Canon EF-M + M42 lens

COMPATIBLE MF MA TS

M42 lenses can be easily mounted on Canon EOS-M cameras.

Some simple calculations show that you'll need a 27.46mm adapter ring with an EF-M and M42 receptacle respectively.

One thing worth mentioning: some M42 lenses have a small lever which is responsible for operating the diaphragm. On the simpler, older M42 lenses the shutter will react according to the values set on the calibration dial only when this bit is pressed in. Not all adapter rings are fit for these, since there are two versions manufactured: one with aperture ring and one without it (this issue usally comes out with older Helios optics, the newer M42 lenses have an A-M switch, which allows using full manual mode, thus the aperture will be on the set value without having to use a separate bit).

The aperture ring can cause problems in one more case: if the lens has an aperture value feedback mechanic (a small sticking out red lever). This lever may touch the bezel and get the whole aperture control stuck. The SMC Takumar 1.4/50 is also has this feature, which means it needs an adapter without a bezel or you'd need to sand off a few milimeters from it. On the figure below you can see an adapter without a bezel, it's clearly visible why you'd have troubles with the other type.

As for the adapter ring brands, there is a huge assortment of them from noname ones to major manufacturers' solutions.

In most converters, the M42's threaded receptacle is a separate ring within the whole unit, which is fixed by three small bolts. After loosening the bolts, the thread can be turned within the converter, allowing to set the lens precisely, with the numbering on top.

Thanks to the difference in flange focal depth, tilt-shift adapters are also available on eBay:

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