I currently have a 38-60 shade that fits my 50mm FLE but it is worn and doesn't stay firmly attached to the lens. I also have a spare 100-250 shade that is in excellent condition in that regard. I always felt the 38-60 shade is a bit shallow to provide much protection for the 50 lens and since it works with the 38 I suspect this shade could be a bit longer. If I were to trim the 100-250 down for the 50 could I go a bit longer without vignetting. I am not sure how to calculate the length other than trial and error. Has anyone else done this before and have a length you could suggest? Thanks for any advice.