Quote Originally Posted by kwmullet
Given the absence of LF film >iso400, would it be reasonable to say that the Mortensen method might be one way to find out what my greatest working exposure index between 240 and 8000 might be? Is the goal with this method to develop the film as long as possible until just before you get to an unacceptable level of base + fog?


Final question (for this post, anyway) -- what kind of film would likely yield a higher effective speed: the one with the highest ISO rating, or the one with the lowest base + fog?

I've found that most modern films/developers do very little after a half-hour or so. When I tested max push shadow speed a few months ago I found the 400s grouped pretty close, with HP5 generally 1/4 stop ahead, Tri-x 1/4 stop behind, D400 and TMY in the middle. I've been happy with stuff I've shot at 4000 on TMY (my choice of 400s because I mostly shoot available darkness on 6x9, where grain and acutance are a bigger deal than 1/4 stop of shadow speed.) Stand/other compensating development seemed to offer no shadow speed advantage vs. more mainstream options, but allowed max possible shadow speed without sending the highlights into orbit. T-Max RS developed around 15 minutes offered a tiny bit more shadow speed than everything else I tried (Xtol 1:1 stand, Microphen, Speedibrews, Acufine) but gave truly horribly blown highlights. Microphen gave the best highlight control, but I liked the grain and acutance of the dilute Xtol better.

I shot multiple sets of step wedge on 35mm, 6 shots per set, opening the camera in the dark to cut a slit between sets. I had a scale below the target that I marked the EI on by moving a piece of black tape. I developed strips from several different films on one reel in whatever the developer du jour was. A little more work, but a lot less film than burning a sheet of 4x5 for each test.

The only film I had trouble with losing speed into the fog was D3200, and it was definitely temperature related. But none of the others did this--TMY and TMZ worked great at 20 minutes stand in Xtol 1:1 at 95F. A little more fog, but resolving the same steps they did at 30 and 45 minutes at 72F.