M100
Soon after Hubble first began sending images from space, scientists discovered that the telescope's primary mirror had a flaw called spherical aberration. This flaw caused some of the collected light from celestial objects to be scattered, resulting in fuzzy images. In 1994, NASA released these two images of M100 taken with Hubble before (left) and after (right) the spherical aberration problem was corrected.
For more information about Hubble’s observations of M100, see:
hubblesite.org/contents/news-releases/1994/news-1994-02.html
hubblesite.org/contents/news-releases/1994/news-1994-49.html
hubblesite.org/contents/news-releases/1994/news-1994-03.html
hubblesite.org/contents/news-releases/1994/news-1994-01.html
Credits: ESA/Hubble & NASA