Originally posted by dh87 Thank your for your response. In auto, it does select high ISOs (1600 and 3200), but I reset it to 100.
That's not such a great idea. Do that in manual mode and you're forcing the flash to dump 5 stops of light, that wont look very good as it will give you the black tunnel look. Do that in a Av mode and you'll pay for it in far too slow of a shutter speed.
You are on the right track though, here's a cut and paste from a post I made on a similair issue.
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Yes that is typical, the camera is exposing for purely ambient light in auto or semi-auto modes, and does not take flash exposure into account in that mode. So, do not shot in auto or semi-auto modes whilst using pTTL on the flash unless you are only doing subtle fill flash. Indoors is not for fill flash.
So, put the camera in manual mode, ISO ~400 to 800, shutter ~1/100, aperture to taste. You want the meter to be saying you are under exposing by 1 to 3 stops. The flash should be in pTTL mode. Aim the flash preferably at a wall so light will bounce off that and illuminate your subject. Push the shutter. The camera will then instruct the flash to achieve overall correct exposure which it will do by adding the stops of light via flash that you are underexposing with your shutter/ISO/aperture settings. Then chimp and if your subject looks to bright or dim after this then use the FEC compensation on the flash to adjust. Typcially I end up dialing in -0.3 or -0.7 FEC. If ambient is too dark or bright then use ISO, aperture or shutter to adjust, this will alter the mix between ambient and flash but not the total overall exposure (only FEC will do this).
Remember, in pTTL mode the camera will use the flash output to achieve overall correct exposure. The more negative the meter says the scene is, the more light will have to be dumped by the flash to achieve correct exposure (hence the greater the ratio of flash to ambient). The less negative, the less flash will be dumped and the brighter the more the ambient light will show up.
All this sounds complex but is actually very easy once you try it and get the hang of it. The results are fantastic so it's worth mastering.
The best site I've found on using TTL mode on the web is this one
http://neilvn.com/tangents/. The think "the strobist" is the best site for off camera manual flash photography if you don't want to use pTTL.
Good luck and have fun experiementing