Interfaces and Flange Focal Distance of Industrial Lenses
There are many different types of interfaces between industrial lenses and industrial cameras, commonly used interfaces for industrial cameras include C-mount, CS-mount, F-mount, V-mount, M42 mount, M58 mount, etc. The different interface types have no direct relation to the performance and quality of industrial lenses; they only differ in interface method. Adapters can generally be found to connect between various commonly used interfaces.
For example, most of our company's telecentric lenses and non-telecentric lenses use the C-mount interface, which is the most common international standard interface for industrial cameras. The C-mount is a 1-inch-32UN imperial thread connection, with a flange focal distance of 17.5mm. Our company's TTL39.2 series telecentric lenses use the F-mount and M58 mount, which are compatible with most large-format cameras.
Introduction to Flange Focal Distance
In an optical system, the distance from the vertex of the last optical lens surface to the image plane is called the flange focal distance, also known as the back focal distance. For different optical systems, their flange focal distances are different. Therefore, when installing lenses, the relative position of the lens to the camera needs to be adjusted to ensure that the distance from the sensor to the last vertex of the lens is in accordance with the flange focal distance requirement, thereby placing the image sensor on the lens's image plane.
Some industrial camera interfaces have fixed flange focal distances, such as the C-mount and F-mount. Here, we'll take the C-mount as an example to discuss the matching of lens and camera flange focal distance.
The flange focal distance of a C-mount camera is 17.526mm. When it is used with a C-mount lens, since the C-mount lens's flange focal distance design is also 17.526mm, the light rays can converge precisely at the chip position, resulting in clear imaging.
If the lens remains unchanged and the camera chip moves forward, to ensure that the light rays still converge on the chip to obtain clear images, we need to add a spacer between the lens and the camera to ensure that the light rays converge at the chip position.
If the lens remains unchanged and the chip moves backward, i.e., the camera's flange focal distance is greater than 17.526mm, at this time, the lens forms an image in front of the chip. If we want the light to focus on the chip to obtain a clear image, we can only continue to screw the lens into the camera. However, it is evident that this is almost impractical. Therefore, when the lens's flange focal distance is less than the camera's flange focal distance, a clear image cannot be obtained.
In mechanical manufacturing, due to the existence of tolerances, each lens cannot perfectly achieve the designed back focal distance, resulting in deviation in lens imaging, especially working distance. This is an unavoidable factor. To minimize this error, Opto Vision equips lenses with spacers to adjust the back focal distance to the optimal imaging position.
Based on the above theory, we can also adjust the working distance of telecentric lenses within a certain range by increasing or decreasing spacers. This adjustment has almost zero impact on the performance and magnification of the lens, which is also a characteristic of telecentric lenses. Regular non-telecentric lenses cannot achieve this effect.
For example, in Opto Vision's telecentric lens TTL11.5-25-50C, if you need a slightly larger or smaller than 50mm working distance, you can appropriately adjust the spacer to fine-tune the flange focal distance to achieve the required working distance while meeting your performance requirements.
FALenses Technology specializes in providing machine vision core hardware. You can go to the official website of FALenses Technology at https://www.falenses.com/ for more information.