I feel like a complete idiot...

But whenever I am in AV mode and use either the pop-up flash on my 20D or attach a hot-shoe flash, my images come out way overexposed. I'm using ETTL on the flash, and thought the 20D and the 508EX would talk among themselves and figure out exposure, but, NOOOOOOOO, it's as though they spoke entirely different languages.

Anyone care to make me less idiotic?

Thanks

Dennis

You can be anything but idiot as iditots never ask....

You need to go through a check list of over exposure.
First I would like to know little more about your problem, and how camera handles other situations, apart from explained.
Are you sure you have not set EV wrogly? i.e. EV in + range, 1, +1 +2 etc. You should be seeing this by looking at the bottom of your view finder or LCD. Arrow or dot should be on zero. 1st put camera in the mode that does overexpose and check for this.

Samsen.

Sam - Thanks. No EV.

All works fine until I turn on the flash. I use AV all the time outside for sports, and use M for sports with flash at night (either exposing with the in-camera meter or using a hand-held Sekonic 358 ) under ETTL, but had never used AV with flash before, despite having taken some 100,000+ shots over the past year.

I just shot another 800 shots today in AV at a youth baseball tournament with the same settings, minus the flash.

Dennis

I'm going to assume that you were using Av mode outside in broad daylight and had the aperture set low so that your shutter speed was faster than the max sync speed. If that was the case, the moment you slap on the flash and it's not in HSS mode, your shutter speed is going to drop down to the max sync speed. That alone will cause your picture to overexpose even without adding the output from the flash.

What you need to do is watch your shutter speed and aperture in the viewfinder and see if either of them starts to blink to indicated an overexposure problem.

Hey, yeah, this could have been the case.You mean the camera would choose 1/60 as the sync speed?

I was trying to use the flash for fill. It wasn't what I would call "broad" daylight, but it was the middle of the day, but in shadows. So, if I went into HSS it would work?

IIRC, though, this also happened inside - that is, the images were overexposed. I'm using a EF-S 17-55 f2.8 IS, and I might have had it fairly wide open, so I guess I could have also been in an overexposed mode by dropping the shutter speed down for flash.

Maybe it's time for me to read my manual about how to do fill flash?

Can't call myself anything but a learner for flash photgraphy, but what I have learned is that using any auto (Av or Tv) setting will result in the camera trying to expose the whole frame as though there isn't going to be a flash - then during exposure, the flash puts out enough light to ensure the coverage area is sufficiently exposed. This I've found leads to either slow shutterspeeds and blurry backgrounds due to shake, or overexposure. Having tried manual settings on the camera I find it leads to much better shots. - usual rules apply, 1/250 and F8 should give enough depth of field and handholdability then the flash does the rest in terms of outputting enough light to get the exposure correct.

I'm another beginner with flash but don't forget that when you have sorted your shutter speed problem out you can still have control over the flash output by using "Flash Exposure Control".

If you are using AV mode and flash for a little fill you will probably have to dial in negative FEC on either your camera body or speedlite to avoid overexposure.

Check out the following link. It helped me get my head around the fact that when you are using flash it's two independent exposures really.

http://www.photoworksh​op.com/canon/speedlite​/index.html

One for background/ambient light which you have control over and one for the subject (the flash) which you have separate control over using fec.

mapollo wrote:
I'm another beginner with flash but don't forget that when you have sorted your shutter speed problem out you can still have control over the flash output by using "Flash Exposure Control".

If you are using AV mode and flash for a little fill you will probably have to dial in negative FEC on either your camera body or speedlite to avoid overexposure.

Check out the following link. It helped me get my head around the fact that when you are using flash it's two independent exposures really.

http://www.photoworksh​op.com/canon/speedlite​/index.html

One for background/ambient light which you have control over and one for the subject (the flash) which you have separate control over using fec.

Good point about FEC. Had forgot about that. Kinda after the fact, but I did look at my histrograms.

Thanks,
Dennis

PacAce is right.... Use HSS

Yup, its a very simple fix. Simply turn on High Speed Sync on the flash. I belive the 580ex and 430ex both support it. If you want a good explanation of what this is, and why you should bother with it, then read here

http://www.rpphoto.com​/howto/view.asp?articl​eID=1026

most definitely because you are not using your high speed sync.

I did the same thing when I first got my flash

The problem here is that you trust the equipment to get it straightened out. I could never trust directions in a foreign language. Learn to speak camera/flash and you're all set.

Another option that will prevent this from happening is to use the "Safety Shift" custom function. It will automatically stop down the aperture as needed when flash forces the shutter speed to 1/250.

Cool. Is this a CFn on the 20D?

Yes. C. Fn. 16.