Focusing E-Mount For Ultrafast Lenses

myminifactory

There are a variety of old ultrafast lenses cheaply available. These lenses, usually marked between f/0.75 and f/1.6, typically have no aperture iris, no focus mechanism, and a giant external screw thread intended for mounting. They generally can't focus to infinity even on a mirrorless body, and IQ is scary soft, but sometimes that's a feature.... Anyway, I originally mounted these lenses by gluing an M42-to-A-mount adapter on the back (as I described in my Instructable, http://www.instructables.com/id/Using-Ultra-Fast-Lenses-on-DSLR-Cameras/ ). Instead, I've now built 3D-printable focusing E-mount adapters where the lens screws in using the large external thread (see 2nd photo) and can be focused by partial unscrewing. One mount has a 60mm thread that works with my Kowa 55mm f/1 and 42mm f/0.75; the other has an 80mm thread that works with my XR-Heligon 95mm f/1.3. The E-mount flange is a new design that should fit both older Sony E-mount bodies and the newer all-metal E-mounts (they have been tested with NEX-5 and A7II). In fact, the flange on the 80mm adapter has a different internal profile from the 60mm one, because the rear element of the XR-Heligon is huge and a standard-thickness E-mount could vignette. The last couple of photos were taken using the purple PLA adapters on an A7II and NEX-5. The kiwi was using the Rodenstock XR-Heligon and the princess ornament was using one of the Kowas. Note that the large flat on the adapters makes it difficult (but not impossible) to access the E-mount body lens release button and the 80mm adapter just barely clears the grip on my NEX-5, but the only way to avoid these issues would be to mount the lens farther away from the sensor, which would limit the focus range. The adapters print with the E-mount side up. This means there is a huge unsupported flat under the E-mount flange -- and that needs supports when printing. Both cura and slic3r had issues making good support structures, so I have designed-in a support that should simply be broken out of the center of the adapter after printing.