Originally posted by Paul Ewins I don't think Schneider were ever happy with "convertible" lenses because there is a compromise in image quality when you use one half of the lens. I'm guessing that it was a popular selling point in the US so they went along with it for marketing purposes. The Symmar-s is also convertible, but when they tweaked it for optimum sharpness as a whole the performance of the individual cells was reduced so the "convertible" markings were dropped. Technically the plain Angulons are convertible too (as shown in the attached page from the 1934 brochure) although that wasn't mentioned much in later years
Interesting!
Well I took 4 test shots today, I used the same scene, same exposure settings.
I used the 100/175, shot it, then i swapped the front cell for the 135. I had thought I would get a wider angle, but no. I got a slightly longer lens. Maybe a 115mm
Then I installed the 135/235, again, same scene, same settings. Then i swapped in the front cell for the 100. And in fact I did get a wider lens, again about 120 mm.
In any case, the swapping cells to get more focal lengths is not worth the trouble. If I had gotten a wider than 100mm by swapping cells, then I would have been ecstatic. In both cases when i swapped the front cell, i got a middle focal length.
The 100/175 was meant for a 6x9 film size, and I can see some vignetting at large aperture. It is not very obtrusive, and the 175 does not vignette at all, so I think this will be my general use lens.