On Sunday October 27th 2013, 6 members of the Kingston Astronomy Club got together to remove, clean and replace the two optical mirrors in the 16″ telescope.
The entire process took about 4 hours (mainly because we took a tea break in the middle while the mirrors were soaking).
We documented the process with a video camera (whose battery died about an hour in) and a lot of photographs. We learned how the mirror came out of the cell (the mirror holder) and more importantly, how it went back together again!!
A lot of the lightly adhering surface crud came off but there was also a lot of heavily adhering crud that was reduced but still remains. Lastly there seemed to be a lot of coating erosion/corrosion. To the point that the mirror will have to be recoated in the mid-range future (probably the summer of 2014).
Monday night promises to be clear and cold so the optics (primary and secondary mirrors) can be collimated and some more baseline images taken to see if the focusing has improved compared to the previous baseline images.
The cleaning details:
We set up a shade tent, two 2×4 tables, a tablecloth, a plastic bin to use as a bath tub and a lot of reverse osmosis (RO) water.
All of the parts coming off had seperate bins to put pieces into and all bits were marked with alignment and numbers of go back together the same way.
The camera and filter wheel came off first, followed by the primary mirror cell.
We then took out the mirror out of the cell and immersed it in the tub with warmed RO water and a bit of non abrasive detergent dissolved in.
A lot of sloshing back and forth and then a 30 minute soak followed.
In the meantime, the secondary mirror came off easily and also went into the tub.
30 minutes later we looked at the smaller secondary first, gently dragged with no pressure, cotton balls across the surface radially inside to outside a couple of times around, then rinsed with more RO water and then another rinse with 70% isopropyl alcohol and then let dry sitting vertical.
The results were good, a lot of the surface crud had come off.
The primary was in worse shape. After a rinse and more water with soap, we went around the entire mirror 2 additional times dragging a cotton ball (a new one for each pass). Again, a lot of lightly adhering surface crud came off but it still looks not great. More alcohol rinses and eventually we decided that was as much as we could do. We suspect the coating itself is showing signs of distress and corrosion.
We think that for any more substantial improvement, the mirror itself will have to be stripped and recoated.