Uncle Rod's Astro Blog

It’s a good thing this is a family friendly blog, muchachos, or that title above would have been a lot nastier. As most of y’all know, when it comes to SCTs I’ve always been a Celestron man. Have been for many a long year. Will that change? I don’t know, but I’m plenty put out at them right now. The way I feel at the moment, if I were to buy another SCT it would have a blue tube, or would at least be a used Celestron from before the Synta era.

Until now, the Celestron scopes I’ve owned have just kept on keeping on year after year after year with only the most minor of minor maintenance needed—like occasional cleaning of the inside surface of their corrector plates. So, imagine my surprise and anger when I discovered my beloved Edge 800, Mrs. Emma Peel, had a serious problem thanks to a mistake made at the factory and would require major maintenance after only seven years of ownership.

I’m not sure exactly when Emma’s problem began to make itself known, but I first noticed it many months back:  a shiny inch-wide streak on the inside of the tube running from almost the corrector to almost the primary mirror. I assumed this was from dew that had condensed and slightly discolored the inside surface of the tube. I figured it would eventually disappear and wasn’t a big deal one way or the other.

Then, when I had the scope out the other day getting ready for the start of the New Herschel Project, I noticed the streak was still there and more prominent than ever. I got worried then. I was afraid that, rather than being a stain left by condensation, it might be lubricant from the exterior of the baffle tube or from the focuser that had liquified and run down the tube. That could be a problem, since if the tube got even somewhat hot, that lubricant might begin to vaporize and be deposited on corrector or—worse—primary mirror. I resolved to open Emma up and do some cleaning. I hadn’t cleaned the inside of her corrector since I bought the scope in the spring of 2013, so it was about time for that anyway.

OK…so time to pull Emma’s corrector. Early one morning, I prepared a place as I always do with plenty of towels for cushioning in the event the lens gets away from me. I also put a folded towel under the corrector assembly so the tube pointed up a little so the corrector plate wouldn't be likely to fall out when the retaining ring was removed. I thought this would be pretty standard stuff. It would certainly not be the first time I’d torn an SCT down to parade rest. A colleague at the university once timed me to see how quickly I could get a corrector plate off and back on on one of the physics department’s scopes (a student had somehow managed to drop an eyepiece cap down the rear port). I set a personal record of seven minutes that time.

I intended to take my time on this one, though. It was somewhat new territory in at least one regard. In the past, Celestron scopes have used little shims around the periphery of the corrector to properly center it—the center position with regard to the primary may not be centered on the corrector mounting on the tube due to mechanical variances. These shims in the past have been little pieces of cork, or, more often, folded paper…pieces of Post-it notes in recent times.

When you put the scope back together, you naturally want to get the corrector properly re-centered in the interests of best optical performance. It was not that hard to use a pencil on the lip of the tube to mark where the shims went, but, yeah, the little pieces of paper deal was kinda fussy and silly. The Edges abandon that for nylon hex screws around the corrector periphery. They thread through the “ring” on the end of the tube, the corrector assembly, and adjust centering. I think it’s a pretty good system. If Celestron isn’t using this on all their tubes, they should be.

I had a standard Celestron OTA here for a review a while back, but li’l old me can’t remember if the nylon screws were used on it or not. Frankly, a lot of things that happened in the year or two before my accident in the late winter of 2019 are strangely fuzzy in my memory now. Go figure. Anyhow, maybe one of you, dear readers, can answer that question for me.

So, first order of business was backing out those screws half a turn using a 2mm hex wrench. If/when you follow in Unk’s footsteps, mark the first one you loosen so you don’t lose track. That done, the next step in Edge corrector pulling is the same as it ever was.

Firstly, remove the screws that hold the plastic retaining ring against the corrector. Unk put all them screws in a little paper bowl…small screws love to run away and hide on the floor of Unk’s radio shack, which is also his Workshop of the Telescopes. The plastic retaining ring is now accompanied by some foam-like gasket material. Guess that’s OK, though I don’t see much need.

Before proceeding, use a soft pencil or marker to mark the rotational position of the corrector. Celestron no longer engraves a serial number on the corrector periphery, so you can’t use that for indexing anymore. Retainer off and put in a safe place, I removed the scope’s Faststar secondary and put it in a safe place too. “Welp, now all I gotta do is pull the corrector out.”

Alas, Mr. Corrector didn’t want to budge. It’s not unusual for correctors to get “welded” to the corrector assembly by the passage of time. A little prying with a jeweler’s screwdriver always frees them, though. However, I could tell immediately that wouldn’t work this time. The feel told me the corrector was still firmly, and I do mean firmly, seated in place. What to do? What I always do in these situations. I stopped, trotted back to the house, made myself another cup of java on the fricking Keurig, and considered the situation.

Somewhat more awake, and equipped with my glasses, I took a second look at the corrector. “Oh, Celestron, you &%$*!!@ idiots!” My now clearer eyes revealed four spots of RTV where the corrector had been glued in place. Why would they do such a thing? Search me. The Nylon screws and the retainer are more than enough to hold the lens in place. And surely, they are aware the corrector will have to be removed sooner rather than later for corrector cleaning or some other reason—like weird streaks of something on the tube interior. What were they thinking?

Once Unk calmed down a little, a boxcutter retrieved from the shack’s bench made short work of that dagnabbed RTV, and the corrector was off and placed in a safe spot. Your old uncle wasn’t quite fuming now. But he would shortly be fuming again in epic proportions. To the tune of one of his classic melt-downs.

“Hokay, let’s get that funny-looking streak cleaned up.” I thought I’d probably better start gently with just a damp paper towel—damp with tap water. I scrubbed a little. “Funny. Doesn’t seem to be coming off. Seems to be…getting worse.” One look at the towel told the tale:  It was black with stuff that seemed to have the consistency of lamp black—if you’re old enough to remember what that was. “What the—?!”

What was going on was all too obvious. The paint on the interior of the tube was coming off with gentle scrubbing. The streak hadn’t been some contaminant; it had been the paint failing. Why? Whoever ran the sprayer through the interior of the aluminum tubing to paint it black at the factory in the PRC hadn’t properly cleaned the aluminum first. A little googling later on the freaking Internet soon showed I am not the only person to have experienced this. And that those people I read about who’d reported the problem to Celestron all received the same response, “First we’ve heard of that problem.” Uh-huh.

When Unk recovered from a meltdown wherein he assumed the character of a small, emotionally disturbed child, it was time to consider what to do about Emma. Ship her to Celestron? Nope. Not only was I not exactly in the mood to deal with those suckers, I didn’t want to pay shipping—even if only one way if Celestron agreed to that. And with the Covid 19 virus still running rampant, who knew how long they'd hang onto the scope? I didn’t want to devise a shipping container, either (after years of ownership I didn’t think I needed to hang onto the box the OTA came in any longer). Finally, I didn’t want to subject my telescope to the tender mercies of UPS. 

What I’d have to do was clean as much of the old paint off as possible and repaint the bad area.

First thing to do was mask and glove up and visit Home Depot. A few minutes turned up a small can of high-quality flat black paint. Latex paint. I was loath to use some kind of oil paint with its associated fumes on the scope’s semi-sealed interior. Oh, and a good quality, small brush. Unless I wanted to pull the primary and do a really complete tear down, which I didn’t, brushing would be the only way. Even a small roller would be likely to generate tiny drops of paint and contaminate the primary.

The actual job was not as bad as I’d feared. I cleaned off as much paint as I could in the obviously affected area (my damp cloth easily got me down to bare metal).  That done, I brushed on two light coats of paint. The result looked pretty good. Now, brushed-on paint will never be quite as even or pretty looking as a spray job, but maybe you don’t want it to be so even and pretty. A little texture can help reduce scattered light. One thing was sure:  my paint was a lot blacker than what Celestron used, which was more like “medium gray.”

While the paint was drying, I did some more looking around the OTA. “Well…there’s another spot. Oh, and one over there too. It became obvious the entire tube interior had to be repainted. Which I did, exercising care not to get any paint on the primary mirror. It turned out rather well, I think. I’m just hoping I cleaned well enough in the worst spots to get the paint to adhere, and that in the other places the latex will act as a sealer. Time will tell, I reckon. Anyhow, I left the paint to dry overnight before proceeding to reassembly.

Painting done; I cleaned the interior surface of the corrector plate using my time-honored method; one I’ve been using for well over 30 years. What’s required is a box of Kleenex, the unscented and un-lotioned variety; a can of canned air; and a bottle of original (blue) Windex. While some folks worry that something in Windex might somehow harm the optical coatings on a corrector, that has certainly not been the case with any of the many, many telescopes I’ve used it on over the years. Remember, lens coatings are tough, anyway, very tough; they are entirely different from the coatings on first-surface mirrors.

Anyhoo, what I do is blow any dust off the lens’ surface using the canned air. Like Windex, canned air will not hurt your corrector. Do hold the can upright and keep it about 18-inches away. Next, I spritz a Kleenex with a little Windex and swab gently starting at the secondary mount and proceeding outwards, changing tissues every once in a while. Finally, I dry the corrector with fresh, clean tissues. To finish up, I use the canned air to get rid of any lint left by the Kleenex. Again, this method will not hurt your lens, and Windex does a better—far better—job than any lens cleaning fluid I’ve ever used.

Next morning, it was time to get poor Emma back together and off the operating table. No real surprises. The little studs Celestron places around the corrector periphery to engage the dust cap make it kind of a pain to get the retainer back on—you have to bend it gently and slip it into place. That done, retighten the centering screws by the amount you loosened them, replace the screws in the retainer (just snug only), and you are done.

As you can see, the girl was back to being her usual photogenic self. And I was pretty sure she’d get a clean bill of health under the stars once I got some of those increasingly rare clear skies. While Tropical Storm Cristobal didn’t go straight over our heads, it came close enough to dump tons of rain.

The denouement, when the evil old clouds finally scudded off for a couple of evenings? I got Emma out for both visual and video observing (which you will read about next week) and she performed just as well as she ever has. She was even still in collimation. The paint job is holding up despite a couple of days under a Telegizmos cover in the heat and humidity of the backyard, so all is well for now and Unk has his fingers and toes crossed.

So, anyhow, what’s my takeaway? I’m still mad at Celestron. I didn’t go out and buy an Edge 800 the day they hit the streets, so this wasn’t a case of early adopter syndrome. And painting the interior of the tube should have been something they could have done successfully no matter what the design of the scope.

But that’s just the way the cookie crumbles. I plan to stop stewing about it and get out under the stars with Mrs. Peel as often as I can in the service of the New Herschel Project. That’s what our magnificent obsession is about, not worrying over the depredations of telescope companies.

Book Plug Department

This time, that plug is for my own book, the 2nd Edition of Choosing and Using a New CAT. I am as happy with this one as I am with anything I've written, and hope you will be too. It is now available from Amazon in both print and Kindle editions.