From: Greg Schmitz (gws1@columbia.edu)
Date: 04/08/03-06:09:37 PM Z
Hi again:
I was almost tempted to say that this thread is off topic, but given
what the manufacturer's are doing to silver processes silver may soon
be a "post-factory" process and we will have to chase the digital
folks off to another list :*) (heheh - Hi Judy)
FWIW I have not used Plus-X for a while now but my recollection is that I
used to rate it somewhere around 32 (that's 2 stops off from what
Kodak suggested).
I used to run film tests similar to yours, using my camera and a white
board (and a small patch of cheese cloth for texture), but I gave that
method up many years ago. I found that it was not that accurate, was
time consuming and wasted lots of film. Now I simply contact a step
wedge under a filtered light source and run all of my development time
tests in one run. I can balance in a new film/developer combination
(N,N-,N++,etc. if you will) in 2-3 hours. It helps tremendously if
you have a meter that you can use to calibrate the light source that
you use to make your exposure since most of the manufacturers material
use lux/seconds (or some equivalent) for exposure values. After I
plot my curves I always run a confidence test using my camera to
verify my results.
Using a calibrated light source I have found that my curves are
surprising close to those of the manufactures, even when my "real"
film speeds are much lower. Indeed - I use their curves as a guide to
exposing my own. You might take a look at the published curve for the
film you are using and attempt to calculate the exposure required to
reach .10 above film base + fog and the exposure you used to obtain
the same - there is a good chance that the exposures will be very
similar. The ISO test for speed uses a much higher contrast curve
than what is normally used in the "real world."
Best -greg
On Tue, 8 Apr 2003, Scott Wainer wrote:
> Greg,
>
> I can almost live with whatever film speed I get. I thought that it might be
> about 1/2 - 1 stop less, I just didn't expect it to be 3-4 stops less than
> what the manufacturer rated it at. If that is truly the case then I will
> just go back to shooting Pan F+ (ASA/ISO 50) which gives me an EI of 32 with
> the same setup, chemistry, and processing.
>
> What I don't get is that all of the published data shows a higher EI than
> what I am getting; some times higher than what the manufacturer rated it at.
> Could my setup be that far off that I am loosing 3-4 stops?
>
> Scott
> smwbmp@starpower.net
>
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