Bounce Flash - ISO vs Flash Power

I have a 40D with a 580 EX2 and am trying to improve my flash skills as much as possible.

One question I have, is if there is a train of thought on which ISO to use.

E.G. Indoor shot, 10 foot white ceilings of people. Say 1/100 shutter speed.

Do you prefer to use 100 ISO, shoot to the right, and crank the flash up as much as needed, or try to use less flash and maybe do 400 ISO.

Shooting to the right seems to reduce noise as an issue to some degree, so I was curious what others do.

I generally like to get some mix of ambient light in the exposure and not just over power it with flash. In that case I'll bump ISO up sufficient to get the shutter speed I need at the f stop I want. In this case I'm almost always at least ISO 400 and work up from there. Scenario here is usually a wedding reception...

Keep in mind that using lower ISO causes your flash to need to output more light, so the batteries are consumed faster at lower ISO. Canon dSLRs are so noise free at ISO 400 there should not be a reason to shy away from that speed.

At less than full power it will recycle faster if you need that.

Yes, the closer you are to the correct exposure, the less noise there is except in the dark areas. I don't expect that you'll have any problems with ISO 400 if you're careful. These might help:
Some Volly Ball Tournament Tests **56K Warning!**

ISO test between 1Ds Mk.II, 1D Mk.II, 5D and 20D

The concept of "expose to the right" is really only valid in situations where you don't need to compromise on ISO. If you're cranking up the ISO to get a better exposure, you're defeating the purpose. All of the credible evidence I've seen shows that a properly exposed shot, at whatever ISO is necessary, is the best strategy.

When flash power is your limitation, the compromise is between aperture and ISO (shallow DOF vs. digital noise). Only you can decide what's most important.

I don\'t know about anyone else but when I bounce I have to use a +1 FEC PLUS ISO800 with my 580ex II.

I always thought the key tenet of Shoot to the right, was that you can properly expose at your target ISO, but then shoot to the right of that and you'll wind up with less noise at the end of the day.

Thanks for all the tips by the way. I hadn't thought too much about the ambient light factor, and it sounds like most people don't feel there is enough difference in ISO 100-400 on the newer canons to really make any sort of difference.

djscrib wrote in post #4931289
I always thought the key tenet of Shoot to the right, was that you can properly expose at your target ISO, but then shoot to the right of that and you'll wind up with less noise at the end of the day.

If you get that additional exposure with a slower shutter or a wider aperture, the strategy works fine when properly implemented. It increases the signal/noise ratio.

But if you get that additional exposure by boosting the ISO, you're introducing more noise with the higher ISO setting and cancelling out the advantage of shooting to the right.

good clarifiation curtis. I generally meant that I was simply dropping the shutter speed to shoot to the right in my example.

After some more reading it would seem the other problem with the high powered flash is the "dark cave" effect, and using the minimum flash required would prevent, or alleviate the need to drag the shutter.

Great input guys, thanks for all the tips.