This is for real. A Nikon D800 mounted on the back of a 4x5 camera:
partial quote from the article:
"Itís 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 itís an Arca Swiss 4x5/9x12 rail camera, an Yamasaki Congo 180 mm/4.5 lens and a Nikon D800:"
Worth a look. Actually looks kinda fun