Erratic Exposures in Manual Mode (Canon 40D): Updated

It's definitely not the metering mode and I would be very surprised if it's a camera function doing that.

It will be either a fault with the iris or the camera not stopping down the lens correctly, looks like it's going too far and causing slight underexposure. I don;t know if it's electronic on canon lenses or mechanical but on nikon theres a little lever in the camera part of the mount that flicks a small lever on the lens end that closes the iris. It's possiblt that this may be out of alignment, bent slightly, the wrong size, underpowered by the camera in burst mode etc.

I would stick my neck out and say 99.9% it's a problem with that part of the system.
 
At a guess, is it anything to do with your card ?

Maybe the card can't cope with the file size at 6.5fps. Try reducing the file size and changing the CF card for a faster one.

I'm no guru on this type of thing, but it's worth checking before you do anything like sending it back to Canon.

Steve
 
Its to do with the burst mode isnt it? When using high speed burst the metering is not able to adjust itself quick enough in the short time between each shot. Were you using a semi-automatic mode (Av, Tv, P)? Pretty sure its this.
 
King_Boru said:
Its to do with the burst mode isnt it? When using high speed burst the metering is not able to adjust itself quick enough in the short time between each shot. Were you using a semi-automatic mode (Av, Tv, P)? Pretty sure its this.
Click to expand...

I think you should read the thread title :lol:
 
I think sporty and fletch are on the right lines here..

Do the test as Sporty says.. try to replicate the settings and focal leanth that this has happened at..

Then try a different lens.. id also try it with differnt focal leanths too and different appertures too.. If you do manage to get the problem to show its self, keep the settings and then try shooting slower then with a differnt apperture..

Good luck with it...

The only way it could be ANYTHING to do with metering modes is if there were an electrical fault in the camera thats causing it to.. Wobble.. (As in "Throw a") lol..
 
Agreed. It's unlikely to be the metering mode. More likely as has been suggested a few times, something to do with the fact we're using multi burst 6.5fps. At that speed some thing is sticking and not allowing all the light through.

I'll do more tests, esp at max aperture. If your theory is correct Ghandi, it shouldn't happen at max aperature, then it's the lens.

Thanks all for your suggestions, and I'll keep you posted.

Chris
 
Janice said:
i cant say Ive ever heard of that? tell me more!
Click to expand...


Just dug the manual out, its Custome function 16 (on the 30D), called "safety shift in AV or TV" and basically when its enabled it will overide your programmed shutter or aperture setting if over or under exposure is predicted by the metering.

Great for saving shots, not so good if the success of the shot itself is dependent on a particular value!!

Manual doesn't say if this is enabled by default, but think it is...

Its buggered me up a few times until I went looking for it and turned it off!
 
desantnik said:
Just dug the manual out, its Custome function 16 (on the 30D), called "safety shift in AV or TV" and basically when its enabled it will overide your programmed shutter or aperture setting if over or under exposure is predicted by the metering.

Great for saving shots, not so good if the success of the shot itself is dependent on a particular value!!

Manual doesn't say if this is enabled by default, but think it is...

Its buggered me up a few times until I went looking for it and turned it off!
Click to expand...

Safety Shift is also C.Fn 1-6 on the 40D and the default setting is disabled '0'
 
Just to give an update on the outcome of the erratic exposures. As correctly suggested is was down to a sticky iris in the lens. Infact, the problem did occur when shooting in any mode, not just manual. So for example in Av mode, despite to continuous exposures at the same aperture, shutter, iso, there would also be underexposures.

Under the warranty, I returned the lens to Canon Uk, and I've just received the lens back after having the iris replaced and the focusing recalibrated. Must say the phone support was good, and I receive calls back as promised, so they should be recognised for their service.

I haven't yet had the chance to try out the lens in anger at 6.5fps, but will hopefully get round to that soon. If as some have found, they are getting the same problem it might be the lens and not the body. That's a relief as I was worried that it was the 40D. Have to say the body has been performing brilliantly and am chuffed to bits with the camera. It's a great piece of kit.

Chris
 
Glad you got yours sorted, hope there are no reoccurences for you now.
 
Why can't I see the pictures in the first post? Just a list of camera settings.
 
Actually I removed the original photos and put them on the web so that canon could see the shots and the originals. If you're interested they're here at: www.walles.co.uk/canon

FYI, each set of sequences have identical aperture, shutter and iso settings. Some are taken in M, Tv, and Av, but with each of the modes the settings are identical.

Susie: Have you got anywhere with your issue?
 
Mine is being repaired, I tried my main lens on a different camera and there was no problem with any sticking, so as mine was still erratic with different lenses and the exposure was still shall we say odd it had to go back. I am awaiting the comments from them, but so far I have not heard anything.
 
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