These two examples will suffice to introduce the reader to possibilities for
practical four-mirror telescopes with spherical primaries. Wilson (1966) discusses
other four-mirror configurations; the interested reader should consult his text for
specifics.
6.5.b. PUPIL ALIGNMENT
In Section 6.3 we discussed the consequences of a misaligned secondary
mirror in a two-mirror telescope and showed that an error in its position (tilt,
decenter, and/or despace) introduced aberrations. In this section we consider the
consequences of a misaligned pupil and show that aberrations are again the result.
In the case of a four-mirro ...
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