For RED owners who went ahead and fitted the P+S Technik IMS mount system and want to shoot 2K with a B4-mount lens P+S are auctioning their optical viewfinder for B4-Mount lenses at a bargain basement price, compared to what they originally were charging.
They have two remaining at this web address. It is all in German so you will need to use Google Translate or suchlike to make sense of it all.
My understanding of the optical viewfinder is that it was originally engineered for the SI2K camera system. They initially made a B4-mount with an optical block to correct lenses made for 3 x sensor prism systems for correct optical presentation to single 2/3" sensors. The viewfinder is an extention of this design in that an optical split is taken from the optical block stage of the B4-Mount. The image from this lands on a groundglass which is marked for 2/3" inch sensors.
At one point P+S proposed making a 35mm PL version for their X35 but I have not heard if this is still being progressed.
Given the apparent closer couple of the front plate to the sensor on the EPIC/SCARLET and the apparent extra workroom between the front of the camera body and face of the PL-Mount system, the new RED camera family cries out for an optical finder for the purists out there who still like to see their lens image on a groundglass.