I found the sensor I had could see through paper, but not through paper with black ink on it. So, I just printed it out, cut the circle and mounted it.
Yah that works too. I have found that I can do it this way SUPER accurate. and it cuts it out for me. Cant beat that. But paper works too. I am hoping this will hold up for the long run.
True, the paper ones tended to get bent out of shape when I was working on other stuff that was nearby. I printed a whole page of them so I had fresh ones ready to go.