I guess you would have to go back to dead reckoning after a fashion. First off b&w film does suffer from reciprocity failure. According to Kodak tri-x requires a 3 stop increase in exposure at an indicated exposure time of 100s and plus an increase in development time. You can find data sheets for various emulsions in their respective data guides. At least the kodak data guides contain this information. If you're using b&w film you can get acceptable exposures if you stop down the lens to about f8 for 35mm and and bracket around a 1 minute exposure time. don't bother making small exposure changes change by at least 2 stops and depend on the film latitude to help you out. Since you're using these long exposures you are probably taking photos of rather static subjects so taking a series of 5 shots would be my recommendation. True this doesn't exactly give you a determination of proper exposure but you should get one or two negatives with an acceptable range of contrast and detail. At 11:59 PM 5/27/2001 +0530, Ayash Kanto wrote: >Hi all! > >Recently, I started a thread on "Long exposures" and I got quite helpful, >creative replies from many of you. I shall like to thank once again to all >who contributed to that thread. > >As a continuation of that thread, I have something new to discuss and that >is the trick for determination of long exposures. > >My procedure is like this. I make changes in the ISO setting of the camera >and fool the lightmeter. Suppose, a film of 400 A.S.A. film is loaded in >the camera and the shutter dial allows a minimum shutter speed of 2 >sec. If the lightmeter shows an underexposure with full aperture at 2 sec, >I change the film speed to 3200 A.S.A., an increase of 3 stops and suppose >the lightmeter shows correct exposure at 2 sec with maximum >aperture. Therefore, for 400 A.S.A. the correct exposure will be 16 >sec. in principle. However, for colour films, reciprocity failure is a >significant factor to think about and therefore one should take care of >that. I don't know the situation for black and white films. Do black and >white films also suffer by reciprocity failure? If no, then f/4 at 16 sec >will give correct exposure with a 400 speed film. > >Recently, Todd pointed out that some of the older bodies like K1000 or >Canon AE1 are unable to measure the light using light meter for high speed >films and low shutter speeds like 1/4 sec. If that is the situation, then >the trick described above will be of no use to determine the duration of >long exposures. > >In that case, how shall I proceed to determine the duration of exposure? > >Any comments, suggestions, explainations will be well appreciated. > >With kind regards, >Ayash Kanto. > >- >This message is from the Pentax-Discuss Mail List. To unsubscribe, >go to http://www.pdml.net and follow the directions. Don't forget to >visit the Pentax Users' Gallery at http://pug.komkon.org .
http://antwrp.gsfc.nasa.gov/apod/ap010418.html
