Flash Exposure For Dual Flashes And Bellows

[Pete Gregar]

here is the set up.

Graphic view II 203mm/7.5 Optar with (X) sync Graflite flash mounted horizantal on front standard 1 flash on both ends. Vivitar 285 Vivitar 283

Both flashes have auto/manual modes. Would I set the 285 to an automode that correspondes to my 12 foot distance, the n set the 283 to the same automode?

So both would be on an automode that corespondes to a certain fixed distance and f-stop? Then the flashes automode will take care of the rest? Or will I need to compensate for dual flashes.

Will I also have to compensate for bellows extension.

I guess the easy way would be to use a flash meter.. Which I don't have. I hav e a minolta III if that would be any help.

thanks

[Erik Gould]

Here is what I would suggest: Set each flash to an auto range that covers the distance and f-stop you are using. The flash units will do the rest. Focusing at 12 feet there shouldn't be a bellows factor to compenstate for. The only thing to watch out for is an unusually bright or dark subject and/or background that will fool the sensors on the flash units. Do a test, but the setup should work just fine.

[Ellis Vener]

Setthe two flashes to manual; read the flash to subject distance scale for full manual power (for the ISO of the film you are using) on just one of the flashes. Since the 285 at normal angle of coverages (35mm or 50mm) is just about the same power as the 283. so close down to the next f-stop and shoot a Polaroid test. If the Polaroid film is a different ISO from the "real" film then you should use the Polaroid ISO to find the correct f-stop for the Polaroid and then you'll extrapolate the correct F-stop for the film. You might also try bracketing by extrapolating and then opening up a half stop from what looked good on the Polaroid.

[Ellis Vener]

Setthe two flashes to manual; read the flash to subject distance scale for full manual power (for the ISO of the film you are using) on just one of the flashes. Since the 285 at normal angle of coverages (35mm or 50mm) is just about the same power as the 283. so close down to the next f-stop and shoot a Polaroid test. If the Polaroid film is a different ISO from the "real" film then you should use the Polaroid ISO to find the correct f-stop for the Polaroid and then you'll extrapolate the correct F-stop for the film. You might also try bracketing by extrapolating and then opening up a half stop from what looked good on the Polaroid.

You don't want to use automode as the sensors will each see the flash from the other unit and you'll get premature shutdown of both lights.