6D Random underexposed image

[Z0mbieRecruiter]

Hello. I hope you can help.  I own a Canon 6D and twice in the past week I was taking photos where a random image would come up underexposed.  I was shooting in manual mode, each image was identical other than a slightly different angle and shot only a few seconds from each other.  Looking back at the settings for each image, the settings are exactly the same (ISO 1600 F/5.6 1/60 sec).  While taking the photo, the image in my view finder also darkened.  Both times this happened using the same lens, so I suppose it is possibly a lens issue?

Thanks in advance!

[MichiganPhoto]

As stated in OP.  Precisely same settings on both successive images.  Very random in nature.  I've only noted it in the VF and not in LV.

Can occur with multiple lenses.  So, it's not aperture, unless the camera is stopping it down for some reason.  If the camera is stopping it down, it is not reflecting this in the EXIF.  By all metrics, identical settings and can happen w/in seconds of each other so, it's not a drastic change in ambient light. 

This problem occurs irrespective of whether or not the aperture is stopped down or wide open.  But, I typically shoot wide open unless I have a need for stopping down.

I do not recall it happening in live view.  But, the live view experience in the old 6D is abysmal so LV doesn't get used unless on a long exposure with a tripod.  To whit... I have not noticed this occur on such occasions.

I'm really hoping to find someone who has actually solved this issue, but I thank you for your time.

[Peter]

As I wrote, take a look at the front to see if the aperture moves when it shouldn't. I don't really know what else could be the culprit...a slow shutter curtain, but that should give other symptoms also.

Firmware 1.1.8 solved irregular exposure, but only in Live view and with some TS-E lenses.

Any raw samples with the same settings and different brightness?

[Z0mbieRecruiter]

Just adding updates as the original poster. After trying updates, I broke down and got the lens repaired /cleaned. The tech didn't see anything as an issue, put it back together and problem stayed. Took it apart and cleaned again, worked w Sigma and it just started working again. I still use as my main lens and have only had the problem happen one more time a few months ago after 5 years of use.