The camcorder guys figured out long ago how you can get the shallow DOF of a larger sensor system (typically full frame) on a camcorder equipped with a much smaller sensor (typically 1/2.8") by doing basically the following thing.
Mount the larger format lens so that the image gets projected on a piece of ground glass (i.e. where you would normally have film).
Film the ground glass from the other side, possibly using macro mode of the camcorder.
There are many improvements, like shaking the ground glass to reduce grain and I understand there is a whole science about choosing the right kind of ground glass etc.
The obvious advantage of this is that you get the shallow DOF. The disadvantage is that the setup looses light, you get no AF and there is some quality degradation.
There also used to be a similar idea in stills photography in the 1990s with the Nikon E series - it was a quasi full-frame camera which means it used a piece of optics called a telecompressor to use the whole FOV of 35mm lenses on a 2/3" sensor. I dunno what it did to DOF though.
I was wondering if you could use a similar setup today in stills photography. In particular what I have in mind is the paper-thin DOF you get with tele lenses on large-format systems. It is a personal thing, but I like old-fashioned portraits shot this way, as well as the ability to use a full range of camera movements.
I was wondering if you could have a setup along the following lines: A large format camera + a DSLR with a good macro lens used to capture the ground glass. The DSLR could even be APS-C, it doesn't really matter as long as you can take sharp pictures of the ground glass.
Maybe there is a way of doing this without the ground glass, i.e. with optical lenses alone?
Has anybody tried something like this (maybe with a middle format lens if large format is too cumbersome)?