The column height is a significant factor in how big an enlargement you can make. The taller the column, the greater the potential magnification. You should be able to print up to 20x24 with this using the (home-brew replacement) baseboard. If you wall-mount it and project onto the floor, you can probably go quite a bit bigger than that. The 4x5 designation has to do with the maximum negative size, not maximum print size.