Apochromatic Telescopes are a type of refracting telescope that have a better correction of chromatic and spherical aberration than the more common achromat lens. The lenses in an apochromatic telescope will bring light of three different frequencies to a common focus. This should get you a much cleaner view of anything you're looking at in the night sky. If you plan to image with this type of telescope, you will need a field flattener or reducer-flattener. Doing so can get you incredibly crisp images.