That 58/1.8 is a seriously sharp lens. The mount is physically interchangeable with the Exakta mount, but IIRC you don't get auto-aperture on Exakta lenses---you have to stop them down manually, or you can do what everyone else does, forget to stop them down at all and overexpose by 37 stops. :-) In all seriousness, there are a lot of interesting and cheap lenses for the Exakta mount out there, and a Topcon makes a nice platform for experimenting with them.