Simmod M42 to EF CONVERSION MOUNT

M42 lenses were designed around a threaded interface.

This system converts that interface into a fixed EF mount.

The Simmod SimMount M42 to EF Conversion Mount is a precision-engineered solution that enables M42-threaded lenses to operate on Canon EF and EF-S mount camera systems, while maintaining proper mechanical alignment and focus accuracy.

A Controlled Conversion System

This system introduces a structured mounting solution to an inherently variable thread-based interface.

The conversion consists of two primary components:

• A brass EF mount

• An aluminum sub-mount

The sub-mount installs onto the lens and acts as the contact surface for the EF mount. The EF mount can then be rotated, aligned, and fixed in position before being secured. (simmod)

This allows the user to orient the lens correctly relative to the camera body.

Mounting Method

• The M42 lens threads into the sub-mount

• The EF mount is seated onto the sub-mount

• Three set screws secure the EF mount to the sub-mount

• External notches allow additional tightening and positioning control (simmod)

The set screws do not contact the original M42 threads.
All pressure is applied to the sub-mount to preserve the integrity of the lens mount. (simmod)

Mechanical Performance

• Maintains infinity focus

• Allows fine adjustment via included shims

• Provides a fixed EF interface once secured

• Designed to maintain coaxial alignment between lens and camera (simmod)

This ensures consistent optical performance across different lenses.

Construction

• EF mount: solid brass

• Sub-mount: billet aluminum

• Matte black finish to reduce reflections

The combination of materials provides durability while maintaining dimensional stability under use. 

Compatibility

• M42 screw-mount lenses

• Canon EF and EF-S camera bodies (B&H Photo Video)

No electronic communication is supported.
This is a fully mechanical system.

System Behavior

The SimMount converts a rotational thread-based mounting system into a fixed, indexed mount, allowing consistent lens orientation and repeatable mounting.

It does not alter the optical design of the lens.
All changes are mechanical and interface-based.

Included Components

• Aluminum sub-mount

• Brass EF mount

• Set screws

• Allen key 

A mechanical solution for converting M42-threaded lenses into a fixed EF mount interface while maintaining alignment and focus accuracy.