I have several R lenses on which I'have mounted the Leitax bayonet to use on my D700.
Everything else being perfect I found that for any aperture smaller than the max aperure there is a general tendency to underxepose.
I made a detailed comparison test using Nikon 50 1.4, Zeiss Planar 50 1.4, CV 58 1.4 and Leitz R 50 1.4 setting the spot metering for all of them.
At 1.4 the exposure was perfect in any case but at 2, 2.8 and 4 only the pics taken with the Summilux were uderexposed by at least one stop.
I do not know how much this can be relevant but the only difference I can see between the lenses I've used in this respect is that the camera has no information about the effective opening when the Summulux is in, while when using any of the other lenses this information is somehow available.
I will do other test with other lenses as soon as I can, but in the mean time,
is anybody having a similar experience?