Focusing E-Mount For Ultrafast Lenses
by profhankd, published
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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.
Break-out the internal support
It should be pretty each to remove -- I twisted it out with pliers.
Work the screw threads
The screw threads should print directly usable, but it may be helpful to work it back and forth a bit to clean-up any of the usual 3D-printing strings, etc. You might even need to file-off a drip or two on the threads or the flat inside of the adapter. I recommend working the threads a bit to test fit, filing a little if needed, and then using water to clean off the plastic dust.
Paint inside black
I usually use opaque black filament for adapters, but here I used dark purple. To ensure no light leaks, I painted the inside of the E-mount flange and the inside back of the E-mount flange with flat black latex paint. This isn't really needed, but the paint fills any pinholes nicely and it can't hurt. You don't need to paint the screw thread, etc.
Paint the alignment dot
There is an alignment dot on the outside for aligning the adapter with the E-mount on the body for mounting. I put a dot of white paint in the cylindrical cavity printed for that purpose. It's the white dot visible in the 3rd photo. I use white because Sony uses white for the corresponding mark on the body.
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Focusing E-Mount For Ultrafast Lenses by profhankd is licensed under the Creative Commons - Attribution license.
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