Ask the photographer to answer! ! D90+ Sigma 10-20 Shoot the starry sky F4.5 ISO 1600 for 30s. Look carefully at the dots with red, blue and green colors on them and find out why! !

Three-color spots are just a little long exposure time.

Personal suggestion: the aperture should be smaller, about ISO400, exposure time 10 second, download 20 continuous shooting, and synthesize this software. It's as simple as that. Just a few buttons.

Some additional suggestions.

If you like to shoot the night sky, you'd better buy a regular 100 cable release.

Noise reduction must be turned off.

If there is still a lot of noise in 5 seconds, you should cover the lens, take 10 "dark pictures" in a completely dark place (such as under the bed), and load them into that software, which can help you reduce the noise.