The widest lens Rollei offered for the SL35 line outside the Zeiss Distagon, they do not come up often. Rollei announced the Rolleinar-MC 21 mm f/4 in January 1977 for the SL35 M, SL35 ME and SL35 E, and it was made in Japan by Mamiya; optically it is the same nine-element, eight-group design Mamiya sold as the Auto Mamiya-Sekor SX 21 mm f/4, and Rollei also sold it under the Voigtländer name as the Color-Skoparex AR 21 mm. It gives a 90 degree diagonal angle of view on 35 mm, focuses down to 0.45 m by its own scale, and takes 58 mm filters behind a fixed scalloped shade. Serial number 7901322. The barrel is in good order: usual signs of use best described through the photo's in this listing. The bayonet flange shows light silvering from mounting and a small rough spot on the inner baffle ring beside the coupling pin. The front element is clean and the multicoating shows its green and amber reflections without wipe marks. One point needs stating plainly. Held against the light (DSC01846), a thin dark crescent with a flaked edge is visible at the extreme lower rim of the optical path. We read this as blackening paint lifting from the edge of an internal element, or the onset of edge separation. It sits at the very periphery of the clear aperture and would not normally show in a photograph, but it is there and the estimate takes it into account. The rear of the front element shows trace signs of what could be either cleaning marks, slivers of barrelpaint such as 'Schneideritus' or early onset of fungus. Inspection of the optical path with light shun through the length shows minor dust spots but no haze or visible trace of fungus. The aperture works well and reacts promptly. The focusing helicoid is relatively smooth, with some resistance. Included In the lot: Lens only. No caps, hood or case.