If I'm inside and can use the ST-E2 or another 580EXII (with Ray Flash) as a fill, I'll use E-TTL.


I like the ST-E2 because it is very simple and fast to change the ratios of the key and fill (you have to assign them groups). Then you can control the power through the flash comp on the camera all in a matter of seconds where manual it would take some time and some wandering. Clients seem to loose patients and confidence if you are running back and forth changing settings (if I have and assistant to sit in before hand this is not a big deal). If I do it from the camera they don't even realize anything is going on.


Another reason I like it is, I can shoot a portrait at say, f/5.6 but then I decide this subject would look really good in an artsy shallow DOF shot. I can crank the f/stop down to 1.2 and the E-TTL will compensate without having to readjust lights for several minutes. I can go back and forth with any f/stop, shutter speed or ISO and my lights will be consistent. I find this invaluable.


The one place this bit me in the butt was one day I was shooting a headshot and I set my normal shutter/f-stop and forgot to change my ISO and I started shooting at 1600 and normally it would be blown way out on the LCD, but in E-TTL the flashes were adjusted so I didn't see the mistake until later.