Quote Originally Posted by polyglot View Post
As for f/0.7 for ISO400, that agrees well with these calculations rather than the BTZS suggestion. Hm = 0.002 lux-s plus 9 stops = 1.024 lux-s = -1.29AV, which is 1/3 stop less than f/0.7; or f/0.5+0.7 if your meter will read f/0.5 Did you successfully make a test-strip at that exposure and have the speed-point land where you expected it on the test strip?
f/0.7 proved to be too high exposure, and I had not enough of a toe in my tests. I estimated a new exposure, about 1.5 f lower, and that worked well for HP5+. I fudged it with 320TXP, which needed a little less exposure, about 0.5f, but I dialled down too much, and ended up having pretty toe but no DMax for the 4, 5.5, and 8 minute dev times.

I second Bill's suggestion to shoot just one sheet to test exposure. You can develop it quickly in a tray, even if the main test uses a tank etc. That's what is holding me back from doing it once more (3rd time!) for 320TXP: needing to do 5 tank-loads of several sheets, as I am lead to believe I would get incorrect results if doing less than the full load each time (I usually do 5 or 6 sheets at a time). Also, all of this testing is getting film-cost pricey.