Chromatic aberration does not occur in a mirror because chromatic aberration is caused by the different colors of a light being bent different amounts. Mirrors do not care about the different colors as they only relfect the light instead of refracting it.

The most chromatic aberration would occur with a single-lens refractor. However, today most telescopes employ at least two lenses, called achromats. These still incur significant chromatic aberration if the telescope has a short focal length to aperture ratio, called focal ratio. An easy way to determine if the telescope will have significant chromatic aberration is to divide the focal ratio of the telescope by the diameter of the lens in inches. A value of 5 or higher indicates minimal chromatic aberration; 3 to 5 is moderate aberration, and 3 and under is significant chromatic aberration. However, chromatic aberration is generally only obvious on bright stars or planets.

Chromatic aberration does not occur in a mirror because chromatic aberration is caused by the different colors of a light being bent different amounts. Mirrors do not care about the different colors as they only relfect the light instead of refracting it.

prime focus reflector

Newton realized that mirrors do not cause chromatic aberrations, and built a telescope using them.