Recently we've changed from TTL flash to manual flash to experiment a little bit. A recent article in Professional Photographer magazine has me a little confused. There was a formula for how much power a flash requires based on distance and aperture. It doesn't seem like different flashes should behave the same at say 1/4 power. If you had a big flash at 1/4 power, isn't that different than a tiny flash at 1/4 power? Help me out guys!
You have to know the Guide Number of the flash too to figure it out that way. That is basically the 'power' of the flash. Higher guide number is more powerful. Guide number - Wikipedia, the free encyclopedia Strobist: Guide Number: Your Free Flash Meter
Are you sure the intent of the article wasn't simply to describe the relationship between aperture, and distance? This is the same between various flashes. If flash A needs to be set at 1/2 at distance X, and at 1/8th at distance Y, then flash B will also need to drop the power by a factor of 4 between distance X and Y regardless of the power difference between them.
