I recently purchased an older Schneider Convertable Symmar lens. It is marked 1 80/5.6 and 315/12. According the the serial number, it was made about 1971 and is all black.
The salesman told me to remove the rear component to use the lens at 315. Anoth er question on this site also references removing the rear component. However, when I called Schneider to get a replacement index screw to engage the slot in m y board (the original was missing and Schneider customer service was super!), I asked about the "conversion". They said to remove the front component, as does Ansel Adams in his book "The Camera".
So I tried both ways. With the rear removed I get an infinity focus at about 10 .5" between the standards (a bit short of 315mm), and with the front removed I c an't get anything to focus. That would appear to agree with the "remove the rea r" recommendation. The complete lens focuses at infinity with about 7" between the standards (seems to agree with 180mm). Removing the rear component does req uire more effort, but it keeps the shutter protected from the elements and retai ns the filter ring---so I actually prefer that arrangement.
What's the correct method to convert a Symmar, and why do some sources say to re move the front component and others the rear? Were these lenses made in two dif ferent configurations?