ddi in which the second term is the value for a classical Cassegrain. The increase in sensitivity due to the RC form is modest, 17.2% for the above values. The increase in (6S2)rc over (6S2)d is 13.8%. For large departures from the classical form, bs2 dominates over the fixed terms in (3.403) and the effect on the spherical aberration becomes more nearly proportional to bs2 — (bs2)c;.
For the Dall-Kirkham (DK) form, (bs2)^K = 0 and (3.403) reduces to d(Sj )2
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