The telescope also had a chromatic aberration. Different colors of light focus at different points when they pass through a glass lens. This causes a fringe of color to appear around bright objects.
Though many duplicated Galileo’s design, not everyone was as skilled as he was at making telescopes. Bad craftsmanship often caused confusion as people looked through telescopes and saw blurry images or objects that weren’t really there. Plus, glassmaking techniques at the time were much cruder than they are today, and the even the best lenses were far from perfect.
Galileo also commanded such respect that many people simply decided that he’d seen all there was to see in the heavens, discouraging further exploration. They didn’t realize that Galileo had barely skimmed the surface of the wonders waiting to be discovered.