 June Hyland |
ISO Film Settings On my camera(Canon EOS 3000)I can change the ISO speed. Can I change this film speed several times on the same roll of film ie... some sports shots using a hi speed; then some shots using slow speeds??
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Jon Close |
You can ..., but the film's sensitivity to light doesn't change. If you increase the ISO setting the autoexposure will set faster shutter speeds/smaller apertures, but this effectively underexposes the film. Print film generally has pretty wide exposure latitude, so that you can get useable (but not optimal) results from -1 or -2 stops underexposed up to +2 or +3 stops overexposed. Eg. for ISO 400 film you can rate it from ISO 1600 (-2 stops) to ISO 50 (+3 stops). If you make a wide variance in ISO settings frame to frame on a single roll you will need a very attentive printer to adjust the printing of each frame as the negatives will be of wildly different densities. Slide film has much narrower exposure latitude, generally giving useable results in the range of +-2/3 stops (eg. 400 speed film rated no higher than 640, nor lower than 250). Some slide films are amenable to "push processing", so that you can expose the entire roll at +1 or +2 stops and inform the lab to give the film that many stops of extra development. The film stays in the chemical solution longer to bring up the otherwise underexposed image. This cannot be done frame by frame, but for the entire roll only. The result usually has greater grain and more contrast than normally developed film. Increasing the exposure rating on print film is often called "pushing," but the C-41 print film chemistry generally does not respond to extra development time the way black & white and slide film does. The only advertised exception to this is Kodak's professional Supra/Portra 400 and Supra/Portra 800 print films.
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