Legault has a 20" scope he uses for his images. The camera at Kirtland AFB in New Mexico that took the black and white image of Columbia trailing plasma before it imploded on reentry was heralded as "amazing" yet they have a 32" scope that they use to track "space debris." The camera that took that photo was a tracking camera and they were testing a tracking mount at the time. There are always rumors floating around of images of the Tiangong good enough to see the docking mechanisms, which if my math is correct needs a 30" aperture at 300 miles away to get more than pixels. Adaptive optics may mean a smaller mirror is needed. If amateurs can see a spacewalking astronaut from the ground with off the shelf gear I can only imagine what we have pointed at this stuff and what it can make out. My stuff is not nearly this good, but I can dream. Googling "first image of the ISS from the ground" lead me to this page. I had to waste a bit of time there.