SIGMA PL to L-Mount Converter MC-31


SIGMA’s  PL to L-Mount Converter MC-31 begins shipping on February 27, 2020, retailing for $679 USD from authorized SIGMA dealers.

Quick review: The L-Mount Alliance consists of SIGMA, Panasonic and Leica. The L-Mount has a 20mm FFD and 51.6 mm ID. Full-Frame L-Mount cameras include Leica SL, Panasonic S1, S1R, S1H and SIGMA fp.

(By the way, by way of comparison, the Sony E-mount has an 18mm FFD and 46.1 mm ID.)


The MC-31 has an aluminum-alloy body with a strong brass mount and locking ring. The markings on the upper part of the converter use the same luminous paint as used on SIGMA cine lenses, making them easier to read in the dark.

If you’re using the MC-31 on the SIGMA fp camera (shown below), an additional screw thread ensures an even more secure connection between the adapter and the camera.

The reason is that the L-Mount is not a breech lock like the PL mount, and this extra screw keeps the adapter tight and secure from twisting even after long-term use.


The MC-31 has shims to adjust Flange Focal Depth on both the front and on the back side of the adapter. You can shim on the L-mount side (camera side) with the included shim kit, or on the PL side (lens side) of the adapter using standard ARRI ALEXA PL mount shims. This is unique for any mount adapter as far as I know, and it’s a really good idea.

Tripod and Lens Support

A removable support bracket with 1/4-20 threads lets you attach the MC-31 to a tripod, handgrip, camera cage or .

PL Lock

Most PL mount breech locks have a stopper pin to prevent overtightening. But sometimes the PL tabs of a lens can be too thin and the lens wobbles because you can’t tighten the mount past the stopper pin. The MC-31 has an adjustment to release the stopper pin so can tighten the breech lock further. Of course, be careful you don’t tighten to the point of not being able to loosen it again.

Directors Finder

MC-31 is the essential link to use PL lenses on the SIGMA fp: an awesomely mini camera for  stills, 4K 12-bit video, and directors finder.


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