Canon 20d and flash sync mode

Why is it that I get better results in AV mode when the flash sync on my Canon 20D is on 1/250th second instead of the default auto? When on auto the pictures are under developed when using the built in flash.

If you want definitive answers you need to post examples in both modes. The pictures should contain EXIF information, which will tell us what the camera's done. I don't use auto modes so I have no idea what it does in those modes.

In Av the camera meters for the background and uses the flash as fill. You should try manual mode, say ISO400, F5.6, 1/250th, then F2.8, 1/50th, and take a look at the difference. ETTL does the work there.

That's your camera's way of saying "get a friggin external flash on me, I'm naked!"

In my opinion, the built-in flash is totally useless. You will have MUCH better results with one of the EX series Speedlites.

It is particularly important to get one of the models that can swivel and tilt to allow bouncing off the ceiling, walls, or reflectors that you put into position. Some of the older (and cheaper models) don't/didn't have the total swivel and tilt capability.

Probably because normally it's using the flash to fill in a bit on the available light exposure, but when you're using that CF (3-1?) it's been told that it won't be getting available light, so it makes the flash primary.

I find the built in flash ok if all I need is a bit of fill, it's a bit harsh but ok if I don't bother to take along an external flash - eg to a party. I almost always take a flash though, the 580 is so much more versatile.

Thanks for the responses. It just seems that when indoors things are a bit underexposed if I use "auto" flash sync under custom functions while using AV mode. I borrowed a friend's 420ex and got the same results. Granted this is in a room that has a low light level.

>>It just seems that when indoors things are a bit underexposed if I use "auto" flash sync under custom functions while using AV mode. I borrowed a friend's 420ex and got the same results<<

Very typical and widely spread complaint when using Canon ETTL flash as primary source of light. General wisdom to overcome this inadequacy of the ETTL implementation is merely to dial in FEC = 2/3EV or 1 EV, and 'learn to cope'.

White or light walls in most homes will cause ETTL to underexpose by a stop or so.