These are extreme macros meant for use with bellows (obvious because of the absence of a focusing helicoid)....kind of like the Macro Nikkors and the Zeiss Luminars........the magnification is controlled by the bellows extension, but typically these lenses are optimized for a particular magnification. 10:1 would be difficult to use in the field of course.
Originally Posted by StoneNYC
Canon's MP-E 65 is a "zoom" macro.....goes from 1-5X (meaning 5:1 life-size).....supposed to be a fantastic lens. I am, however, wedded to the Nikon system and besides, I have the coveted Zeiss Luminar 63mm anyways.