This guest post on using the Nikon D800 as a negative holder for a large format camera + lens setup is by Jan Håkan Dahlström:
It’s really quite simple. What you need is a large format camera, a suitable lens and a digital camera body instead of a film holder. In this case it’s an Arca Swiss 4x5/9x12 rail camera, an Yamasaki Congo 180 mm/4.5 lens and a Nikon D800:
First, you’ll need to mount the D800 on the camera. I used a lens board with an opening about the size of the body opening of the D800. On the lens board I mounted a Nikon mount extension tube. The tube must be at least 15 mm, otherwise the prism of the Nikon body will hit the lens board. Preferably it shouldn’t be thicker than 15mm since the thicker the extension tube, the taller the lens you’ll need to use due to lens-focus plane distance.
All lenses over approx. 135mm can be used but a large format lens is to be preferred due to its wide image circle. Using a large format lens increases the possibilities to swing, tilt and rise the standards of the camera.
Once this is done, you can start shooting, preferably in the Live View mode. Procedures are now a blend of traditional large format photography and D800 high end digtal shooting.
Two sample images taken with that setup: