My sensitometer is (or at least was) calibrated. I did use those Log-H equations to determine which step tablet density I wanted the speed point to fall. Worked perfectly.Quote:
Did you successfully make a test-strip at that exposure and have the speed-point land where you expected it on the test strip? What if you set the meter to ISO400, that should get it to read a larger aperture: f/1+0.7 at the correct light level (assuming the limitation is the meter's display and not its sensitivity).
Cheers for the PDF.
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. :)
Here's a graph showing the standard model of how the scene luminance fits on the characteristic curve. The log-H values are for a 125 speed film.
The proof for the ratio is with exposure meter calibration and how it relates to the metered camera exposure point.
Zone System: Meter Zone V, stop down once Zone IV (0.3), twice Zone III (0.6), three times Zone II (0.9), four times Zone I (1.2)... where you expect 0.1 density speed point to exist on Zone I (four stops below metered point)...
ISO: Meter, stop down 1 stop (0.3), 2 stops (0.6), 3 stops (0.9), 1/3 more stop (1.0)... where you expect 0.1 density speed point to exist at 3 1/3 stops below metered point.
Tell me... That's why I shoot TMY2 at 250 instead of 400... It's that simple?