It's funny how often an important variant of the RTS is overlooked; I'm referring to the RTS Fundus.
This had 2 incarnations: the usual with a raised rim for the electronic shutter release plus the lock button on the front of the top plate for the film speed dial, and then the additional (and much more costly) type that also had the heavily damped mirror assembly.
The photo of the 2 RTS types shows the external differences - I've also attached a piccie of the RTS Fundus with a rare Polaroid back which was much more versatile to use than the Preview.
I have bought many of these RTS variants and still use them with the 250 back + PMD/W6 for laboratory work.
