Zernike focussing

Zernike focussing

Image moment A4 vs. focus position. Slope is constant


Focussing using simplified Zernike expansion

The focussing of both telescopes now uses a procedure described in PASP 118, 1165 (2006):

An extra- and an interafocal image of a star is taken, A4 is calculated and the optimal focus is read of the graph to the left.