Today, I setup a grey card on a wall and took a series of shots, using a tripod, and a Canon 5d, gradually over exposing and under exposing the greycard.
Here is the file that is exposed according to the meter. I will call this MIE, [Meter Indicated Exposure].
Here is the 2nd shot which is one stop over exposed. I will call this MIE +1.
Here is the 3rd shot two stops over-exposed, I will call this MIE +2
Clearly, given that MIE has the histogram to the left of centre and no RGB values anywhere near 127, I'm guessing that this CCD is NOT recording things correctly. Given that MIE+2 gives me a histogram that appears correct and a set of values closer to 127, I'm going to assume that, this camera, a brand new Canon 5d is under exposing by 1/2 to 1/3 a stop, the next file is far to bright and the histogram is way to far over to the right for it to even come close in this test.
There are several other issues that are bothering me about the results of this test, the vignetting, mainly, so much so I am going to attempt this again under more controlled conditions.
At one level this test is inconclusive, why is the CCD not recording an even set of values for example? So, I'm asking both my readers to stay tuned.
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The vignetting is a known issue with the 5D and a lot of other full frame cameras, due to the filter mask on the front of the sensor having 'vertical' microlenses, you get light falloff towards the edges in a lot of circumstances. Some lenses contribute to it as well. Leica have tried to deal with it in their M8 by having the microlenses angled slightly as you get nearer the edge of the sensor (http://www.dpreview.com/reviews/leicam8/), and it's one of the reasons that Nikon originally claimed was stopping them doing a full frame camera as nobody had solved the issue yet. Although Nikon is now releasing a full frame camera, so who knows :)
As for the exposure problem, dunno, but one of the guys I used to shoot with back in the 90's used to always complain about Canon metering and each Canon he had had a -1/3, +1/2, etc engraved in the back as he'd worked out the amount of exposure compensation he needed for each to get it right :)
or, just looked at the title of the screenshot - 5D??
sorry s2, at the start you mention its a 5D, then at the end that it's a G5. since you don't mention a lens, i figure you mean a G5???
am staying tuned...