The focal length of a spherical mirror is R/2. The focus is not perfectly sharp, but gets sharper if the mirror shape approaches a parabola. Finally, for a symm

The focal length of a spherical mirror is R/2. The focus is not perfectly sharp, but gets sharper if the mirror shape approaches a parabola. Finally, for a symmetrical bowl, the effect is greatest at high noon, since off-axis rays are not focused to as intense a spot as rays parallel to the bowl axis.