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EOS 5D MK3 underexposing by 1 or 2 stops - anybody else finding this?

11 Aug 2019 9:02AM
Had a Canon EOS 5D MK3 for a few months now, bought it used with really low shutter count (8K) but I'm finding about half the time the camera underexposes between 1 and 2 stops, regardless of the mode, or metering mode. If I'm in Aperture Priority, or Shutter Priority it underexposes no matter what metering mode I use, be it: evaluative, spot, centre weighted. Same in full manual mode too: I set the exposure based on the cameras metering modes.

In the studio with strobes and a flash meter it is spot on, but I'm in full manual mode and using a flash meter for readings.

Is there an in-camera setting (perhaps a factory default setting) that needs to be changed to prevent this? Anybody else finding this?

Like I said, only does it about half the time.

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sherlob Plus
13 3.0k 129 United Kingdom
11 Aug 2019 11:09AM
Forgive me for asking the blooming obvious, but you have checked that you haven't got exposure compensation set? This can be applied to all modes if I recall correctly.
11 Aug 2019 11:28AM
Yes, first thing I checked. But, you're right, it seems to be like exposure compensation is set to 1 or 2 stops under, but it isn't.
Chris_L 5 5.1k United Kingdom
11 Aug 2019 11:54AM
Putting it on your tripod and pointing it at some kind of neutral reference scene put camera in AV mode and set aperture to f8 and note the shutter speed suggested when half-pressing your shutter button.

Then switch to M, stick with f8 and note the shutter speed that you need to choose to get the meter to read bang in the middle. Is bang in the middle producing an underexposed picture?

What are the two shutter speeds?

11 Aug 2019 12:22PM
Thanks Chris, I'll check this later and post back
11 Aug 2019 4:54PM
Ok, Chris. Following your instructions in AP at F8 shutter speed is 0.6 seconds and in manual, to get pointer to centre (correct exposure) it is 13th of a second. In manual mode I have to dial it 3 stops over-exposed to get 0.6 seconds. This does not make sense.
11 Aug 2019 4:56PM
On from above, should the shutter speed be the same in both AP and Manual?
11 Aug 2019 5:00PM
On from above, I did not actually take two photos to check the results, perhaps I should have done that?
Chris_L 5 5.1k United Kingdom
11 Aug 2019 5:20PM
If the meter is dead centre in manual and the picture is underexposed then that suggests a metering problem. If it's correctly exposed in Manual mode (when meter is centre) that suggests something else if up especially if camera chooses a shutter speed that underexposes, a speed that you would not choose when exposing manually.

Check that FEC (Flash Exposure Compensation) and flash settings are set to normal. in certain circumstances they might alter overall exposure.

The shutter speed should be the same in both (unless the light has changed). Also check that auto ISO is not set.
Dave_Canon 13 1.5k United Kingdom
11 Aug 2019 7:42PM
Chris may be on to something but, if all else fails, you might try the "factory reset" which would ensure there are no odd settings. Of course it would be as well to note any special settings you have before resetting.

12 Aug 2019 11:37AM
Chris, where is the FEC in the settings menu, can't find it?
Philh04 Plus
13 2.0k United Kingdom
12 Aug 2019 11:58AM
FEC can be accessed direct via the button in front of the LCD, it is the one with a dimple... But FEC is unlikely to make a difference to ambient exposures.

Just a further check, is the metering mode (evaluative, spot etc) the same in aperture priority and manual?
Chris_L 5 5.1k United Kingdom
12 Aug 2019 1:12PM
Check whether safety shift is turned on or off and ensure that you are not shooting in an exposure bracketing mode.

There are so many things to check that It really is worth performing a full factory reset if you have not already done that.

There's a wealth of custom functions ( for example ) which the previous owner may have tweaked that might manifest themselves as odd behaviour to a new owner.

17 Aug 2019 9:54AM
Ok, final update on this. Yes, I use the black rubber eye cover on tripod.

Anyway, I bought an 18% grey card and stuck it on my wall and put camera on tripod, filled frame, put rubber eye cup cover in place and took a reading in Aperture Priority. I then went in to full Manual mode and chose the same shutter speed and aperture that resulted in my Aperture Priority reading and the little exposure meter digital needle was bang in the middle, so both exactly the same, as I'd expect them to be.

When I then zoom out and point the camera to a different scene in the room, still the same wall and falling under the same light as the grey card, only now my kitchen table (which is pine wood and much lighter than 18% grey) with some items on it, the Aperture Priority mode now chooses a faster shutter speed, by about two stops, resulting in underexposure. If I then go back into Manual and use the same settings that were read off the grey card and re-take the image, it is perfectly exposed with a nicely balanced reading on the Histogram.

The result of my findings is that all the metering modes on the camera: Evaluative, centre weighted, spot, etc, all underexpose by 2 stops on average for most of the scenes I shoot, landscape, portrait, buildings, anything outdoors. The only time I get a perfect exposure is doing studio strobe work with a flash meter.

While doing this grey card test I also took two readings with my Sekonic L-308X meter in both incident and reflected modes and it came back with the same as the Canon, F4 with a shutter speed of 1/4th second at 100 ISO, which tells me all is good.

I've deduced that I can only really use 'spot metering' with this camera and that I must aim the spot at something that is as close to 18% grey as possible and even then to check the histogram to make sure it is balanced and not all leaning too far to the left.

Anyway, appears there is no fault, just the 5D MK3 is really fussy and there is no room for anything outside 18% grey as far as the cameras built in exposure sensor is concerned. But then again, built-in exposure meters that take 'reflective' light readings are never going to be spot on, but the Canon just seems to be very unforgiving, unlike my old Nikon D3s, which did a much better job.

So, to re-cap, I just have to use spot metering and aim for subjects in the scene that look close to 18% grey and then hit the exposure lock button on the back of the camera, re-compose, take shot and check histogram.
Chris_L 5 5.1k United Kingdom
17 Aug 2019 12:27PM
Why not set exposure comp to +1 or +2 permanently?

Auto exposure is always a bit of a fudge compared to eyes and brain. Cameras over expose darkness, under expose the snow etc. Even with spot metering shooting into the sun the photograph will be different from your eyes.

Never known a camera underexpose so much so regularly and repeatedly with general scenes like the one you describe. The 5D has long been a favourite of wedding photographers and perhaps by the time the Mk III came out engineers had one eye on white bridal gowns and retention of highlight detail.

Your testing method seems sound. But, did you take the advice to do a Factory Reset. I think that is vital for piece of mind.

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