60D Live View exposure anomaly

Just yesterday I noticed that stills taken with Live View were coming out around 1-2 stops darker than those taken using the usual, optical viewfinder with high shutter speeds (1/3200s or faster). This isn't a metering issue: I had the camera in full manual mode -- same shutter, aperture and fixed ISO, only the Live View ones came out darker.

My first feeling was that this could be impending shutter failure, but if that were the case I'd expect to see the underexposure with shots taken using the optical viewfinder too. But those have all turned out spot-on. This strange behaviour was quite consistent -- underexposed only when taken using Live View at faster shutter speeds. I also tried with the camera in high-speed continuous shooting mode, and got the same difference in exposure.

There is some evidence, looking at the depth-of-field in some of the darker shots, that the camera was taking it upon itself to stop down a bit (although that isn't certain). Can't see any marked differences in noise, so I don't think it's a random change of ISO.

This happened with all my lenses. Oddly, this first started after I acquired a Sigma 17-50 f/2.8 OS lens, although this may be coincidence. I decoupled the lens, removed the battery, and left the camera overnight. It's now back to normal. The only thing I can think of is that something got seriously confused in the camera's software and is now reset.

Anyone else seen anything like this?

What i know is that when a camera is in live view it will adjust the aperture to save your sensor from being fried by ambient light whereas normal viewfinder viewing is always wide open aperture. So somewhere along the line your camera must have been getting confused. Were you outdoors when it happened? Well if you said it went away after resetting the camera, i wouldnt worry too much unless the problem regularly repeats its self. Weird things often happen to cameras.

Did you cover the viewfinder in live view with the eyepiece cover? I think I remember reading the viewfinder has to be covered to prevent confusing the sensor.

If you followed the instruction its that black rubber gadget you mounted on the neck strap. Page 124 of the manual.

kenshap wrote in post #16082000
Did you cover the viewfinder in live view with the eyepiece cover? I think I remember reading the viewfinder has to be covered to prevent confusing the sensor.

John from PA wrote in post #16082168
If you followed the instruction its that black rubber gadget you mounted on the neck strap. Page 124 of the manual.

As an aside, live view does not require the viewfinder to be covered. Exposure is set using only evaluative metering on the sensor itself. When using the viewfinder, exposure is read from the focusing screen. That's when extraneous light entering the viewfinder can affect exposure.

kenshap wrote in post #16082000
Did you cover the viewfinder in live view with the eyepiece cover? I think I remember reading the viewfinder has to be covered to prevent confusing the sensor.

That shouldn't make any difference when in 'M' mode. No form of camera metering is being used to control the exposure.

Examples with full exif?

hollis_f wrote in post #16083136
Examples with full exif?

It's behaving normally at the moment, and I scrubbed all the old ones. Will post as soon as this happens again and I can take controlled shots... there may well be something interesting lurking in the EXIF. All I can add right now is that it'll be two shots of the same scene, with the same light and exactly the same shooting settings -- but the Live View one will be darker.

[Comment about slightly uneven exposure in Live View removed: had Silent Shooting on, known phenomenon...]