Celestron C9 - Repairing a loose secondary mirror

Problem:
Even with some C9s (Celestron 9"), the screw mechanism on the secondary mirror becomes loose over time and with proper use. The glued foam rubber loses its tension and hardens with aging. This causes the secondary mirror's entire attachment to the Schmidt plate to rotate loosely, along with the retaining ring.
Since, unlike older models, the secondary mirrors are now symmetrically ground, the rotation of the secondary mirror no longer significantly affects the image.

However, with continued use, the mirror rotates further and further out and can tilt and eventually fall out of the Schmidt plate.

In this case, however, one of the two retaining rings holding the Schmidt plate in place was missing.
Furthermore, with this telescope, the Schmidt plate was also dirty.

Solution:
Sometimes you can solve the problem yourself by removing the retaining ring and then carefully removing the secondary mirror. You can then carefully grasp the inner ring and tighten the mount again by turning the outer attachment. This only works, of course, if the thin rubber bands are still elastic and completely present.

Caution: Do not touch or even touch the Schmidt plate. Gloves are invaluable here.

However, if the foam rubber band has already hardened too much, this will unfortunately no longer help, as too much pressure will be required to tighten it, if at all. And pressure must not be applied to the Schmidt plate under any circumstances.
During a thorough inspection of this telescope, which we perform as standard on all repair telescopes at the beginning, we found that a missing foam rubber band was the cause of the loosening, and the Schmidt plate was also not firmly seated in its four holding points.
Unfortunately, these rubber bands (although the material is not rubber in the true sense of the word) are not readily available for purchase.

We make do with handcrafting and thin "rubber" plates. The advantage: all sizes can be cut to size.
After removing the Schmidt plate, unscrew the secondary mirror from the plate (wear gloves). It's important to note the markings indicating how the Schmidt plate should be positioned and what is inside and what is outside!!!
Once removed, you can now loosen the secondary mirror holder with light pressure and use the inner metal holder as a cutting template:




With the new ring and a lot of patience, screw the secondary mirror back into the Schmidt plate and then return the markings on the secondary mirror and Schmidt plate to their original alignment.

Since, as mentioned, the Schmidt plate was very dirty, you could clean the plate before installing the plate and secondary mirror. Extreme caution is required here, and any pressure or excessive friction should be avoided. Remove dust and microparticles from the plate beforehand with a blower!

Tip:
The original settings are: secondary mirror notch = 3 o'clock; plate marking = 5 o'clock, or 6 o'clock on some models. The secondary mirror marking must be parallel to the Celestron retaining ring of the Schmidt plate when closed.
Also make sure that the four holding points hold the plate and that all four are in contact with the plate, just enough contact to hold the Schmidt plate but not put under pressure.

Check, adjust, and the C9 is like new again.

A word about cleaning Schmidt plates:

A Schmidt plate rarely needs cleaning. Dust particles or small streaks do not affect its appearance!
The glass surface of the plate is coated! This coating reacts sensitively to mechanical and chemical stress.
We only clean Schmidt plates in exceptional cases!
If you absolutely want to clean the plate, please observe the following points to avoid causing permanent damage:

Do not allow (skin) oils or acids to come into contact with the plate - wear gloves,

Human skin is a carrier of oils and acids!


The surface of the plate is coated with a coating. Never use household cleaning products - no glass cleaners, dish soap, or similar.
Use Optical Wonder and a lint-free microfiber cloth.
Do not apply pressure to the plate.
Never wipe away particles; always blow them away.
Do not blow with your mouth, only with a blower.
Pay attention to markings and retaining plates to ensure they are returned to their original position.

If this is too much work for you, please feel free to contact us for inspection or repair (for a small fee).