Why is the 6D Viewfinder and Live View Metering Providing Different Results in LOW Light?

PGerst said:

In a brightly lit scene both the metering in the viewfinder and live view provide the exact same result. However, in low light, the differences are extraordinary.

In the examples below, I compare a 20D and a 6D. The metering system is set to exactly the same thing. All variables are kept as constant as possible. The differences are independent of things like JPG/RAW, stray light (low light so there is little to none), focal length, and mode (M,Tv,Av equivalent). By fixing the ISO and focal length, I'm providing comparisons below in the amount of exposure time to best exemplify the situation.

There are two situations:

Situation #1 - Metering differences between VF and LV

At ISO 1600, a dimly lit subject yields the following on the 6D:

Through the viewfinder metering: 1" (dark, exposed below 1/2 of the histogram)
Through Live View : 3.2" (properly exposed)

Situation #1 - Metering differences in VF varying with Lens and Camera

Conditions: Ambient light/very dim
ISO: 1600
f4.0 set for both lenses. This issue is focal length independent.

Two lenses,
A = Tamron 28-75 f/2.8
B = Canon 24-105 f/4.0

20D lens A (Tamron) = 8" Resulting photo was good
20D lens B (Canon) = 2.5" Resulting photo was good
6D lens A (Tamron) = 2.5" Resulting photo was good
6D lens B (Canon) = 1" Resulting photo was too dim. I manually pushed it to 8" and got about what I obtained in the other three instances.

Thanks,

Paul

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whumber said:

Do you have your eye to the viewfinder when conducting this test?

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