Why we check and adjust telescopes before shipping or release

We check and adjust every telescope before selling it so the new owner can get started right away.

Why do we do this?

Here's an example that occurs frequently:

With Newtonians, the fan mirror retaining screw may be bent at the factory. In this case, the telescope may have been adjusted at the manufacturer's facility, but it's not optimal.

The image shows how the secondary mirror support block (FSHB) deviates to the right relative to the secondary mirror holder mount (FSHA).

If we find such a telescope during inspection, the optimization process begins.

First, the secondary mirror is removed and a laser check is performed to determine whether the secondary mirror holder mount is orthogonal to the optical axis.

The laser beam should at least roughly fall on the center mark of the primary mirror.

Now, check the secondary mirror retaining screw (a tension screw).
 

It's clearly visible that the screw is bent.

If such a telescope hasn't been checked, the new owner will wonder why they can't adjust the Newtonian correctly. The secondary mirror tends to twist whenever one of the three adjustment screws (2.0 mm Allen key) is tightened.

The secondary mirror is reinstalled, and a sheet of paper is clamped between the secondary mirror and the primary mirror in the tube. This paper is intended to reduce irritating reflections and simplify the next steps.

The secondary mirror is aligned using a Cheshire eyepiece: First, the secondary mirror is rotated around the optical longitudinal axis until it appears as circular as possible in the Cheshire.


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Fig. Cheshire eyepiece

 

The secondary mirror is not aligned correctly.

The secondary mirror is now correctly rotated and adjusted.

The paper is then removed and the center mark is centered using the secondary mirror adjustment screws. During this process, check regularly to ensure the secondary mirror is still correctly positioned.

The primary mirror's center mark, unfortunately blurred (the bright mud patch in the center of the circles), was aligned to the center of the Cheshire rings.

The primary mirror is then aligned using a laser.

Now the telescope is finished and ready for use.