1D Mk IV: Strange shot-to-shot brightness variation

[Joerg Rockenberger]

Hi,

I have a rented 1D MkIV with me at Bosque at the moment and I observed earlier this week something strange with regard to a variation of the brightness/histogram of images taken in a burst. First the basics: I am shooting in manual mode at fixed ISO with the 500F4IS and have the AF drive at the low or high speed setting. The AF point is central (w/ surrounding AF assist points) and AF mode is AI Servo.

It occasionally happens that subsequent images taken within the same burst (and hence same scene) vary slightly and alternate in brightness. The effect is also clearly visible in the histogram. The variation is usually normal/brighter/normal/brighter etc. Normal being the brightness I'd expect based on the selected exposure parameters. Brighter means that the image is about 1/3 of a stop or less brighter than expected.

Has anyone seen this? More importantly: does anyone know how to avoid/fix that?

Thanks. Best, Joerg

[Roger Clark]

Joerg,

Do you see any residual banding in the images? If the brightness is uniform over the whole frame, at least the image should be easily recoverable. The camera does not appear to be operating correctly. You might complain to the place you rented it from and see if they will send you a replacement. Explain you are in the field on a shoot and need a replacement asap. They should send you a new one by fed ex at their cost (my opinion).

Roger

[Don Railton]

Hi Joerg

Is it possible you have the Exposure Auto Bracketing turned on? If you can see 3 small overlapping squares of different shades of grey in the top LCD display then this could be the problem. Note that these squares are not the same 3 overlapping squares used for indicating multiple shutter actuations (hi or low speed you refered to...)
If so, to cancel EAB then hold down the MODE <MODE>and AF.DRIVE buttons <AF.DRIVE>simultaneously and turn the top wheel until the 3 dots under the exposure scale converge to '0'.

DON

[Joerg Rockenberger]

Joerg,

Do you see any residual banding in the images? If the brightness is uniform over the whole frame, at least the image should be easily recoverable. The camera does not appear to be operating correctly. You might complain to the place you rented it from and see if they will send you a replacement. Explain you are in the field on a shoot and need a replacement asap. They should send you a new one by fed ex at their cost (my opinion).

Roger

Thanks Roger for your assessment. No discernible banding is visible but I haven't played yet with the exposure in ACR to see if it's there. I agree that it should be possible to recover them but it's still annoying.
I've contacted the rental service earlier this week but they didn't have another MkIV available this week.

Best, JR

[Joerg Rockenberger]

Hi Joerg

Is it possible you have the Exposure Auto Bracketing turned on?
DON

No. If AEB was activated you'd also expect a sequence like normal/brighter/darker or similar. JR

[Don Railton]

Hi Joerg

Seems I have misunderstood... I thought that is sort of what you were describing in your second paragraph..

good luck

DON

[Sidharth Kodikal]

Joerg,

Not sure if it's the exact same symptom, but check out pane #3 here

http://www.birdphotographers.net/forums/showthread.php?74604-My-thoughts-on-the-Mark-IV

[Jim Michael]

Does the exif data support the belief that all exposures were the same? I'd try a quick test shooting a sequence of a white sheet of paper and examining the images and the exposure data.

[Joerg Rockenberger]

Joerg,

Not sure if it's the exact same symptom, but check out pane #3 here

http://www.birdphotographers.net/forums/showthread.php?74604-My-thoughts-on-the-Mark-IV

Sidharth,

Thanks for the link. The exposure variation I saw is not at all as strong as what Robert experiences. It's not clear from his description if the variation is alternating as I saw. On the other hand, the fundamental cause may off course be the same.


Does the exif data support the belief that all exposures were the same?

Of course.


I'd try a quick test shooting a sequence of a white sheet of paper and examining the images and the exposure data.

I observed this exposure variation last week repeatedly over thousands of images and under a variety of different settings. It's very hard to imagine that lighting is changing so quickly and consistently in an alternating way. So, I am quite sure that it is real and don't see the need to do test shots. Besides, I don't have the camera anymore as I returned it to the rental service.

JR

[Jim Michael]

OK probably academic at this point but my thought was to check the exif data to verify the camera was shootiing in manual mode and was not bracketing etc. If camera thoiught exposures were the same (i.e. exif data is constant) then would seem to clearly be some issue with the camera, not a setting. Spot meter mode can cause wide variations in exposure from shot to shot, but should not be a factor in manual mode.

[Jim Neiger]

It sounds to me like the shutter is sticking intermittantly.

[Joerg Rockenberger]

Jim, thanks for the contribution. That makes much sense. Have you seen this with any of your cameras? JR