I have been working in the observatory as time allows restoring a friends "Richard Woodard" 12" Meade optical tube assembly "OTA". Disassembly of the OTA was performed down to ever last bolt. Putting the OTA on a diet by removing past balance bars and accessories was performed to get the weight reduced. Cleaning and painting the tube was performed with a flat black interior applied to help with reflections. There was some chipping damage of the corrector plate around the cork pads used to retain the lens. So, allot of glass flakes had to be removed from the tube and mirror. New adjustment screws were installed in the cell that holds the corrector lens which will now allow adjustment of the corrector for centering and better retention of the lens. This required drilling and tapping new locations for the adjustment screws in the ring.
In the OTA base four holes were drilled in the casting to allow for cooling fans. Studs were installed to allow removal and maintenance of the fans without disassembly of the OTA. The cooling fans were installed to withdraw air from the OTA to cool the mirror to ambient temperature and also disrupt the boundary layer of warm air that forms on the main mirror when observing. Filtered vents were installed in the OTA under the main dovetail plate with the theory to help keep moisture and light out. The fans can be regulated at three speeds to aid control of the airflow and are operated remotely.
The mirror support was cleaned and a thin layer of high vacuum grease applied. The mirror was cleaned and reinstalled into the tube. The stock focuser was cleaned and reinstalled with plans to upgrade that in the future for an EAF focuser system. The corrector lens was cleaned and reinstalled into the new adjustable pads with a cleaned secondary mirror as well. "Bob's Knobs" were installed in the secondary mirror assembly to help with the ease of collimation. Although a little harder to make very fine adjustments the of easy of access and adjustment using Bob's Knobs is a good trade off especially when working alone.
The mounting dovetail bar was drilled and tapped to allow installation of set screws for adjustment of the OTA in a dual scope configuration and also "Cone Error Correction".
A Tri-Bahtinov mask was purchased to aid in collimation using a star. This proved to work very well with a one person collimation. Using a cell phone I use Teamviewer to see the camera view of the PC running the camera and viewed the diffraction spikes while standing on a ladder in a position to make adjustments to the secondary mirror. This was tedious but working very well.
Continued adjustments and collimation will take place after the final focal reducer & camera is chosen and the correct back focus is achieved. Trials are ongoing at the native F10 focal length and additionally with a hard to find Meade F3.3 focal reducer that I purchased years ago.
Experiments with the cooling fan system and internal tube currents are moving along and I have observed a remarkable improvement in scintillation when using the tube fans at a low speed. Not long after shutting the system off the scintillation increases markedly. No vibration effects have been noticed when the fans are on. Additionally cooling of the optics with the fans after rollout of the scope trolley has been great noted by the ability to perform an auto focus quickly after rollout with no noticeable change in focus for a good period of time before requiring another focus run. Mirror shift has been minimized as much as possible with the high vacuum grease application and setting the mirror with the OTA spring and the lock spring set to help hold the mirror as much as possible. Much less shift has been noted after long slews. The addition of a Crayford focuser will also help this problem allowing repeatable focus without moving the mirror.
