Hi, I haven't found the answer to this issue: if I place two SB-600 together and fire them simultaneously at maximum power, will they deliver more power together than 1 SB-800 at full power? And if so, by how much? The Sb-800 is supposed to deliver 1 step more power than the SB-600.... sorry, I suck at math! Thank you

Based on Nikon's guide numbers, the SB-800 is +2/3 stop over the SB-600. Yes...The photon energy of light is additive...In other words, two strobes fired at the same energy level will produce twice as much light as a single. Basic physics here...just as two 100 watt light bulbs provide twice as much light than one. So you can take the GN of the SB-600 and multiply by 2.

Yeap to double the GN you need 4 times more energy. Has to do something with some square laws or whatever...it has been a while since l left a classroom I bet Andres is now totally confused.

if you fire them not attached to a camera, the two sb-600s will produce more power than a single sb-800. ........attached to a camera, that will be a totally different explanation.

Bob and Frank are right. I remember reading something like this on strobist, talking about multiple SB-800s for use with FP sync. But it basically goes like this. Given a set of identical flash guns firing at the same power, compared to a single flash gun at the same power, the gains go like: 2 flash guns: +1 EV stop 4 flash guns: +2 stops 8 flash guns: +3 stops And so on, in powers of two. Physics is a pain.

Bob, Is there a physics reference to this? 1.4 sounds like a log number to me. +1 EV makes sense, but what say you on the additive properties of light? I don't want to turn this thread into a physics lesson, but am still curious about some reference material.

You combine guide numbers by taking the square root of the sum of the squares. The SB-800 guide number is 125, the SB-600 is 98. Two SB-600's would be: sqrt of (98x98)+(98x98) or 138. So yes, two SB-600's would be very slightly more powerful, but the difference would hardly be noticeable. If you do a little math manipulation of the equation, you can see that when the guide numbers of the two flashes are identical, this is the same as multiplying it by the square root of 2 (1.414). The general formula works for combining any number of flashes with different guide numbers.

Yes it is physics, and 1.4 is the short form of the square root of 2. Doubling or halving the light equals one stop difference. So one way to calculate the new guide number for two identical flashes is: GN of 100 gives you f4 at 25 feet. Doubling the light would be f5.6 at 25 feet, so the new GN is 140. Divide 140 by 100 and the answer is.... 1.4.