Postby andrewch59 » 15 Nov 2017, 11:56
Ray, stand in a dark room, with window or door that receives light, point the rear of the lens toward the light coming through the window. Hold a piece of plain paper up to the front of the lens and when an image appears sharp on the paper, measure the distance between the paper and the waterhouse slot or iris (axis). Ensure that you have the focus on something outside in the distance(infinity)