Repairing a ETX 125

[Chriske]

Busy repairing a 125mm Maksutov
It is one of the 'travel instruments' from our local observatory.
From what I've been told someone has dropped it on the ground...🙄...

First thing I've noticed was a major image tilt during focusing. I know this is common issue with these scope, even SC have a very small image tilt. But with this little scope it was severe. Stars moved more then halve the field of view during focusing. On top of it there was gigantic coma.
Work to be done.

This Mak ETX125 has no collimation bolts at the outside of the tube. So I completely took it  apart to see what had happened during it"s 'free-fall'.
First thing I've noticed that the primary mirror could be tilted in it's holder. With the aid of its central threaded ring I pushed it back toward it's holder.
After re-assembling there still was coma in the centre of the FOV. Took it apart again and bought a electronic collimator from OCAL.
Also printed a few rings to hold this ETX on a mount any mount. I had to go this way because there's no way to support the scope after removing the lower part of this ETX.
I also printed a eyepiece holder because the focuser also is part of that lower part.
This ETX (22 years) old is not designed for easy collimation if something happens...😡
If I'm not mistaken the latest ETX version do have easy access collimation bolts at the back of the scopes.

Waiting for clear skies to do final collimation....

[Chriske]

I hope this topic will help others repairing or collimate their Mak if needed.

 

 

 

 

 

 

 

[Chriske]

Only now I see that someone has already tuned this scope in the past.
The (red)seals of two collimation bolts are broken. The one on the upper left is intact the other two bolts have been rotated.
Normal factory procedure is that seals are applied after collimation is completely done.

[Chriske]

This OCAL tool can  not be used on stars as I thought it would.
Initial collimation is done by pointing the scope at the sky during daytime. So I did.
Later on, during night, I found out that collimation was not perfect at all, although OCAL told me it was.
Some more collimation needs to be done.

I also found out I put to much tension on the mirror. Remember I needed to fasten  the mirror in it's holder, but doing so I pushed(screwed) to hard resulting in slight astigmatism.

Later on today I will perform final collimation not using this OCAL tool...🙄