's a remarkable possibility, although I doubt that it obtained in
the students' cases.... Times with the APH were extremely short -- onto
4x5 we were already at the borderline, f-16 for a second or two, in fact
used magenta filter for a "neutral density filter" since that is by law
also missing in photo dept's.
In all these years I don't think I myself ever exposed APH longer than 25
seconds.... but your system cries out for "exposure" so to speak. Can it
work somewhere else besides California? Wow !
Judy
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