Which S2a focusing helicoid? The helicoid on my S2a is obviously an early one as its only marked for 75mm and 100mm lenses. I know I need a different one for long telephoto lenses. I also know that there is another helicoid marked from 50-75-135-200. My question is will my current helicoid function with 50mm and 135mm lenses, or do I need to try to find a 50-200 helicoid?