The Zeiss Luminars are the best macro lenses to use if you are interested in going higher than 1:1. They are older completely manual lenses specifically designed for use on a bellows and for greater than 1:1 magnification. Bellows are also useful in the macro world so you can do things like tilts and swings. Tilts and swings can help increase your depth of field without restoring to extremely high apertures which kills your image quality, due to diffraction. If you want to learn more about movements possible on a bellows read about the Scheimpflug principal not exactly light reading but interesting..