Lenses for video surveillance and image processing The performance of a video camera, especially the image quality, is highly dependent on the quality of the lens used.
The quality and processing of the lenses used in the lens provides a high quality component for surveillance cameras and cameras used in production and image processing. In other words, a very high quality camera can never take advantage of it if the lens used is inferior.
Features of a high-quality camera lens are IR correction, little edge distortion, high light intensity, no vignetting, hardly any aberration and solid processing.
Differences from fixed focal lengths to variable focal lengths
Until 15 years ago, the lens was selected according to the application: Here, the required viewing angle, which the surveillance camera has to cover, was determined on site and converted into the focal length after conversion. So a lens with a fixed focal length was used.
At an object distance of 30 meters and a horizontal viewing angle of 30 meters, a lens with 6.5mm focal length was used (1/2 "cameras).With the production of lenses with variable focal length tedious on-site visits and calculations, but at the expense of the lens quality accounted for.
With the increasing number of different camera designs, we dome versions and bullet versions, the end of the fixed focal length was sealed, as these cameras are always delivered with a lens, and there is no way to change the lens.Only box cameras and video cameras in the field of production monitoring still use the fixed focal lengths.
In terms of quality and luminous efficacy, the fixed focal length lenses are superior to those with variable focal length.
IR corrected lenses
Surveillance cameras usually work 24 hours a day. To see objects even in the dark, infrared or built-in infrared LED's are used. They emit light, which is above the visible light spectrum and above the color spectrum. The lens registers the change of the light spectrum with the shift of the focus point. If the object was still sharply displayed during the day, it appears blurred under infrared conditions. So-called IR corrected lenses compensate for this. So the focus remains the same during the day and at night. It should always be ensured that the lens IR is corrected.
Lenses for megapixel cameras
With the production of megapixel cameras around 2005, the lens manufacturers were forced to respond to this trend and produce lenses with higher optical resolution, with the video surveillance still has no end. Meanwhile, resolutions up to 30 megapixels (7K) are available. To show an image of a multi-pixel camera, it requires a lens, which can also resolve the number of pixels, that is, the line resolution of the lens is crucial. This is often stated in the data sheets of the manufacturers with line pairs per millimeter.In video surveillance, the majority of resolutions of 2MP and 5MP have been established, which is no longer a challenge for the lens manufacturers.
Focal length and angle of view
In order to find the right focal length for a desired horizontal viewing angle, there are numerous calculation tools on the Internet that show the correct focal length after entering the camera sensor size and the desired angle.As a rough guideline and independent of the sensor, one can say that a 90 ° viewing angle (often required for indoor surveillance) requires a focal length of less than 3mm.