Camera Labs

I'm sure this is really simple. What is the impact on guide number by changing ISO? I had a quick search but haven't found a direct answer yet.

I'm debating if the Canon 430EX II is a significant upgrade from the Nissin Di622 I have. They're rated at 43m at ISO100 and 62m at ISO200 respectively. Would I be right in assuming it'll be a square law relationship, if so they're effectively the same power? 62/sqrt(2)=44

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.

Yes, you need to use the inverse square law.

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I take pictures so quickly, my highschool was "Continuous High".

I can't remember your exact reasoning for ditching the 622 but if you want more power have you looked at the Nissin 866? It is more powerful than 580EX II and has master capabilities too I think.

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Canon EOS 400D, EF-S 18-55mm, EF 24-105mm f/4L IS USM, EF 50mm f/1.8 MK I, EF-S 10-22mm, EF 70-200mm f/4L IS USM, EF 28mm f/1.8, EF 85mm f/1.8
Canon 430EX II, Manfrotto 055CXPRO3, Arca Swiss P0
Panasonic GF3, Panasonic 20mm f/1.7, Olympus 45mm f/1.8

MY FLICKR!

Ok, so it sounds like the power wont be any practically different if I went the 430 route. I don't really need more power, but I would like a faster cycle rate. I wonder if the higher power flashes will have a bigger charge store, so they could possibly have more flashes at a given output level than smaller flashes?

I hadn't considered the Di866. The main reason for going Canon was to get the ability to use the built in wireless control feature in the 7D. The Di622 only works as a dumb slave in that respect. The Di866 appears to claim to support the full wireless control so I guess it is an option too!

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.