Film testing

[Bruno Di Nunzio]

I would like to make a film test and I am planning to use Davis's method. I would like to have technical explanation about Davis saying that for a 100 ISO test we should have a 4 EV measure on the enlarger with f/11 and 1/4 sec exposure time. Details and math are welcome.

[Marco Frigerio]

Why not asking directly to Mr. Davis? ;))))

http://www.btzs.org/Forums/forum/default.asp?forumid=6

Ciao

Marco Frigerio

http://www.fotoavventure.it

[Chris Gittins]

I second Marco's suggestion to contact Phil Davis directly. I exchanged e-mail with him about a year ago re: film and paper testing. He was very responsive.

I assume you're using a 10 stop (21 step) step tablet. EV4 x 1/4 sec is a good first guess at the flux-exposure time product that will just get you above base plus fog on the second or third most dense step - can't remember if the most dense is Step 1 or Step 21. You want the exposure to be such that you can both see the toe of the curve and as many stops as possible beyond it. Figuring you want to establish your development time so something as 'extreme' as an N-2 scene, an N-2 will have nominally nine stops between Zone I and Zone VIII. You've only got 10 stops to work with on the step tablet, so you don't have a lot of latitude in how you expose your test sheet if you want to directly simulate an N-2.

In contrast to the flux and exposure time recommendation, the suggested f-stop isn't a critical variable. As long as you've got a uniform EV4 source, it doesn't matter how you generate it. I think I stopped down to f/16 rather than keep f/11 and raise the enlarger head further up.

EV4 isn't etched in stone either. Although I haven't researched it, I believe its recommended because the associated flux is in a good range to avoid reciprocity failure. I imagine you could work with substantially higher EVs if you trusted your timer to give you 1/125, 1/250, etc. exposures; use lower EVs and reciprocity can become an issue.

Regards, Chris