From the Manufacturer
The Fotodiox M42-MFT Lens adapter allows you to place your favorite M42 Lens on your Micro Four Thirds (MFT) camera body. This adapter gives you the ability to use your irreplaceable prime lens and saves you the cost of purchasing new lenses. The adapters are precision made to insure the perfect fit. The lens will fit physically, but the automatic diaphragm, auto-focusing, and other functions will not operate correctly while using this adapter. In this case, -Inch stop-down mode-Inch will need to be used when metering, since the lens does not have the ability to have its aperture controlled by the camera body. You can shoot in manual or aperture priority mode. Infinity focusing is guaranteed.
If you have a SLR or DSLR camera and other maker/mount lenses, the Fotodiox Mount Adapters allow you to use your lenses on the film/digital camera body. Sharing lenses has some distinct advantages. Certain prime lens just can't be replaced, and you save cost of purchase lenses. Fotodiox offers a range of adapter from large format to smaller format digital adapters. Adapting larger format lens, i.e., large format - medium format, medium format - 35mm, excellent edge-to-edge sharpness; and the smaller 24x36 mm image field helps minimize the effects of lens distortion and aberration.