Push & Pullgreenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread
anybody got and general formula for the alteration in the develping timmings for push and pull processing? Thanks shree
-- Shree (email@example.com), April 03, 2000
No general formula will work for all developer/film combinations. I use the zone system. With D-23 1:1 and HP-5+, a one-stop pull (N-1) is 86% of normal, a two stop pull (N-2) is 68% of normal. A one-stop push (N+1) is 145% of normal. And a two-stop push (N+2) is 200% of normal. I arrived at these numbers by testing. They may not work for any other combination.
-- William Marderness (firstname.lastname@example.org), April 03, 2000.
In fact, it would be mere chance if they did. It is a good idea to start your own experimentation on the basis of manufacturer's recommendations in data sheets. Even most of today's data sheets repeat that disclaimer: "The values given depend on your individual processing, and may vary by ...% in either direction." A typical percentage is 15%. Depending on film and developer, 15% can be a lot or a little.
-- Thomas Wollstein (email@example.com), April 04, 2000.
I use 20% as a starting point.
-- Robert Orofino (firstname.lastname@example.org), April 16, 2000.