Saturday, December 27, 2008

cleaned mirror, twice

I wanted to collimate Mom's Newtonian telescope. The images didn't look as crisp to me the last time I used it (back in the summer? my birthday?). I suspected it needed a tune up...

With Tectron tools (long sight tube, cheshire, and autocollimator) and Kendrick laser collimator—on loan from Guy—I was ready to do a good job on the old Edmund Scientific.

But it became clear to me that to use all these tools properly, I needed to know where the centre of the primary mirror was. And that would require removing it. From the OTA. And from the cell. And if I was going to do all that, I might as well clean it.


Once removed and examined closely, we were all (Donna, Steve, Mom, and me) left with the impression that it was filthy! Cleaning was overdue!


I reviewed my Newtonian cleaning notes. And made a shopping list. Mom headed into town in the morning and picked up 8 litres of distilled water and 2 boxes of large sterile gauze pads (presumably cotton). I steeled myself.

I removed the mirror from the cell. The 3 edge clamps came off easily. But the mirror was stuck in the cell. With some force, I was able to separate the two pieces. A rubber donut on the back of the mirror I was able to separate from another donut affixed to the cell frame. The cell donut was torn in the process but not damaged severely.

Mom has a suspended-style dishrack in one of the kitchen sinks. I rested the 6" Pyrex mirror in the dishrack such that it was inclined at a 45° angle. Then I used Mom's kitchen sink retractable spray nozzle to give the mirror a good soaking. Sadly, it seemed, none of the debris was washed away in this process. Oh boy. How badly stuck is this stuff?

Next I placed the mirror on the counter and filled the parabola with distilled water. I placed a new sterile pad in the centre of the mirror and let it soak up the water. Then, by gently tugged on one of the pad's corners, I pulled the pad off the mirror. I was thrilled to see a cleaner surface in the pad's wake. I filled the mirror again. This time, I tugged the corner of a new pad in a swirling pattern, letting the large pad sweep from the mirror's centre to edge. I did a couple of loops and tossed out the pad. Wow. Already it looked better. I repeated this about 10 times. And I reviewed my notes. Oops!

The notes said to use soap-water for this process as opposed to distilled. OK. Let's get a cleaning agent on it. So I filled the other basin with tap water and, as directed, put in one single drop of dishwashing liquid. I used this water with a couple of more gauze pads. The mirror looked much better than when I started!

Rinse cycle! Back into the elevated dish rack and I poured about 6 litres of distilled over the mirror to ensure it was totally clear.

Back to the counter, I gently blotted up the water with a clean pad. Wow. I should have taken before and after pictures...

I showed the mirror to Mom.

Curiously, looking straight down on the mirror, you can see a mottled pattern. I wonder if it is something deeper in the aluminum coating. Oxidation? Looking obliquely, the mirror looked significantly better than before. Oh well, regardless of the coating, the overall state was much improved.

I set the mirror down in the kitchen and began the steps of making a template so to find the centre of the mirror. I heard Mom in the kitchen puttering about.

When I returned to the kitchen a few moments later, I saw 3 large smudges on the mirror. It looked horrible. "What happened?!" I gasped.

Mom said something splattered and fell on the mirror. She had tried to wipe it clean, perhaps with a dishtowel. I was horrified. "Why didn't you tell me?!"

I didn't see any scratches but I blurted out, "You might have destroyed it." A bit severe perhaps but I was just stunned. My heart was sinking but I was trying to shore up. I was truly hoping there was no damage.

"I'll have to clean it again." And I set about repeating the process while Mom retrieved more cotton pads. I washed with tap water, went immediately to the soap water, and was relieved to see the mirror coming clean, and did the final rinse (from the remaining distilled water jug). After blotting, I looked very closely at the mirror. I don't think there were any scratches made. If there are, they are microscopic; nothing I could see naked eye.

I was relieved but still upset. Perhaps it was good that I needed to retire to the garage to reinstall the mirror. After which I collimated...

Mom was pretty quiet when I returned. She must be upset too.

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