I just cut down a full page magnifier from Staples to use on my Reflex-Primar 9x12 SLR. It brightens up the screen, but it's a little coarse. It's an improvement, but it doesn't "snap" the focus. It would be nice to find something finer, but for $7--it's an inexpensive upgrade. I used a fine-toothed Exacto saw to cut 1/2 way through the fresnel and then snapped the cuts over a table edge.