Canon EF vs. M42 Screw Mount
Comparing 2 standards across 12 specifications. 12 key differences identified.
The Canon EF Mount (introduced in 1987 for the EOS autofocus SLR system) revolutionized photographic camera design as the first 100% all-electronic lens mount, eliminating all mechanical aperture linkages and autofocus drive shafts. Featuring a 44.0 mm Flange Focal Distance and a large 54.0 mm throat diameter, over 150 million EF lenses were manufactured over 33 years.
The M42 Screw Mount (also known as the Universal Screw Mount or Praktica/Pentax Thread, standardized under DIN 4503) is a standardized metric threaded lens interface featuring an M42 × 1.0 mm thread pitch and a 45.5 mm Flange Focal Distance. Popularized by Asahi Pentax Spotmatic and Soviet Helios-44 lenses, it is the most adapted vintage manual lens standard in mirrorless photography.
Specification Comparison Table
12 Parameters| Parameter / Spec | ||
|---|---|---|
|
Flange Focal Distance (FFD)
|
44.00 mm (1.732 in) | 45.50 mm (1.791 in) |
|
Inner Throat Diameter
|
54.00 mm (2.126 in) | — |
|
Bayonet Tabs
|
3 locking tabs with clockwise twist | — |
|
Electronic Interface
|
8 gold-plated electronic contacts (expanded to 11 pins on EF super-telephoto lenses for teleconverters) | — |
|
Internal Actuators
|
Internal USM (Ultrasonic Motor) in lens body + internal electromagnetic aperture diaphragm (EMD) | — |
|
Variants
|
EF (Full Frame), EF-S (APS-C with rubber bumper back-focus extension), EF-M (discontinued APS-C mirrorless) | — |
|
Camera Systems
|
Canon EOS-1D X Mark III, EOS 5D Mark IV, EOS 6D II, EOS Rebel series, Cinema EOS C300/C500 | — |
|
Thread Dimensions
|
— | M42 × 1.0 mm metric thread (42.0 mm diameter with 1.0 mm thread pitch) |
|
Mounting Style
|
— | Direct screw-in thread (approx. 2 to 3 full revolutions to seat against flange) |
|
Aperture Pin Mechanism
|
— | Center spring-loaded pin pressed by camera stop-down lever to close iris during exposure |
|
Benchmark Cameras & Lenses
|
— | Pentax Spotmatic (Super-Takumar / SMC Takumar), Praktica L-series, Zenit-E (Helios-44-2 58mm f/2), Carl Zeiss Jena |
|
Mirrorless Adaptability
|
— | Adapted seamlessly to Sony E, Canon RF, Nikon Z, L-mount, Fuji X, and MFT via inexpensive passive aluminum rings |