New mirror locking device for the C14

 

Problema

The previous system installed on my C14 gave some good results. But the rigidity between the mirror plate and the rear cell of the OTA was not as good as expected due to the small diameter of the rod and its screweing on one point. Furthermore, the long rod outside the OTA makes the storage difficult with the system on. So I decided to build a new device more compact and rigid, specially designed to permanently remain in place.

The system

The constraint was to start again from the two existing holes. These ones taped at first to 1/4"-20tpi by Celestron were taped again to a metric M10 during the first run. So I would not either need to make a new machining or neeed to disassemble the OTA a second time. The device might need a little amount of adjustment depending on the optical combinations.

The sytem is composed of three part made of stainless steel :

The set-up is the following :

Firstly, the focus is approached with the original knob on the rear cell of the C14. The fine focus should be done later with the crayford focuser. Secondly, the M10 threaded rod is manually screwed up to the rear face of the mirror plate. Thirdly, the nut is firmly screwed for locking the rod in place. Finally, the thumbscrew is inserted into the rod and screwed into the tap of the rear plate. Its tightening completely locks the system.

The set-up in images (gif) :

The rod should be threaded along a 6 mm run. This latitude is needed to compensate the variations of the mirror position according to the backfocus of the focal reducers.

In use

This new locking device is really efficient. From now on, it is permanently mounted on my scope for a f/7 configuration. The focus is now only done with the crayford focuser. The collimation throughout the night should be greatly improved. But it is too soon to express a real opinion in view of the lack of clear nights since the installation ! To continue !