The CS mount has a smaller back focal distance than the C mount, allowing for more space between the lens and the image sensor. This extra space is necessary to accommodate the smaller image sensors used in surveillance cameras. By moving the lens further away from the sensor, CS mount lenses are optimized for these smaller sensors and provide the appropriate focal length and coverage.

The CS mount uses a threaded connection, similar to the C mount, to attach the lens to the camera body. However, the thread diameter of the CS mount is smaller than that of the C mount, measuring 1/2 inch (12.5mm). This smaller size is another characteristic that distinguishes the CS mount from the C mount.

Another thing is that the checkerboard should be asymmetric. Ideally, you want to have an even number of squares along one side, and an odd number of squares along the other. This way the board's in-plane orientation is unambiguous.

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What is the optimal number of snap shots of different checkerboard position/orientation? Zhang uses 5 images only. I saw people suggesting 20~30 images with checkerboards at various angles, fills the entire field of view, tilted to the left, right, top and bottom, and suggested there should be no checkerboard placed at similar position/orientation otherwise the result will be biased towards that position/orientation. Is this correct?

Ideally you want to place your checkerboard at roughly the same distance from the the camera, as the distance at which you want to do your measurements. So your checkerboard squares must be large enough to be resolvable from that distance. You also do want to cover the entire field of view with points, especially close to the edges and corners of the frame. Also, the smaller the board is, the more images you should take to cover the entire field of view. So 20-30 images is usually a good rule of thumb.

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The C mount uses a threaded connection to attach the lens to the camera body. The lens is screwed onto the camera, and the threads ensure a secure and stable attachment. The mount has a 1-inch diameter (25.4mm), which makes it relatively small compared to other lens mounts used in larger camera systems.

Also, I would suggest that you try the Camera Calibrator app in MATLAB. At the very least, look at the documentation, which has a lot of useful suggestions for calibrating cameras.

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One advantage of the M12 mount is its wide compatibility with various lens types. Many lens manufacturers produce M12 lenses, offering a range of focal lengths and aperture options to suit different imaging needs. These lenses are typically designed for use with small image sensors found in compact cameras, surveillance systems, and other devices.

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The M12 mount typically uses a threaded connection to secure the lens to the camera body. The lens is screwed onto the camera, and the threads ensure a secure and stable attachment. This type of mount is known for its simplicity and ease of use.

The C mount is a standardized lens mount used in the field of professional video and cinema cameras. It was initially developed by Bell & Howell in the 1930s for 16mm film cameras and later adopted by other manufacturers.

The CS mount has the same flange focal distance as the C mount, which is 17.526mm. This means that CS mount lenses can be used on C mount cameras by utilizing a C-CS mount adapter, but C mount lenses cannot be directly mounted on CS mount cameras without an adapter due to the shorter flange focal distance of the CS mount.

The M12 mount has a flange focal distance of 12mm, which is the distance between the mounting flange (the metal ring that attaches the lens to the camera) and the image sensor. This short distance allows for the use of small and lightweight lenses, making it suitable for compact and portable camera systems.

If the accuracy you get is "pretty random" then you are likely not doing it right: with stable optics and a well conducted procedure you should consistently be getting RMS projection errors within a few tenths of a pixel. Whether this corresponds to variances of millimeters or meters in 3D space depends, of course, on your optics and sensor resolution (calibration is not a way around physics).

The M12 mount refers to a standardized lens mount commonly used in the field of digital imaging. It is a small form factor mount primarily used in compact cameras, webcams, and other small electronic devices that require interchangeable lenses.

It’s important to note that CS mount lenses are not directly compatible with C mount cameras without an adapter. However, the reverse is possible, where C mount lenses can be used on CS mount cameras with the appropriate adapter.

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I am trying to calibrate a camera using a checkerboard by the well known Zhang's method followed by bundle adjustment, which is available in both Matlab and OpenCV. There are a lot of empirical guidelines but from my personal experience the accuracy is pretty random. It could sometimes be really good but also sometimes really bad. The result actually can vary quite a bit just by simply placing the checkerboard at different locations. Suppose the target camera is rectilinear with 110 degree horizontal FOV.

I wrote time ago a few suggestions in this answer, and I recommend you follow them. In particular, pay attention to locking the focus distance (I have seen & heard countless people trying to calibrate a camera on autofocus, and be sorely disappointed). As for the size of the target, again it depends on your optics and camera resolution, but generally speaking the goals are (1) to fill with measurements both the field of view and the volume of space you'll be working with, and (2) to observe significant perspective foreshortening, because that is what constrains the solution for the FOV. Good luck!

One of the key advantages of the C mount is its versatility. It can accommodate various lens types, including 16mm film lenses, 1-inch format lenses, and smaller lenses designed for compact cameras. Additionally, with the use of adapters, it is possible to mount C mount lenses on other camera systems, expanding the range of available lenses.

Does the number of squares in the checkerboard affect the accuracy? Zhang uses 8x8 in his original paper without really explaining why.

The CS mount is a standardized lens mount commonly used in the field of surveillance and security cameras. It is an extension of the C mount and is designed specifically for cameras with smaller image sensors.

The C mount has been widely used in the past for film cameras and is still utilized in modern digital cameras, particularly in the industrial and scientific imaging fields. However, in recent years, other lens mounts like the PL mount and EF mount have become more prevalent in professional cinema cameras due to their ability to handle larger sensors and heavier lenses.

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Concerning variations on the parameter values across successive calibrations, the first thing I'd do is calculate the cross RMS errors, i.e. the RMS error on dataset 1 with the camera calibrated on dataset 2, and vice versa. If either is significantly higher than the calibration errors, it's an indication that the camera has changed between the two calibrations and so all odds are off. Do you have auto-{focus,iris,zoom,stabilization} on? Turn them all off: auto-anything is the bane of calibration, with the only exception of exposure time. Otherwise, you need to see if the variations you observe on the parameters are actually meaningful (hint, they often are not). A variation of the focal length in pixels of several parts per thousand is probably irrelevant with today's sensor resolutions - you can verify that by expressing it in mm, and comparing it to the dot pitch of the sensor. Also, variations of the position of the principal point in the order of tens of pixels are common, since it is poorly observed unless your calibration procedure is very carefully designed to estimate it.

CS mount lenses are widely available and specifically designed for surveillance and security applications. They offer a variety of focal lengths and lens options to meet different surveillance needs, including wide-angle lenses, telephoto lenses, and varifocal lenses. These lenses are typically used in closed-circuit television (CCTV) systems, video surveillance cameras, and other security applications.

Overall, the C mount remains an important and versatile lens mount, particularly in applications where compactness and flexibility are desired.

The C mount has a flange focal distance of 17.526mm, which is the distance between the mounting flange and the image sensor or film plane. This short distance allows for flexibility in lens design and makes it compatible with a wide range of lenses, including both prime lenses and zoom lenses.