MOS

MOS traces back to Leaf, a Massachusetts-based company that shipped one of the earliest medium-format digital camera backs, the Leaf DCB1, in 1991. The MOS extension itself became associated with Leaf’s raw output through the Valeo family of portable digital backs launched from 2002 onward, and continued through later Leaf lines including Cantare, Volare, and Aptus. Leaf built its business specifically around high-resolution backs for Hasselblad, Mamiya, and Contax medium-format camera bodies.

Structurally, MOS uses a TIFF/EXIF base but does not fully comply with the TIFF standard, and it stores raw data as a single grayscale sensor plane — uncompressed or with JPEG lossless compression — reflecting the pre-demosaic Bayer data straight off the back’s CCD sensor. Phase One acquired Leaf from Kodak in 2009, and the Leaf and Mamiya brands were later consolidated under Phase One, with subsequent Leaf-branded backs eventually adopting Phase One’s own IIQ format instead of MOS.

That corporate history matters directly for archival planning: MOS is now a format tied to hardware nobody manufactures anymore, from a brand absorbed into a larger company years ago. Leaf’s own raw converter software is effectively frozen in time, and while Capture One and Adobe Camera Raw still handle most MOS files, compressed variants from certain Leaf backs are already outside Camera Raw’s support. A DAM holding legacy medium-format archives with MOS files should treat DNG conversion as a near-term priority rather than an eventual nice-to-have.