Schneider-Kreuznach — 210mm f/5.6 convertible plasmat for 5x7 and 4x5, converts to 370mm f/12
The Symmar 210mm f/5.6 is the most common of Schneider-Kreuznach's convertible Symmars, working as a standard lens on 5x7 inch cameras and as a long-normal or portrait lens on 4x5. It predates the Symmar-S and Apo-Symmar and should not be confused with either.
Removing the front cell converts it to 370mm f/12, and both focal lengths are engraved on the barrel — the clearest way to identify a convertible Symmar in a listing. It is a six-element, four-group symmetrical plasmat, single-coated, usually in a Synchro-Compur or Copal 1 shutter, with an image circle of approximately 300mm at f/22.
At 210mm it performs solidly from f/16 down and covers 5x7 with useful movements. Converted to 370mm it loses contrast and edge definition appreciably; most users treat the long setting as an occasional convenience rather than a second lens.
Supply is plentiful and prices are among the lowest for a usable large-format lens of this size. Check both cells are the original matched pair, look for haze and separation in the cemented groups, and confirm the aperture scale being read matches the cell configuration in use.