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Slave Flash Problem Maybe Solved? So, I went to the camera store today and I described my issue: shadow outside on the face of subjects. He said to just use flash. I told him I did. Then he said that I don't know the secret then. He said that if I use Fuji NPH 400, I should shoot at 250 and then set my flash about 2/3 of a stop down. That will completely eliminate the shadow. Then, if I want a little shadow, increase the stop maybe 1/3 or so. Does this make any sense to anyone?
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Jon Close |
I'm not sure I understand your problem, so I'm not sure if what you were told will solve it, but it does make sense. If you originally used ISO 100 or 200 film, then changing to 400 will give +2 or +1 stop greater exposure to the ambient light background, and the flash output will be less. That would lessen the shadow from the flash. If you rate that 400 speed film at ISO 250 (+2/3 stop), you'll get an additional +2/3 stop exposure to the ambient background if the camera slows the shutter speed and/or opens the aperture by 2/3 stop (say from f/5.6 to f/4.5). If you do this and your flash is TTL then you have to set -2/3 flash exposure compensation on the flash to keep the flash from overexposing. If you have a non-dedicated flash then just leave it set for ISO 400.
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No. The shadow on the face was caused by the sun. I was using fill flash to try to get rid of that. The guy at the camera store said that the reason was I was using ISO 400 at ISO 400. He said you can virtually eliminate shadows by rating the 400 at 250. Then shooting the fill flash 2/3 stop less than that. I was wondering why I don't just increase the flash burst instead of going through all that. I'm not sure that what he said is correct. I am going to perform some controlled experiments. After this, I have a book that talks a little about this too. The book talks about doing experiments to find your true exposure rating. So, I guess the ratings on film are just a guideline. My question relating to that is if I shoot ISO 400 film at 250, do I tell the lab to process it at 250, or do I just let them process normally?
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Jon Close |
If it is print film, then just process normally. Print film has a wide exposure latitude; rating 400 film at 250 is the same as +2/3 exposure compensation. This will add detail to shadows, but it's not enough to worry about blowing out highlights. It doesn't hurt to experiment, but I'd be inclined to simply do as you suggested - add flash exposure compensation ("increase the flash burst").
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