C-mount
The C-mount consists of a one-inch diameter cylinder threaded to a pitch of 1/32-in, or 32 threads per inch. It was designed specifically for cine lenses used on 16mm cameras.
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| common 1950s amateur 16mm cine camera; lens turret with 3 viewfinder lenses and 3 C-mount taking lenses image by matias_e (Image rights) |
Some of the better quality cameras had a turret with a capacity for two or more lenses for making rapid changes in focal length. Though zoom lenses were available in the 1940's, they were very expensive and involved some optical compromises, so were not widely used until they had achieved better and more consistent quality at lower prices. After this was achieved, they eventually came to displace the turret in the 1960's, particularly in cameras for the amateur film maker.
The "C" designation derives from the evolution of the mount from its "A" and "B" predecessors. All shared the same thread and diameter, but had different mounting depths; the three are not interchangeable. A-mount and B-mount lenses were used primarily on early Filmo and Victor cameras. Thread depths varied from maker to maker, but the proper A-B-C distinction lies not in the total thread depth but in the distance from the flange seat of the lens barrel to the innermost thread. The C-mount eventually became the standard mount for higher-quality amateur 16mm cine cameras.
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| Schneider 1:1.5 25mm Xenon on Micro 4/3 adapter image by mr. Wood (Image rights) |
Cine cameras were often equipped with superb C-mount optics made by renowned lens makers like Taylor-Hobson, Dallmeyer, Meyer, Angénieux, Elgeet, Berthiot, and Schneider. Wollensak also made some fine cine lenses.
The C-mount was later used for video cameras, including those intended for surveillance. Some of these have a sensor area much smaller than the 16mm frame, and thus do not require such a large image circle from the lens.
In this century, people have begun to experiment with C-mount lenses on digital (still) cameras fitted with the Sony NEX, Nikon CX, Pentax Q or µ4/3 mounts (lens adaptors are widely available). They are likely to find the older uncoated lenses more satisfactory for bokeh experiments; and that such zoom lenses as were made in C-mount, like the Berthiot, are probably much too bulky and heavy to be attractive or even suitable. Meanwhile, the image circle of many of the newer lenses is unlikely to cover the entire area of the image sensor without serious vignetting.
