5D Mark iii shoots darker than 550d?

[stephenpickerin]

Hi all,
I just purchased a srefurbished 5d mark iii from Canon.  I'm upgrading from a T2i (550d) so it's really a whole new animal.

It seems I have to have the iso WAY higher on the 5d than I did on the 550d.  I'm using a nifty-fifty 50mm 1.8 lens.  I'm used to shooting at iso 160 but the 5d is often at 1250 or above.

I'm new to full frame sensors so maybe this is normal (or is just normal for the 5d).  It certainly isn't noisy, but just feels odd that It has to be so high to get a good image.  If photos are helpful I can snap some today, but if this is totally normal then I won't worry about it.

Thanks!

-Stephen

[Skirball]

There were a lot of reports of this when the 5d3 first came out.  I never followed it closely, since I didn't have one,  so I can't give you the details.  But it seems like the issue was solved since I haven't seen anything of it in some time.  I think you'll find plenty of information if you do a search.  You can start with this thread, which has a factory reset solution that worked for some:

http://forums.usa.canon.com/t5/EOS/5D-Mark-III-Underexposed-images/td-p/9141

[TCampbell]

Exposure is exposure regardless of camera model.  If you were to meter a scene and the meter indicates that you could shoot at ISO 160, a/250th and f/5.6 (I"m making these values up) then you could shoot with those on ANY camera (and this includes film).  ISO is ISO, shutter speed is shutter speed, and aperture is aperutre.  

When evaluating the exposure, don't use what you see on the image review screen -- that's a very rough approximation.  You could use the histogram graph to get a better idea of exposure.  But the image review screen has an independent brightness adjustment.  If adjusted dim, a person could get the impression that an exposure was under-exposed when in reality it was fine.

You'd also want to make sure the lens is working correctly in that the aperture blades are stopping down to the correct level of light.  I have heard of cases where the aperture blades were damged or had somehow failed to operate correctly and threw the exposure -- but it was due to a lens issue and not the camera.

[Skirball]

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@TCampbell wrote:

Exposure is exposure regardless of camera model.  If you were to meter a scene and the meter indicates that you could shoot at ISO 160, a/250th and f/5.6 (I"m making these values up) then you could shoot with those on ANY camera (and this includes film).  ISO is ISO, shutter speed is shutter speed, and aperture is aperutre.  

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In theory, but not in practice.  There are no regulations or standards that camera companies have to stick to for this consistency.  In fact they're not even all that consistent between camera models.  ISO can vary quite a bit model to model.  As can the absolute aperture size of different lenses.  Add to that different metering algorithms and tone curve calculations, you can get quite a bit of difference depending on the camera and lens used.

[TCampbell]

Actually there is an ISO / ANSI standard for meter calibration and the camera companies do use them.

I find the performance from camera to camera to be extremely close if I use an incident meter to measure true light (not reflectance).  Reflectance is a bit trickier becuase every target will (unless it's a calibrated test target) is going to reflect a different amount of light.  Even a reflected target may vary from the camera's calibration.    Most gray card targets are 18% but few cameras are actually calibrated to 18%... many are a bit lower  (e.g. 15, 14, or 12%)

I have seen this issue mentioned before and I've tested it.  My 5D III is very accurate.

If someone believes they are not getting accurate metering or accurate exposures, then they might want to reset all camera settings to factory defaults and test the camera in controlled conditions.