Mamiya Sekor-compatible M42 Lens To Sony E/FE Body Adapter

The M42 “universal screw thread” mount for camera lenses was, and remains, very popular despite the fact that no camera bodies natively accept M42 lenses. Although there are many adapters available, there are several variations that require slightly different adapters. The most challenging is the Mamia Sekor SX lens series (the 135mm f/2.8 is shown in the 3rd photo), which uses M42, but extends the aperture ring back over the M42 front plate – which doesn't work with most adapters because they have a larger faceplate diameter, but works fine with these 3D printable adapters. Beyond that, there is the issue that some M42 lenses require that an auto-aperture pin be depressed in order for the aperture blades to respond to the aperture ring setting; this can be solved a variety of ways, but incorpoating a ledge in the adapter to depress the pin is common. On the other hand, such a ledge interferes with some M42 lenses that don't need the pin depressed. There also can be minor corner vignetting with 3D-printed adapters to E/FE mount because the thickness of the adapter's E/FE mount reduces the clear diameter a bit more than typical metal mounts do.

The result is that there are a bunch of versions here. The files are named by the version date, but also have a suffix after ‘_’ that says what they contain. The meaning of those codes are:

• p: Plain version for single-color printing
• pv: Plain version with extra thin E/FE mount to minimize vignetting
• ps: Plain version with shelf to depress the stop-down pin
• psv: Plain version with shelf and thin E/FE mount to minimize vignetting
• e: Embossed adapter body
• ev: Embossed with extra thin E/FE mount to minimize vignetting
• es: Embossed with shelf to depress the stop-down pin
• esv: Embossed with shelf and thin E/FE mount to minimize vignetting
• t: The text and E/FE alignment for 2nd-color filling adapter embossing
• sup: A simple printing support structure for the versions with a shelf

For example, for a plain M42 adapter with a shelf suitable for Mamiya Sekor SX lenses, print the ps or psv version and either enable support generation or include sup for support. A standard labeled M42 adapter would be a two-color print with e in black and t in a contrasting color (e.g., copper). Printed in standard PLA using a Bambu X1C with default settings, even the v versions seem plenty strong. The biggest issue is that dyes used in PLA often are transparent in NIR, so you'll need to check your PLA is truly opaque and paint it with something like Black 2.0 if it isn't.

Note that the E/FE mount here is designed to fit both the all-metal and plastic-insert (original NEX) versions of the E/FE body flanges. As a result, it may feel slightly loose on the older plastic-insert E mount bodies. If it is very loose, your mount's plastic part probably has been slightly deformed or even cracked by use of oversize adapters (most commercial adapters sold for NEX models and not A7RII, etc., were deliberately made with slightly too thick bayonet wings so they would feel tighter).