I need to photograph about 50 large original paintings on canvas. My standard wood easel works fine for up to 36" x 48" canvas. But for larger pieces (6' x 7'), I need a much larger adjustable easel. So, I built one from a design I found on the web on THIS site. The design calls for a series of holes drill on the front of the two rails. Round dowels are used to hold the easel shelf. I am looking for new ideas. I would like the easel shelf to slide up and down and be held in place by a mechanism that holds the shelf in place by putting pressure on each of the two rails. A crude method would be to use a large spring clamp on each rail and lay the shelf on the clamps. Any brilliant ideas?