[alt-photo] Re: Your Approach to Making Negs for Platinum Printing? Ideal Negative Contrast and Dmax?
photographeur at nerdshack.com
Sun Oct 9 03:33:11 GMT 2011
>I'd like to ask for one more clarification. The step size on a 21-step
>tablet is 1/2 a stop and a 31-step tablet is 1/3 stops. These equate to 1/2
>stop equals 0.15 and 1/3 stop equals 0.10, correct?
They vary -- each manufacturer typically makes a number of different
step wedges (also called step tablets) for different purposes, each
with a different number of steps and a different step size. You
should get the one you need, with a total range greater than 2.4 (3.0
is usually sufficient for Pt, although I've seen cases where the
process ES reached nearly 3.0 -- if it turns out that your process
does, you will want a wedge with a bit more range).
One stop is log (2), or 0.301 (usually rounded to 0.3). So yes, 1/2
stop is 0.15, and 1/3 stop is 0.10 (round figures). Stouffer is one
reliable supplier -- Kevin Morris of Stouffer is on the list, last I
knew. They make both a 21-step x 0.15 wedge (T2115) and a 31-step x
0.10 wedge (T3110), each of which has a total range of 3.05. These
are the two most often-encountered wedges, and either would be ideal
for your purpose. If you need more range (it is possible, as noted
above), Stouffer makes a 41-step x 0.10 wedge (T4110 -- total range,
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