What am I doing wrong?

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Weggy

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Having an issue using a flash gun in Av mode...

Kit used is the 1DnMk2, with 24-105mm and a 580ex Mk2...

In Av mode, the image is badly overexposed, regardless of which aperture I'm choosing. Stick it in P mode, and the shot is perfectly exposed. Now, I really need the flexibility of being able to select the aperture, so any ideas where I'm going wrong? Is it a settings thing?
 
Are you making sure the flash is set on ETTL? It needs to be on that setting regardless of what mode you're in.

Make sure the flash output is set at 0.0

Keep the IS0 reasonably low - the lower the better for image quality and you should be OK.
 
Now, I really need the flexibility of being able to select the aperture, so any ideas where I'm going wrong? Is it a settings thing?
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I only ever use flash with manual control on the camera and the flash. For some reason I can't cant get the results I want letting the camera do the thinking and as for ETTL, it all seems like witchcraft to me.

As far as I can see, if you're using a digi setup with a histgram and preview with hightlight alert, manual is just quicker and easier. It takes less than a second to check a shot and make an adjustment if needed. Not only does this seem the quickest and easiest way of working to me but after a while you'll find you pretty much nail it first time too.
 
Weggy, my guess would be that the shutter speed needed to be faster than 1/250s for the correct exposure but because you were using flash the camera limited the shutter speed to 1/250s. Try again with the flash in high speed sync mode which will remove the 1/250s limit and you might find it all works.
 
I think pxl8 is correct in his assumption but also would take dazza's route. Manual will become more reliable once you get it nailed.
 
Most probably pxl8's suggestion, high speed sync should sort it.
 
I think we really need to know whether Weggy is shooting indoors or outdoors, and whether he's using flash as the sole source of illumination or just as fill in.
 
I have set one of the custom functions on my camera so the camera always syncs to 1/250 when flash is on. I rarely have problems since I changed this setting. However, during the day, I may use manual mode, and set manual exposure 1 stop under for the background of the main subject, and let flash do the rest.
 
CT said:
I think we really need to know whether Weggy is shooting indoors or outdoors, and whether he's using flash as the sole source of illumination or just as fill in.
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Shooting in Av the flash will always be fill.

Check the exif on your P mode exposures Weggy - are they all 1/250 or slower ? If the overexposed shots are faster than 1/250 in Av then it's a high speed sync problem.
 
Thanks for all the comments. I'll get the exif data tonight.


CT said:
I think we really need to know whether Weggy is shooting indoors or outdoors, and whether he's using flash as the sole source of illumination or just as fill in.
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Shots were indoors, and the 580 is the sole source except for a normal ceiling mounted house light, 60w I think....

Also forgot to say, the 580 is fitted with a stofen, if that makes any difference?
 
I've just tried some shots on my camera, in various modes. P shots are ok, Av ok (if I set customs function for flash speed in Av mode to 1/250 (otherwise slightly over exposed). Check you flash is set on ETTL. Also check flash exposure compensation on the camera and flash unit. The flash could be set at 0, but if the camera is at +2 it will over expose. This is seperate from the normal exposure compensation setting. I've noticed the flash settings overide the camera settings if the flash is anything different from 0. I'm using a 580 mk1 version.

Hope that may help.
 
If you're shooting indoors with the flash as the main source, don't use Av, this will always provide fill flash.

Stick the camera on manual at the aperture you want, then adjust the shutter speed so that your exposure is a stop or two below ambient - don't go too slow though or you'll get streaking of the subjects - say 1/40 or faster.

I usually have the flash dialled in at +2/3 (two thirds), as Canon flashes tend to underexpose.
 
natjag said:
The flash could be set at 0, but if the camera is at +2 it will over expose. This is seperate from the normal exposure compensation setting. I
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That's a good call actually - it could well be that causing the problem.

Weggy on the 1DMK2n press the button on the left top plate which you use to select the metering mode. That button also selects flash compensation. As you press the button, look at the exposure scale at the bottom of the LCD screen on the top right of your camera. You'll see the normal exposure compensation scale change to the flash exposure compensation scale. Just check that it's set at the centre point - no compensation. To be fair you should also be getting indication in the viewfinder too, but it's easy to overlook it.

The Stofen wont be the cause of your probs at all.
 
Think you guys may of found the problem... although I've since changed it, I have a feeling I had +2 dialled in as recommended by someone else for solving the 1d issue of underexposing...
 
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