Metering mode was matrix. The camera was not moved, the light source was constant, focus point was not moved. Light source was a mix of indoor lighting and light from 2 nearby windows. All I did was change the f stops on the camera.
This afternoon I went outside and took hand-held pictures of an almost blue sky. ISO was lowered to 100, but the same f stops described above were used. There was a drop off in brightness going from f/2.8 to f/1.8, but not as much as that seen with the indoor shots.
I repeated this outdoor shooting by taking pictures of a lush hemlock bush...again, there was brightness fall-off between f/2.8 and f/1.8 that was somewhat more pronounced than that seen with the blue sky.