How to take pictures of constellations dozens of light-years away from the earth?

First of all, correct the saying that no constellation is dozens of light years. Constellation is composed of the projection of stars on the celestial sphere, and there is no distance. The stars that make up the same constellation may be far apart, so a single star has a distance, and the constellation has no concept of distance.

A camera relies on a lens (or telescope) to receive light, and then focuses it on a photosensitive chip for imaging. No matter how far away, as long as the light can reach the camera, you can take pictures. Stars dozens of light-years away photograph the light emitted by stars decades ago. If this star explodes tomorrow, in our eyes, it will still exist for decades, and we won't know until the light generated by the explosion reaches the earth.