George Abell was an inspirational scientist. For his PHD thesis in the 1950s he reviewed photographic plates taken by the National Geographic's Palomar Sky survey, at the Palomar Observatory in Southern California. He had noticed that galaxies tended to form clusters, and it was this rich distribution across the sky that he wanted to catalogue. The criteria that he used was at least 50 galaxies clustered together within a specific magnitude range and distance. Ultimately he not only spotted a huge number of galaxy clusters, but he also observed a second order of clusters, i.e. that the clusters themselves clustered, and were separated by something (dark matter). This observation influenced cosmology and our future understanding of the universe.

So, back to this image: taken over 4 whole clear nights (but with the last night discarded due to turbulence) this is a stack of 333 x 3 minute subs. It isn't as good as the Hubble image (https://science.nasa.gov/asset/hubble/coma-cluster-full-mosaic) but it does include over 100 galaxies. According to the "Seti Astro Suite" software, the furthest galaxy in this image, toward the centre, is "[ANM98] +1.08-0.22", which is 7.3 billion light years away.