Flash ratio

Without knowing the author's shorthand, it looks like the forumula for 2:1 lighting ratio, which is a typical, safe ratio.... esthetics notwithstanding.

In Nikon CLS flash system there are flash groups, named A, B, C. You can assign a different amount of lighting for each group.

Communication channels are numbered starting with 1.

Whatever it may mean, that kind of didactic statement can safely be ignored.

Photographic lighting is about using whatever method, whatever light placement, whatever tools and whatever ratios produce the required effect. And that doesn't include painting by numbers.

It is referring to speedlites, such as the canon ex series, that can communicate between a master and several slaves utilizing E-TTL flash control. In this case, A would be a key light, B would be a fill light, and C would be a background, rim, or hair light. The point is that light groups A and B are contributing to the lighting of the subject, and lgiht group C should be adjusted to whatever raito you desire for effect in reference to the sum of the other two groups. In traditional flash metering this would be akin to metering the key light alone, then the fill light alone to a stop or two lower, then meter the subject with both lights on for the aperture setting. Then adjust the background light relative to the last reading, if that makes sense.

Thank you all for your excellent expertise and willingness to share your knowledge. I've learned a great deal from this forum. Neil B.

James - just curious... How you explained it is how I think it should have been interpreted, however, in the canon system A is tied to the local flash which is almost always "fill" and B is the key light. Is the Nikon system the same?

Randy,

In the intrest of complete disclosure, I shoot Canon, but do not have any ex series flashes. A buddy of mine does and couldn't get them to work, so I read up them to help me. You are right, from what I recall. The A flash is the shoe mounted unit, which is usually fill. However, there are two(at least) other possibilities. First, if using the ST-E2(I think is the proper name) transmitter one could assign either the fill or key light could be group A. Secondly the units will let you adjust the output from something in the order of 8:1 through 1:8, which would change which was the more powerfull unit and therefore the key light; admitedly this example is really an exercise in semantics. In the end you are right, typically the A group is a shoe mounted unit and would be used as fill, good catch.

James,

I just obtained two Quantum x5d-r with the Qnexus adapters and have been playing around so am somewhat interested in the fill ratio question myself. Funny thing though, I had one Quantum set up as "B" for the key light yesterday and was in the process of playing with the menus. Unknown to me, my wife had taken the camera in the next room to take some photo's of things she was selling on ebay. She knew nothing about the setup and did not know to take the 550EX off of the master setting. I happened to be replacing a gel filter on the Quantum when she took her picture. I think I can still see the purple spot today :-) Ouch!