Quote Originally Posted by Photo Engineer View Post
The ASA rating is pretty slow with all of the filtration, so I would start at around ISO 10 or thereabouts.
I have a large roll of 70mm print film for doing some experiments.
This material is very low in ASA. Making contact prints under the enlarger needs exposure times of 100-120 sec. with open aperture and a 150W enlarger lamp. RA paper is 20 times more sensitive.
The problem is that the normal exposure time at professional printing is very short (1/500s?). So you need a very very bright light source. With long exposure times, the Schwarzschild effect will multiply the required exposure time.
5-10 ISO could be a good value for highspeed printing. But when using a normal lamp, the effective sensitivity would be around 1 ISO or less. I calculated an effective speed of 0.5 to 1 when doing contact prints under the enlarger.
Maybe my material (Kodak 2383) is less sensitive because of age. I tried all kinds of developers, also self mixed ECP-2 (CD2).
The best and cheapest solution was using standard RA-4 developer (<1min dev.time), but C-41 will also work.

Joachim