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Dear all,
I should expose by contact a 21 step tablet on a TMAX 100 film under the light conditions defined by Phil Davis in his book, namely 4 EVs for 100 ISO to get a f:11 / 0.4 sec exposure.
I can get 4 EVs under two conditions:
1. when I measure the enlarger light with my exposure meter directly oriented to the lens. The enlarger head is about 72 cm height (29 inches) and the diaph is f:22. I suppose the exposure time must then be 1.6 sec. Is there not a reciprocity failure risk in those conditions ? Can I use the enlarger density filter to reduce the light and get f:11 at 0.4 sec in those conditions ?
2. When I measure with a spotmeter the enlarger light reflected on a white card. The head is then much lower: 48 cm (about 19 inches) and the diaph is f:8. Then the exposure time is 0.2 sec which is very short even for an electronic timer (apparently my timer can do it but I am not quite sure about its precision).
I can also have 4 EV at f:11 when the head is lowered at 34 cm (13.5 inches) but then the picture is out of focus.
Which combination should I use to expose the film ?
Maybe I missed something about this issue because the light measurement conditions (spotmeter on white card, meter directly oriented to the lens, ...) described here and there result in quite different lighting conditions ...
Thank you very much for your help.
best regards,
Philippe
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