 Robert M. Dutton |
Sync speed and aperatue using flash I am slowly aquiring studio equipment for my home/ portable studio set up. Because of my limited budget, it will be a long time before I can get a good flash meter. How and Do I need to incorperate X speed in my GN calculations for aperature. Also do GN calculations change when using a white reflective umbrella; does the flash lose some of its power as it bounces?
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Robert M. Dutton |
I must add the reason for this question is because I just got my first slave flash (GN 90ft) with reflective umbrella (thank g-d for ebay).
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
need to worry more about aperture than sync speed. sync plays more of a role with ambient light than flash. Yes light does loose intensity when it bounces. How much depends on the surface it bounces off of. until you get a flash, you'll have to figure a reference point with your umbrella. Find what's the correct exposure at a power level at a certain distance like full power at 10 feet away. Then based on that you can determine what the exposure should be at different power levels, and at different distances. If the exposure at 10ft. with full power is f/11, then if you use half power, you'll know to be at f/8. and you can determine different distances at different power levels.
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Jon Close |
The shutter speed (so long as it is x-sync or longer) does not matter. The flash duration is much much shorter, usually on the order of 1/500 to 1/10,000 sec. so that the flash exposure is the same whether the shutter is open for 1/125, 1/30, or 3 seconds. The flash exposure calculation involves only the speedlight guidenumber, flash-to-subject-distance, film ISO and lens aperture. f = sqrt(ISO/100) x GN / D The guidenumber is reduced when bouncing into an umbrella since not all of the light is reflected, and it is dispersed over a wider area. Not possible to know the amount of reduction without testing with a flash meter, though the umbrella maker may (or may not) have some info on this.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
I wouldn't say it dosen't matter at all because you can't shoot a sync at 3 seconds and not have it matter. Unless it's absolutely no light in the room.
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Robert M. Dutton |
Thank you for your input. It looks like my next purchase will be an inexpensive ( possibly LED) light meter. Since the X speed is really not a factor, I think I can get by with one of these models.
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