 Martin J. May |
Flash photography I own a Minolta 35mm xtsi. I took some flash pix at Christmas. I used aperture priority and closed the lens way down for max depth of field, probably f22. Used the built in flash on top of camera. They were all underexposed. (400 ISO film). I thought with aperture priority that camera would slow shutter down to get a good exposure. Doesn't an auto exposure camera auto expose with flash too? Won't it adjust shutter speed down to get correct exposure? Can you explain? Thanks.
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john m. ingram |
I do not see the advantage of stopping down your lens. Your depth of field is limited to only those objects equa distant from the flash. (Objects between your subject and the flash will be overexposed and objects behind your subject will be underexposed) The guide number, GN, for your flash (in the owners manual) determines the power output. The guide number is related to the aperture by the equation GN = aperture X distance to the subject. As you can see, stopping down to f22 reduces the flash to subject distance considerably. Example: Your GN is probably listed as ISO100(meters) 20. This means with ISO 100 film, the GN is 20 meters. So, if you are using f22 and ISO 100 film, your subject to flash distance is less than 1 meter. If you double the speed of your film, you gain 1 stop. In this case ISO 200 film would be like having f16 aperture and your subject to flash distance would increase to just over a meter. I would open up to my max aperture and shoot 200 or 400 speed film and you shouldn't have trouble any where in a normal house.
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