----- Original Message -----
From: "I Zarkov" <dr_izar...@hotmail.com>
> Unfortunately the Kodak product search engine gives nothing for the topic
of
> 'reciprocity'which is too bad because they once had a very good chart in
an
> old professional products catalogue that gave a good long and short range
> adjustments for reciprocity [ i.e.: 1-10 sec and 10-100 sec ranges]. I'll
> see if I can find it somewhere else.
Zarkov,
TMY film needs relatively weak reciprocity corrections. If
you, judiciously, add between 25% and 50% more exposure for indicated times
between 1 to 10 secs, and between 50% and 150% between 10 to 100 secs, your
exposures should be -enough- well corrected. For non T-Grain films (i.e.
Tri-X), you'd need to increase the exposure 1200% for an indicated time of
100 secs. Clearly, the need for better charts is there more for Tri-X than
for TMY, for the range 1 to 100secs indicated, at least. I've seem the
chart you mentioned, you can still pull it from Kodak's site, here is the
URL (cut and paste it if it breaks):
http://www.kodak.com/global/en/professional/support/techPubs/f9/f002_0062gc.
gif
Another issue in the case of TMY and TMX, for that matter, is they (Kodak)
only gives us 3 correction values (1, 10, and 100). We need at least 3
points to plot a curve and that is what Kodak gives us (it'd be nice to have
at least y more between 10 and 100). Now, by seeing many other reciprocity
correction charts for other films, we know that this reciprocity phenomenon
is not linear but exponential, so we use that knowledge to plot a curve for
TMY based on the 3 points we have [( 1,1.25), (10,15), (100,300 )]:
corrected
time
|
P -------> (100,300)
|
_
|
_
|
_
| _
| _
| _
| _
| _
| _
| _
| _
| _
| _
| _
| _ P -----------> (10,15)
|_P____________________________________
^ indicated time
|
|
(1,1.25)
Once you have your graph, it is just a matter of drawing vertical lines from
the "indicated time" axis and from where this vertical line intersects the
curve, horizontal lines to the "corrected time" axis to find/read the,
reciprocity corrected time. Make no mistake, this 2 axis are photography's
"AXIS OF EVIL", I am, as we speak, writing Pres.Bush requesting military
action against them!
The same treatment can be made to any other film for which you know at least
3 corrections.
Guillermo
