It is not so simple. The prism introduces spherical aberration which no "setting up" can undo. However, this effect is negligible past about f/2. The prism can also introduce astigmatism if the lens' exit pupil is not a healthy distance, like 30 mm away from it. With astigmatism, the image corners will be unsharp even with considerably more stopping down. Thus for successful use of a non-RX lens on a RX camera verify by eye that the exit pupil (which is the apparent location of the iris when seen through the rear elements) is deep in the lens. Notice that these considerations have nothing to do with focal length. The old RX-rules about less than 50 mm and greater than 50 mm were wrong.
