[Kalkwasser]

In one of my practise questions I am asked to show the centre of curvature of the secondary lens. I took this means the radius that will sit behind the convex mirror however I am confused in that aren't the reflectors designed to be parabolic to prevent spherical aberration? Or is this only relevant for the primary reflector?

Many thanks in advance for your replies

[Stonebridge]

(Original post by Kalkwasser)
In one of my practise questions I am asked to show the centre of curvature of the secondary lens. I took this means the radius that will sit behind the convex mirror however I am confused in that aren't the reflectors designed to be parabolic to prevent spherical aberration? Or is this only relevant for the primary reflector?

Many thanks in advance for your replies

Some designs of Cassegrain have a spherical secondary mirror.
In fact there are various combinations of mirror types possible.
A quick look at Wiki will confirm this.
http://en.wikipedia.org/wiki/Cassegrain_reflector