The two cameras have the same 3:2 sensor aspect ratio, except that the Leica S2 has a sensor that is 25% larger linearly (56% larger in area). However, the Nikon D800 has another 2 years of sensor technology advances in its favor.
With better lenses and a larger sensor with larger photosites, we might expect the S2 to easily win the contest, at least at lower ISO values. But that is not a given with top-notch lenses on the D800, and what happens at ISO 400 on up?
The following comparison would be appropriate:
- Nikon D800E + Zeiss ZF.2 100mm f/2 Makro-Planar or the Leica 100mm f/2.8 APO-Macro-Elmarit-R (the Zeiss has a flatter field, so it might be a better choice).
- Leica S2 + 120mm f/2.5 APO-Macro-Summarit-S.
Alternately for a wide angle comparison:
- Nikon D800E + Nikon 24mm f/1.4G or Zeiss ZF.2 25/2 Distagon.
- Leica S2 + 30mm f/2.8 Elmarit-S ASPH.