Minimum illumination of black-and-white camera

The minimum illumination is also an important parameter to measure the quality of black-and-white cameras. Sometimes, the word "minimum" is omitted and referred to as "illuminance" for short. The minimum illumination is the scene brightness value when the brightness of the shooting scene is low enough to make the video signal level output by the camera low to a specified value. When measuring this parameter, the maximum relative aperture of the lens should also be specially indicated. For example, if F 1.2 lens is used, when the brightness value of the shooting scene is as low as 0.04LX, the amplitude of the video signal output by the camera is 50% of the maximum amplitude, that is, it reaches 350mV (the maximum amplitude of the standard video signal is 700 mV), then the minimum illumination of this camera is said to be 0.04LUX/F 1.2. If the brightness value of the shot scene is low, and the amplitude of the video signal output by the camera is less than 350 mV, it will be reflected on the monitor screen, and it is difficult to distinguish a layered and gloomy image.

Due to the non-uniform market specifications, the low illumination characteristics of some cameras with low illumination index may not be as good as those with slightly higher illumination index. The reason is that the criteria used to determine the low illumination index are different. Still taking the above example as an example, if the amplitude of the video signal output by the camera is reduced to 30% of the maximum amplitude (that is, 2 10 mV) as the measurement reference, the brightness value of the photographed object can be further reduced, for example, 0.03LX If the optical lens is further replaced with a lens of F 1.0, the brightness value of the photographed scene can be further reduced due to the increase of luminous flux.

It can be seen from the above analysis that, regardless of the measurement standard, it is impossible to accurately draw the conclusion that which camera has better low illumination characteristics only by comparing the nominal illumination value of a certain brand camera with that of another brand camera, because the relative aperture of the lens they use may be different from the specified value of the output video signal. Therefore, the minimum illumination index can only be used as a reference when designing and purchasing equipment.