Aberration Caused by the Errors of Alignment and Adjustment in Reflecting Telescope

The 2-mirror Cassegrain geometry has firmly become a standard tool for modern astronomical research. The alignment and adjustment of aplanatic (RC) Cassegrain telescope is therefore by far the most important aspect. The errors that arise in telescope through maladjustment are discussed and the aberrations are calculated for the 2.4m telescope which will be mounted at Gaomeigu. The tangential coma resulting from a lateral decenter δ(mm) is 1.123δ(mm) and the astigmatism is-0.00245δ(mm). While the coma from a rotation of the secondary about its pole is-0.00856 u"_pr2 where the u"_pr2 is the rotation angle in arcsec. The lateral decenter of the secondary also produces a lateral shift of the image as 25.067δ(mm). The rotation of the secondary through the angle u"_pr2 produces the image shift as 0.578 u"_pr2. The despace, change of the separat ion between the two mirrors, effects on the other parameters. The despace causes the aberration also. The spherical aberration in arcsec due to the differential△d₁ is given as 0.0924△d₁. The change in tangential field coma in arcsec due to △d₁ is given as 7.8586W △d₁. With the maximum semifield angle the view angle Wis 20', the largest tangential field coma shoule be 0.0457 △d₁.