From: Richard Knoppow on 24 Jul 2010 03:05
"David Nebenzahl" <nobody(a)but.us.chickens> wrote in message
> After my recent success with TMX, I delved into my
> freezerful of film and pulled out a roll of Pan F I want
> to shoot. But I'm a bit mystified by the enclosed
> processing instructions.
> Was thinking of using D-76, and they have times for both
> this and ID-11 (same times, since the same developer,
> except that they list ID-11 at 1+1 but not D-76, though I
> assume I can also dilute it). But they show the same times
> for both ISO 25 and 50 exposure. Can this be correct?
> Other developers show different times for the two speeds.
> They also show times for Perceptol, but not Microdol-X.
> Richard K., you said these developers were equivalent:
> would you use the same times for both of these? The
> Humumgous Massive Really Really Big Dev Chart
> (http://www.digitaltruth.com/devchart.php) shows different
> times for these (9 min. for Perceptol vs 12 min. for
> Microdol; should I just use their recommendations?
You will notice that Kodak also rates T-Max 100 and 400
at double speed with normal development. The differece
between the two exposure indices is a difference in overall
density and in shadow detail, the contrast remains the same.
When the ASA system of speeds was introduced in 1943 it
included a safety factor of two so that all film speeds were
half the value actually determined by the test method. For
some reason this was thought to be a good idea even though
the research at Kodak from which the standard was adopted
was intended to find the _minimum_ exposure possible for
good tonal rendition. This was because film is somewhat less
grainy and somewhat sharper for thin images. Nontheless, the
lower speeds were recommended. I think the reason is that
Kodak, in particular, wanted to insure amateur users would
get a printable image and overexposure does less damage than
underexposure. In 1958 when the ASA adopted a modification
of the then new DIN standard, which was much easier to
measure than the minimum gradient method previously used,
they also dropped the fudge factor and all film speeds were
doubled! That put the manufacturers of "magic" speed
increasing developers out of business. They all knew and
counted on the fact that all films were actually double the
speed given by the ASA. Kodak actually talks about this in
the introduction to the film booklet included in the _Kodak
Reference Handbook_ but its obscured by recommending
increased speed only to essentially professionals.
In any case many photographers find that increasing
exposure from that given by the ISO speed often results in
better shadow rendition and, with modern thin-emulsion film
has little effect on grain or sharpness.
Los Angeles, CA, USA