In most cases, industrial MV cameras use the C-mount connection for mounting the lenses. For very compact 'sugar cube' cameras, the CS mount is also used to provide a little more installation space for the camera electronics. The CS mount is the dominant standard for surveillance cameras. The exact flange focal length for C-mount is 17.526 mm.
The C-mount connection is an inch thread, known under the specification 1-32UN-2A. It has a 1 inch outer diameter, 32 TPI (threads per inch = 32 threads per inch, 0.784 mm per thread) and a 60° flank angle. It corresponds approximately to the metric thread M25.4 x 0.8 mm with 60°.
The connection standard is historically characterised by the beginnings of American film technology and has survived to this day in video technology and image processing. The C-mount thread was standardised by the Society of Motion Picture and Television Engineers (abbreviated: SMPTE) and the American National Standards Institute (abbreviated: ANSI).
The C-mount thread has a flange focal distance of 17.526 mm, whereas the CS-mount has only 12.5 mm. It has a shorter flange focal distance and therefore a shorter design. All other dimensions and diameters are the same as for the C-mount thread.
By using a C-CS mount adapter, any CS mount camera can use almost all C mount lenses (as long as they do not have a screw-in thread that is too long and can no longer be screwed completely into the 5mm ring). The use of CS-mount lenses on C-mount cameras is not possible. Due to their short flange focal distance, CS-mount lenses are ideal for constructing extremely wide-angle lenses at low cost. This is particularly important in surveillance technology.
Particularly compact and low-cost single-board camera modules use lenses with an S-mount connection. These are lenses with a thread diameter of M12 x 0.5 mm. They are also known as 'M12x0.5 lenses'. These miniature lenses are used in everything from webcams to OEM industrial board cameras. Despite their low price, their optical quality is not necessarily poor. Colour corrected 5 megapixel lenses are also available. S-mount lenses usually have no aperture, i.e. they are maximally open. S-mount lenses can be used with camera sensor sizes of 1/2', 1/3' or smaller. In addition to the lack of an aperture, these lenses do not usually have a focus ring: in many cases, S-mount lenses are focused by screwing the lens in and out of a threaded shaft. Compact screw mount lenses such as the S-mount are also available in other thread diameters such as M17, M14, M13, M9, M8, M7 etc.
The F-mount connection refers to Nikon's bayonet system developed in the late 1950s. The flange focal length is 46.5mm. The F-mount, like the M42 thread, is mainly used for high-tech cameras with particularly large sensors that offer particularly high resolution with large pixels. This applies to industrial area scan and line scan cameras. Depending on the manufacturer, M42 used to have different dimensions, e.g. 45.46 mm or 45.5 mm. For industrial cameras, however, this is not an issue, as the lenses available are adapted to the cameras with suitable tubes, which do not provide the required flange focal length anyway with their compact housings. Important to know: There are two different types of M42 mount. The T2 mount has a 42mm thread with a pitch of 0.75mm. This should not be confused with the T1 camera mount M42x1 mm. The threads are not compatible!
In terms of their dimensions, lenses rarely end at the contact surface of the camera, but rather dip into the camera body with the last lens group.
The focal length is the distance from the top of the last lens to the image sensor.
This is often the case with wide-angle lenses.
There are often problems with the back focal length when using CS-mount cameras with C-mount adapter + wide-angle C-mount lens. Some lenses touch the inner edge of the C-mount adapter in certain focusing positions.
3-chip cameras with a multi-part prism in front of the sensors, too, do not permit that the optics stick into the interior of the camera. Special three-board lenses typically provide a special colour correction and avoid this problem by means of a different lens design. Of course they can also be used as "normal optics" with low back focal length at any time.
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