I just got a new G. A. S. stresser from ebay. It is an f/4.5 6 1/2" (by the math, J's rigatoni method proved about 13") Bausch and Lomb barrel lens, the pic is here. The filter threads (front and back) are 62mm. Two elements with aperture range from 4.5-32. Retaining ring thread is about 67mm and the ring flange OD is about 80-81mm. There are five equidistant countersunk mounting holes around the face of the flange. What shutter would my G. A. S. need in order to be satiated?