I only know of a few six-element 75mm lenses. Koumaron, and two Fiujinons. To know for sure if you have coverage for a 20x24 it would be wise to invest in a Peak-1 magnifier. If you don't have that magnifier, you can make little prints of the 4 corners and center of a 20x24 projection and compare them. You won't need 20x24 trays or paper to do that.