The mirror has to be carefully ground and polished (figured) to an extremely accurate shape, usually a paraboloid, although telescopes with high focal ratios may use spherical mirrors since the difference in the two shapes is insignificant at those ratios.
The mirror has to be carefully ground and polished (figured) to an extremely accurate shape a paraboloid, although telescopes with high focal ratios may use spherical mirrors since the difference in the two shapes is insignificant at those ratios. This is usually.