HELP !! am currently using a toyo aII 4x5, with a 105,150,210 lenses,using t-max 400 & t ri-x pan professional, is there a simple formula for long timed exposures from 1 minute to ???
Not really. Your best bet is to test. Find a subject you won't mind looking at f or a long time and making a bunch of prints of. Next step make some exposures. S tart early enough so that you don't run out of light. Try you first exposure at somewhere around the time you get a 15 second exposure. Now if your meter indica tes a 15 second exposure, make one at 15 , 30 , 60 , and 120. You might even wan t to put a card in the image that tells you what exposure the negative is, or ma rk the holders to keep them straight. Now wait until you get a 30 second exposur e, by your meter, and do 30, 60 , 120 and 240 seconds. Now you have gone from 1 5 seconds to 4 minutes. If time allows and the light holds, go from 1 minute to 2, 4 and 8 minutes.
Now that you have the exposed negatives, process them normally and proof them, I think you will start to see the effects of increased exposure under low light c onditions. Your next step might be to see what N+, or N-, processing will give you under the same circumstances. Keep detailed notes of the light readings, exp osures and any development compensations you make and you will learn just what e xposures will work for YOU and your style of photography.
There maybe other systems that will work as well, this one is time consuming, an d takes some film to do , but the results are tangible. You can see the effects of lengthy exposures. I know now, by having actually done this test, what exposu re compensation I must make when I have a 1 minute exposure, or 2 or 4, indicat ed by my light meter, and whether I will need N or N+ developmnet to accomplish what I want to.
richard in seattle
actually yes there is a source of information. on page 32 of the book ''KODAK PROFESSIONAL BLACK-AND-WHITE FILMS'' there is a chart that shows the required exposure time vs. the caculated time. it starts with one sec, and goes up to 105 sec. of caculated times. next it tells the actual required time to account for reciprocity. ie. a 30 sec. caculated exposure requires an actual 200 sec exposure. on page 31 the book gives a brief idea of adjusted developemnet times due to the long exposure. ie. a caculated exposure of 10 sec requires an adjusuted exposure of 50 sec. and an adusted development time of minus 20%. hope this helps richard in seattel
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