Restoration of 15” Reflector
Primary Mirror
Before the Primary mirror could be removed the scope was propped on a specially made truss to support the weight of the unbalanced tube. In the event, the mirror and weights that had to be removed represented quite a load and could possibly have caused damage to the drives had this precaution not been taken. This job was one of the “daytime” activities - good light was required to see all the fixings. Many of the other jobs were done at night using a gas light and head torches!
With some counterweights removed, the mirror could be examined more closely. The cell does not slide out from the back as in some scopes, so it was clear the mirror would need to be lifted from the front and manoeuvred out through the gap in the tube.
It is clear from this view just how bad the coating had got! The salty air in this part of the world doesn’t help matters. If the writing found on the reverse of the mirror is to be believed, the last time it was recoated was probably 12-13 years ago. Note the clip holding the mirror (one of four); it has quite a generous overlap above the surface. There are also lateral holding screws. One is just visible.
Ian was the brave soul who removed it! His photo here shows evidence of the surface degradation. There were no signs of any damage though
At 15” diameter and 3” thickness, this is a very heavy and impressive piece of glass.
The plywood mirror cell has three floating panels providing nine support points in total. This is quite remarkable for such a thick mirror comparing it to today’s standards.
This gives some indication of the quality of design and manufacture of the scope - very substantial and stable in every respect.
The mirror was packed in a specially made wooden crate. The box was lined with carpet and the mirror covered with tissue. The whole space was packed with bubble-wrap, providing about 3” of cushioning all round. One of the corners was used to hold the secondary mirror. The lid was screwed down and the sent to Galvoptics so the mirrors could be re-coated.
