There have been many generations of Schneider Symmars. The first was an f/6.8 design, similar to a Goerz Dagor. That lens series was made before and after WWII; later ones are coated with a red triangle on the nameplate ring. Not common now, and usually seen as 210mm.
That design was replaced in the early 1950s by what is known as the "convertible Symmar", with a second f.l. mentioned on the nameplate ring and a second set of f/stop markings (in green), for example the 180/315. These lenses were meant to have the *front* group removed to use the converted focal length. I tried that lens first with the rear element removed and was disappointed with the performance, not knowing any better. Using only the rear element for the longer f.l. worked better, and someone 'in the know' told me that the converted f.l. was meant for portraiture... although I never used it for that.
This series of lenses was replaced by the Symmar-S lens series c.1972; in the introductory brochure, Schneider mentioned that they had discontinued the convertible feature to give better performance with the whole lens. That very popular series was multicoated in the mid-70s, and replaced by the Apo-Symmar c.1990; again no mention of convertibility, and the same was true of the Apo-Symmar L line that followed.
Which is not to say that you can't remove a front or rear group from any of these newer models to convert them to a longer focal length; just that you'll have to figure out your own f/stops, and that you will have to decide if the converted image quality meets your needs.
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