After hearing about Arri Signature Primes adding diopters to the back of the lens to give a vintage lens look I got thinking about how if you unscrew the back PL mount flange element on a Sigma Cine Prime it looks like a lens filter screw. Did some measurements and its 50mm and found a not very common step down adapter ring from 50mm to 49mm on ebay. It works! I can now add any 49mm filter onto the back of my sigma primes.  The adapter from 50mm to 49mm is actually necessary to add little s