REFERENCE : CHIEF RflY
Fig. 3.52. Spot-diagrams of a classical Bouwers-Cassegrain with weak achromatising lens (400 mm, f/3.0 - f/6.0), as shown in Fig. 3.50
Figure 3.53 shows the preferred variant in two versions, "long" and "short". The only difference is the position of the stop, the "long" version having the conventional stop position quasi-concentric to the meniscus, the "short" version the stop at the meniscus. Since the system is aplanatic it is uncritical for the monochromatic third order aberrations where the stop is placed; and, as we saw in Fig. 3.36, the residual transverse chromatic aberration (C2 in Eqs. (3.223)) is unaffected by the stop shift because C1 is corrected.
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