Dark field astrophotography

Darkfield is a photographic term that is required by the unique nature of CCDs (digital cameras). CCD can convert optical images into digital signals, but the problem is that CCD will output even when it is not exposed to any light. This output is called undercurrent. If you shoot in a bright environment (daytime), undercurrent can be ignored. But in night photography, especially in astronomical observations, undercurrents need to be removed for high accuracy. Therefore, when shooting, you need to use the same parameters as the official shooting, put the lens cap on and shoot again. This shooting is called dark field shooting.