The Beseler 23C has the ability to project horizontally. In this configuration you can enlarge any size for which you have projection space and that’s practical to process.
A 75mm lens is designed to fully cover a maximum format of 6 x 6cm. At large print size magnification, it won’t properly cover the corners of a 6 x 7cm negative. You need a lens specifically designed to cover 6 x 7cm negatives. A lens designed for a larger format than 6 x 7cm can be used but gives less magnification.
With a standard-column 23C projecting vertically, you get the following focal length and magnification combinations:
60mm (wide-angle), 12.7X
With the XL-column 23C projecting vertically, you get the following focal length and magnification combinations:
60mm (WA), 16X
To determine the approximate maximum projection size, simply multiply the dimensions of the window opening of the negative carrier by the magnification.
For example, the 80mm lens on the standard-column 23C gives 9X. If the window of a 6 x 7cm carrier is 55.4mm x 71.2mm, then the dimensions of the 9X projection are
498.6mm x 640.8mm = 19.6” x 25.2” (approximate size).