Problem with flash in AV mode

[CeeCee]

I have had the 10D, 1D mrk2 and now the 1Ds mark2 and with all cameraes i have experienced the same - i might be the one who doing something odd ;-)

Here it goes :

When in AV mode i never get proper exposures - even when i use my 85/1.2L set @ 1.2 the flash fires as usual, but the shutter typically is 1/30 or even slower.... ??????

Why is that - its the same with the 420EX, 550EX and 580EX !!!!

What to do ?

[tim]

I always use M mode when i'm using an external flash. Av will expose for the background light level, not the flash levels. I use F8 1/80th, which seems to work ok usually.

[Patrick DR]

I have the same "problem" with my 300D. I started to get switched to M mode. I used P mode a lot but then i can not change my aperture if i want to.

[tim]

In P mode you can shift what it chooes by moving your dial. Move it one way and you get a smaller aperture and a longer exposure time, the other way does the opposite.

[pcasciola]

RTFM......:)

Av mode meters for existing light and the flash is used as fill.
Check the sticky post "Canon EOS Flash Bible" for more info.

From "The Bible":
Av (aperture priority) and Tv (shutter speed priority) modes set the shutter speed or aperture to expose for the existing light conditions correctly. They then fill in (http://photonotes.org/articles/eos-flash/index2.html#fillflash) the foreground using flash. If light levels are low you will need a tripod to avoid blur.

[phili1]

You can reset your custom function and it will default to 1/250 on the 20D, checck yours to see if it will do it as well.

But I use Camera on manual and it operates properly

[picnic]

You can reset your custom function and it will default to 1/250 on the 20D, checck yours to see if it will do it as well.

But I use Camera on manual and it operates properly
With the 10D it is 1/200---but if you have the 550EX and you could certainly set it for high sync and set it even higher in M.

Its already been explained why the shutter speed is so slow in Av mode. The camera is exposing for the background/ambient and the flash is exposing for the subject.

One other thing you might try is the method of using C.Fn. 4, setting it to #1 putting the AF on the * button and the metering on the shutter button. When you shoot, press the * button and then release it--you will get an exposure as if its in manual focus.

Chuck Westfall discusses the method here: http://forums.dpreview.com/forums/read.asp?forum=1019&message=7379947

[Patrick DR]

As a reaction to tim: yes i know that's the way iit works without my flash.
If i use my flash and for instand my 24-70,it directly chooses F/2.8 in P mode and won't let me change the aperture. Unless it's daylight and i want to use it as a fill in.
To bad i don't have a 20D or 10D :rolleyes: ,so no CF for me.