The subject of fitting a focal reducer optic to the 4K URSA has surfaced fro time to time. Recently on reduser, there was a post regarding fitting a focal reducer optic within the throat of the DSMC2 style of camera. The results were encouraging.
So prompted and having recently had a big URSA PL turret partially apart in order to design and fit a custom Nikon F-Mount, I also examined the possibility of fitment of the Metabones "Ultra" 0.71 optical cell within the throat of the big URSA camera.
It seems that it is a workable possibility. The flange face of a particular mount is set back about 4.2mm when this optical cell is in the image path.
It is unlikely that PL-Mount cinema lenses can be accommodated. The deep shoulder of the lens mount takes up space. Many of the lenses have rear elements protruding significantly rearwards, which means that many will clash with the front element of the "Ultra" optical cell.
My tests thus far attempting to offer up Cooke Speed Panchros, a Kinoptik Tegea 9.8mm and a Cine Xenon 28mm to the Speedbooster arrangement demonstrates that their rear structures are too far rearwards and clash with the front element of the Ultra optical cell.
The Rokinon Zeen and Zeiss CP2 series of lenses seem likely to work so long as their rear barrel structure is no wider than the opening in the front of the URSA camera body with the intermediate adaptor removed.
Comparitive image pairs with and without the speedbooster element in place can be seen here. The Speedbooster optical cell and 20mm f1.8 Sigma-for-Nikon lens were placed with a primitive jig arrangement for the rough test.
Edited by Robert Hart, 16 July 2017 - 05:13 AM.