dd1 /i rad
where N is the f/no of the primary of focal length /'. At the best focus (BF), the disk of least confusion is one quarter of d(5u'p)GF,Si at the Gaussian focus. A classical telescope with N = 10, m2 = ±4 and ddi//' = 10-3 or ddi//i = 4 ■ 10-3 gives from (3.409) with the second term of the square bracket zero and d(5u'v)GF = -6.188 arcsec
These values correspond to a despace of 10 mm in a 1 m telescope with f = 10 m, the corresponding image shift being 170 mm according to (3.398).
If Eq. (3.406) is expressed in terms of the fixed parameter / while f varies with m2, then d(S7 )2
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