An easy method is to double the film speed for the first shot and double it again for the second. For example, if you are using, say, Delta 100, your first shot would be taken with your camera set at a film speed of 200, then you would change the camera film speed to 400 and shoot the second one. For a third exposure you would double the 400 to 800.
Several weeks ago I went out to shoot amongst a crowd of tourists with the intention of capturing some double and some triple exposures. I set the 180mm lens on my Leica R8 to f/4 and the metering to matrix. I pressed the button atop the R8 which prevents the film from advancing, thus allowing multiple exposures until it is released. The attached photo was obtained on Technical pan film. Since I was shooting Technical Pan at ISO 50 rather than 25, for the first exposure I doubled it to 100, for the second I doubled that to 200, and for the third I doubled that to 400. I had been laughing while watching people fiddling with the control buttons on their digital cameras, seeking help from others around them, observing many extending their fingers and arms all over the place, and banging into others as they went into a semi coma attempting to use their tiny digtal camera displays and viewfinders, missing many shots in the process amidst their confusion. I realized a triple exposure would successfully capture the confusion around me and that is what I accomplished. It is great fun seeking source material for double and triple exposures! You must remember,though, where the main point of interest was situated on the first shot in order not to wipe it out with a point of interest on the second shot. Like mastering all photographic skills, practice, practice, practice.
Last edited by tbm; 08-21-2007 at 12:55 PM. Click to view previous post history.