"High Modulation" is correct; Schneider used that designation for enlarging lenses too. What distinguishes the SS-HM series is their 80-degree coverage. They correspond to the Rodenstock Apo-Sironar(-W) series, except that Rodenstock offered 150/210/300 while Schneider offered 120/150/210. In the shared focal lengths (150, 210), the Rodenstocks are much smaller and lighter. Optically, they're all fine lenses.

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