Ed T decided to use the old orange tube C8 from the GBO, a bequest from Mr Litovitz. He lugged the monster while I guided him through doors and over steps. As he took a break, I humped it the rest of the way to the observing pad.The old girl operates on AC so we put her very near the centre post GFCI. I assumed the fork tines were to point north.
Ed found a 1¼" diagonal from the eyepiece cabinet (the one used the evening before with the MallinCam). He then started to track down some eyepieces. I confessed that I did not know if there were any specifically for this 'scope. I directed Ed to the storage closet but all he found was a box for the finder scope with the donor's name. I offered my eyepieces and 2" visual back and mirror. Initially, Ed declined, opting to use some of the GBO oculars.
He fine tuned the mount, aligned a Telrad, and learned the general operation of the 'scope. We verified the clock drive was working.
As it got dark, Ed reported that the light in the mount was distracting. I had noticed the orange (neon?) bulb inside the housing early. I wondered if a plate was missing. We rummaged up some black electrician's tape and covered the opening. It resisted sticking, in the humidity, but I think it worked out well, overall.
Later, Ed remarked that the old cat seemed out of alignment. He wondered if it needed collimation. We looked through different eyepieces and could see coma. Very distracting. It seemed worse at low power.
I admitted that I had only done collimation a couple of times with my SCT and I was rusty. But I offered to find some instructions on how to do it. I charged Ed with finding the tiny Allan key for the 3 adjustment screws on the secondary while I began a search... After a bit of digging, and a moment of inspiration, I found, on one of my USB memory thumb key stick drive flash things, a general C8 document which included adjustment notes. Woot! I rushed to the observing pad, netbook in hand, red cel firmly attached to the LCD, PDF on screen.
It was dark.
From memory, I reviewed the overall plan. It was coming back to me now... I thought it appropriate that it be done by 2 people: one could stay at the eyepiece while the other adjusted. We would switch between inner and outer focus watching for concentric diffraction rings. I remembered that we needed to select a bright star and then dimmer star and then progressively fainter stars to complete an optimal collimation. Then I told Ed we should use a star near zenith. Oh. Oh. Fork mount. Right. Looking at objects overhead might be a back-breaker. Would the mirror and eyepiece fit? Oh! Right. The mirror. Suddenly, I remembered that it was recommended that the mirror diagonal be removed during collimation, so to eliminate any possible issues or problems... with that element in the optical... path...
The mirror!
What if the mirror was causing the coma problem?!
I suggested to Ed that before we start any collimation that we switch the mirror. I pulled the old Celestron star diagonal (in metal body) from my eyepiece case. "Blake," Ed noted, "you're the only person I know with lights inside their eyepiece case." Surely, I'm not the only one with little red LEDs and a tilt switch, surely! We slotted in the old diagonal. And despite some chips out the corner of the mirror, it offered a crisp, clear, coma-free view.
We agreed that a mirror diagonal with a chintzy plastic cover was not likely going to be good quality and not necessarily in good alignment. I wondered if the mirror itself could be collimated. It has 4 little screws (ur, 3, one's missing) on the back of the plastic case. Merits a look inside. Or, we should just get a replacement... Hmm. This, again, was in service with the MallinCam the night before. We wondered how much it might have degraded the view...
Anyway, I was happy. It was kinda cool working on the vintage SCT. It was fun mixing in my parts to make it work. Ed was happy. He got some mileage out of the classic Celestron. Got some observing in after I had convinced him to stay one more night.
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So, some issues with the C8:
- earlier in the evening, we had noted the ocular was missing from the finder scope
- mirror diagonal is in bad shape; needs repair or replacement
- find eyepieces, if there were any
- if we're going to replace the mirror, why not upgrade to 2" visual back and diagonal?; then we can tap into full range of GBO eyepieces
- add a plate / plaque with the donor's name
- the RA (if I remember correctly) knob is very stiff, jumps; lubrication needed? tension adjustment?
- find missing plate or cover
§
C8 fork-mount photo by wikipedia user (and photographer) Opoterser.
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