ic- you're looking at the 4550XLG (7452L outside the U.S.). For the 4500II (7451 outside the U.S.), the baseboard is 60x60. Magnification is 17.5X.

My earlier 16x20 baseboard came from the Adorama site. I think kbh is probably more accurate. Should be able to get a 20x24, though...