Canon 5D3 & variable neutral density filter results in underexposure

[vartkes]

Am I going crazy?
I bought a 5D3 recently and tried to use my Singh Ray vari-density filter with it. This filter functioned fine with my 5D for years! Here is what is happening:
two to three stop underexposure when using the filter when set to >4 EV filtering!. Shooting parameters are Aperture-priority, mirror-up, evaluative metering, f11, multiple prime and zoom lenses (all Canon L) produce the same result. Here is the kicker to the mystery >> when camera is in live-view mode the exposure is CORRECT !!! if not it goes back to under-exposure. What is the difference between 5D and 5D3 that can cause this absurd behaviour?
Thanks for any insights or sharing similar experience; I do want to assure myself that I am not simple!
thanks, Vartkes

[theguywitha645d]

Light is leaking through your viewfinder. I bet if you cover your viewfinder, your exposure will be correct.

[ErikKaffehr]

Light from viewfinder messing up measurement? DSLRs often have a shutter for viewfinder ocular, have yo tried that?

Best regards
Erik

Am I going crazy?
I bought a 5D3 recently and tried to use my Singh Ray vari-density filter with it. This filter functioned fine with my 5D for years! Here is what is happening:
two to three stop underexposure when using the filter when set to >4 EV filtering!. Shooting parameters are Aperture-priority, mirror-up, evaluative metering, f11, multiple prime and zoom lenses (all Canon L) produce the same result. Here is the kicker to the mystery >> when camera is in live-view mode the exposure is CORRECT !!! if not it goes back to under-exposure. What is the difference between 5D and 5D3 that can cause this absurd behaviour?
Thanks for any insights or sharing similar experience; I do want to assure myself that I am not simple!
thanks, Vartkes

[vartkes]

Ah yes this makes sense; light leaking through the viewfinder for 2+ seconds will shorten the exposure. I will test this next time I am out on a sunny day! Thank you