Important for a precise adjustment of Newton is the exact position of the secondary mirror in the geometric center to the tube and primary mirror.

For precise Newtonian alignment, the precise position of the secondary mirror at the geometric center of the tube and primary mirror is important.

A ruler is sufficient for this, allowing you to measure the respective distance from the edge of the tube to the center of the secondary mirror (here, the center of the mounting screw). If this is not correct, the distance can usually be adjusted using nuts on the ends of the secondary mirror spider. To do this, loosen one screw at the opposite end and tighten the other.

The secondary mirror can also be removed, and there is a hole in the center of the secondary mirror mount that can be used for measuring.

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