On 06/22/2018 04:38 PM, `Richard Knoppow wrote:
Thoughts:
1) One thing I discovered in developing the correction tables for the
temperature controlled timer I was working on is that - at least for
conventional film/dev combos - the correction for time and temp is
pretty consistent across them as a percentage matter. When I compared
formula driven corrections against table data provided by Kodak and Ilford,
the formula was pretty close, at least between 60F and 80F which is what
the timer currently targets. "Close" means less than 10% or so variation
from published values - essentially negligible (unless you are a BTZS
fiddler who likes doing sensiometric testing more than taking pictures :)
2) In my own experience, treating conventional films of a given ASA
as being the "same" for purposes of figuring out the nominal development
time is pretty close. For example, I didn't have data for Arista 100
in PMK. So I used my Agfapan in PMK values to get started because both
are nominally ASA 100 films (and both test at a "real" ASA of about 50 on
a densitometer when processed in "normal" developers like HC-110). This was
essentially right on, or close enough anyway.
3) So, for everything except tabular films, if I get an alien film for which
I do not have data, I just use another film of similar ASA to get going,
and the same time/temp curve for everything.
I used to be meticulous about testing every new film/developer combo I
tried with the densitometer. But ... it seems to just not be all that
necessary unless I get very strange or unexpected results. Modern films
have huge latitude. The usual sin committed is underexposing them. But
if you hold shadow detail and don't let the highlights blow out, you can
easily correct minor development variability in the printing process. At this
point, I pretty much just use these rules of thumb for everything and it
works remarkably well:
a) Expose film at half rated ASA
b) Find nominal 68F time for that film, or other similar ASA rated film.
c) Underdevelop 20%
d) For each -+N adjustment, decrease/increase development time 20%.
Perfect? No, probably not. But I get consistent and easy to print negs
this way.
--
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Tim Daneliuk tundra@xxxxxxxxxxxxxx
PGP Key: http://www.tundraware.com/PGP/
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