MOS Format Guide

Available Conversions

About MOS Format

MOS is the RAW image format used by Leaf digital backs, a line of medium format digital camera backs produced by Leaf (originally a division of Leaf Systems, later Creo, then acquired by Phase One). Leaf digital backs, including the Aptus, AFi, and Credo series, were designed to attach to medium format camera bodies from Hasselblad, Mamiya, and other manufacturers, providing high-resolution digital capture for professional photography. MOS files store unprocessed 16-bit sensor data from Leaf's CCD sensors, which ranged from 22 to 80 megapixels depending on the model. The format preserves the complete, linear sensor readout along with metadata about capture settings, ensuring maximum flexibility for post-processing and color correction in professional workflows.

History of MOS

Leaf's history in digital imaging dates back to the early 1990s when Leaf Systems (based in Westborough, Massachusetts) was among the first companies to produce digital camera backs for medium format photography. The company's early products, including the Leaf Digital Camera Back and the Leaf DCB, were pioneering devices that brought digital capture to the studio photography market. The MOS format evolved as Leaf's proprietary RAW standard for storing unprocessed sensor data from these digital backs. Throughout the late 1990s and 2000s, Leaf produced a succession of increasingly capable digital backs: the Leaf Valeo series, the Aptus series (Aptus 22, 54, 65, 75), and the AFi series, each using MOS as their native RAW output format. Leaf was acquired by Creo Products in 2003, which was itself acquired by Kodak's Graphic Communications Group in 2005. In 2009, Phase One completed the acquisition of Leaf's digital back business from Kodak, consolidating two of the three major medium format digital back manufacturers under one company. Under Phase One ownership, Leaf introduced the Credo series digital backs, which continued to use the MOS format. Eventually, Phase One unified their product lineup under the Phase One brand, and the Leaf brand was gradually phased out in favor of Phase One's own IIQ format. Despite the discontinuation of the Leaf brand, MOS files remain important for photographers who used Leaf systems, and support continues in major RAW processing software.

Key Features and Uses

MOS files store unprocessed, linear sensor data at 16-bit depth from Leaf's CCD sensors, which were known for their excellent color accuracy and tonal reproduction. The format captures the full dynamic range of Leaf's medium format sensors, which provided approximately 12-13 stops of dynamic range depending on the model. MOS files include comprehensive EXIF metadata covering all camera and digital back settings: aperture, shutter speed, ISO sensitivity, white balance, lens information, and more. The format stores the raw Bayer mosaic data from the sensor, allowing complete control over demosaicing, white balance, and color processing during post-processing. Leaf's CCD sensors were particularly valued for their color rendition and smooth tonal transitions, characteristics that are fully preserved in the MOS RAW data. File sizes range from approximately 45 MB for the 22-megapixel Aptus 22 to over 160 MB for the 80-megapixel Credo 80, reflecting the large sensor resolutions of medium format digital backs.

Common Applications

MOS files are primarily found in professional photography archives from studios and photographers who used Leaf digital backs during the 2000s and early 2010s. Commercial and advertising photographers used Leaf Aptus and AFi backs for product photography, catalog work, and advertising campaigns where the medium format sensor's resolution and color accuracy justified the investment. Fashion photographers used Leaf systems for editorial and beauty work, where the CCD sensors' smooth skin tone rendering was particularly valued. Studio portrait photographers appreciated Leaf backs for their excellent color science and tonal reproduction. Architectural photographers used Leaf digital backs on technical cameras for precise perspective control combined with high-resolution capture. Fine art reproduction and archival photography projects used Leaf systems to create high-fidelity digital copies of paintings, photographs, and documents. Converting MOS to widely supported formats like TIFF, JPG, or PNG is essential for sharing, web publishing, and long-term archival, as MOS is a specialized legacy format. Capture One (developed by Phase One, which acquired Leaf) provides the best processing support for MOS files, with Adobe Lightroom and other RAW processors also offering compatibility.

Advantages and Disadvantages