Other Optical Combinations

Abstract

In this section we show that it is possible to realize an aplanatic Schmidt–Cassegrain telescope using only spherical mirrors. First, we suppose that all of the parameters for the Cassegrain combination are derived as shown in Chapter 4. That is, starting from the absolute value of the focal length f ₁ of the primary mirror S ₁, the required total focal length f _t of the whole combination, and the fixed distance em between S ₁ and the focal plane (see Figure 8.1), we determine the focal length f ₂ = γf ₁ of S ₂ as well as the distance −βf ₁ between the two mirrors using the relations