Check that the secondary mirror is in the center of the tube and thus in the center of the primary mirror.

Product Description
Check that the secondary mirror is in the center of the tube, and thus in the center of the primary mirror.

When adjusting, the secondary mirror must be exactly centered on the optical axis. Before collimating, use a ruler or similar device to measure the distance to the edge of the secondary mirror strut. The center point can generally be the center of the center screw or the edge of the secondary mirror mount.

The correct distance can then be adjusted using the side knurled screws.

Only then can the secondary and primary mirrors be adjusted with sufficient precision.

Provided the focuser is not tilted.

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