Hmm. I wonder how the length of the S-50 compares to the hood I have. It's labeled "Series VII Canon Lens 50mm F:1.5"
Now this hood came attached to an 85/1.9. It fits on a 50mm outer-diameter lens, not a 42mm one, which means it actually won't fit on the labeled 50/1.5 (which uses 40mm threads, 42mm outer diameter). However, it seems to be a perfect fit for the 50/1.4. Why is it labeled 50/1.5 then?
Scott