580EX on camera Master with 420EX Slave

Easy question: I'm going to use my 580 on camera as a master on-camera with a 420 as a slave set off to the side on a tripod (as a key light).

If I set the 580 to "A" and the 420 to "B" as the instructions say, and I set the ratio to 1:3, say, what is 1 and what is 3? Plus, if I use the on camera flash for fill, and it's 3 times further away than the 420, what should the ratio be? 1:3 or 3:1, and what does this mean?

For portraiture, is there any value to using Omnibounces and bouncing flash or should I jst fire straight on? How about for interior work?

Phew!

Thanks

1:3 means that your B flash will be 1 1/2 stops brighter on the subject than the A flash.

Since ETTL will account for the distance of the flashes (within limits), it doesn't matter how far the flashes are from the subject. What matters is how much light falls on the subject and as long as the flashes are near enough so that the set amount of light falls on the subject, distance will not enter into the equation.

For portraits, diffused lighting is always preferrable to straight headon flashes, I think.

My portable setup is a 550EX on a light stand, with an umbrella, and a naked flash on the camera (which I might get around to diffusing one day). I usually use a 1:3 ratio, but I experiment between 1:2 and 1:8 depending what i'm doing.

The best thing to do is plan and see what happens.

I was under the impression that flash to subject distance would affect ratios. The pre flash fires them all evenly and determines what total output is required, then tells each slave group what part of the required output to fire at. So a ratio of 1:3 (A:B) If B is further away you will (depending on distance) get a ratio more like 1:2 or 1:1.

I'm with pacace on this one, I don't think subject distance is relevant since ETTL takes that into account.

Guys, thanks for the replies, however the confusion that exists even in this thread is why I am in such a quandary.

I'll stay tuned...

Dennis

Good explanation here

With wireless remote, there are two ways you can do it. In full ETTL auto mode, in which case distance will not enter into the equation (within the lmits of the flash's working distance) because it has already been accounted for by ETTL. And then there's manaul wireless mode. Here, you control the flash ratios by setting the strength of each flash independently. And in this case, distance is an important factor because flash strength varies with distance. However, the 420EX can not be set to manual mode so it can't be used as a manual wireless slave.

Ace, so in ETTL, do I NOT set the ratio? Or do I set it to 1:1?

Well, whether you want to use ratios or not depends on how you want the different flashes to interact with each other. For example, you might want to take a portrait shot with the key lighting about 1 to 2 stop brighter then the fill lighting. In this case, you will need to set the ratio to something other than 1:1, otherwise you are going to end up with flat lighting.

If you haven't already, take a look at the link that Rene provided above. You'll find more helpful info on ratios there.

After reading up on it some more as well as doing some test shots of my own I've realised flash to subject distance is accounted for and wont affect raitios. My bad

We're all here to learn