In the opening post, @Rosssiiii says he is using a Durst Neonon 50mm enlarger lens and bellows.
To fill an APS-C sensor with the image of a 35mm negative or slide requires the negative be magnified about 0.65x, so less than 1:1.
The problem I had trying to use the formulas was locating the lens node. Not marked on most lenses, so any measurement requires some guesswork. In some cases, if the calculations are only a few millimeters off, it can make the difference between whether a particular combination will work as intended, or not.
To fill an APS-C sensor with the image of a 35mm negative or slide requires the negative be magnified about 0.65x, so less than 1:1.
The problem I had trying to use the formulas was locating the lens node. Not marked on most lenses, so any measurement requires some guesswork. In some cases, if the calculations are only a few millimeters off, it can make the difference between whether a particular combination will work as intended, or not.