# Canon 6D and old Sigma 400mm F5.6 overexposure



## pato (May 28, 2014)

Hello all
I have an interesting problem with my Sigma 400mm APO HSR F5.6 lens and my 6D. I had this lens already with a Canon 550D where it performed lovely.
Now on the 6D (or after I used it in a very humid place), it always overexposures the pictures by 1 2/3 - 2 stops. The funny part is, the camera shows it's "correctly" exposed in normal and liveview mode, but the image is clearly much to bright. I could work around it by using AV/TV and underexpose all images by nearly 2 full stops. I didn't use the lens for some weeks and then used it again, but same results (in case it was really something with the humidity).
I don't anymore have my 550D, so I can't test if the lens is broken or if it's something special with the 6D. 
What I wonder though, shouldn't it be the camera that is metering the light (based on histogram or whatever) and not the lens? If I check the picture after it's made (without compensation) it's clearly to bright in the histogram.
All other lenses that I have work fine.

I believe I once posted this question already, but I couldn't anymore find it.

Thanks
pato


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## Valvebounce (May 28, 2014)

Hi Pato. 
The camera might have exposure correction turned on for the live view, if you set up a shot, dial in a small aperture, say f11-16 then press the DOF button while looking through the viewfinder does the lens stop down visibly? If not then the humidity may have done for your lens circuitry! If it does then I'm stumped. 
Hope this helps work towards a solution.

Cheers Graham. 



pato said:


> Hello all
> I have an interesting problem with my Sigma 400mm APO HSR F5.6 lens and my 6D. I had this lens already with a Canon 550D where it performed lovely.
> Now on the 6D (or after I used it in a very humid place), it always overexposures the pictures by 1 2/3 - 2 stops. The funny part is, the camera shows it's "correctly" exposed in normal and liveview mode, but the image is clearly much to bright. I could work around it by using AV/TV and underexpose all images by nearly 2 full stops. I didn't use the lens for some weeks and then used it again, but same results (in case it was really something with the humidity).
> I don't anymore have my 550D, so I can't test if the lens is broken or if it's something special with the 6D.
> ...


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## pato (May 28, 2014)

This lens can't be stopped down thanks to it's age/Sigmas protocol hack/Canons update to protocol. I can only shoot full open (which is fine for my subjects).


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## TexPhoto (May 28, 2014)

I had this problem with a 15mm fisheye. Never found solution. Older Sigmas are just known for not working correctly with Newer Canon equipment.


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