Four Thirds Lens Adapters: Pentax M42 Lenses
The four thirds lens adapter for Pentax M42 lenses lets you attach this lens on camera bodies which have a different mount, and a depth of flange which is either equal to the M42 or lesser. The adapter will work with almost all M42 lenses, except those lenses which require a lock up for the mirror.
The Role of the Pentax M42 Lens
The Pentax M42 lens four third adapter has a screw thread diameter of 42 mm and a thread pitch of 1 mm. This type of mount was first used for a particular type of Zeiss lens, and then it became a standard mount for Pentacon cameras. Many other manufacturers later also started using this mount standard, as there was no proprietary attached to it. In the United States, the M42 mount was extensively used by Pentax and hence it got its name. It is also known as the "Universal thread mount."
Due to the popularity of a wide range of Pentax M42 lenses, its four thirds adapter has proven to be quite useful, as you can attach the lenses to a camera having a different mount. The aperture of the lens can be manually controlled by rotating the lens aperture ring.