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HomeAstrophotography“Celestron Screws Up” or “Poor Emma”

“Celestron Screws Up” or “Poor Emma”

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.
Prepare a good, safe place to pull the corrector.
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
Mark the cetering screw you begin with so you don’t lose track.
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
. 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.
Removing the retaining ring.
“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
What was going on was all too obvious. The paint
on the interior of the tube was coming off with gentle scrubbing.
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 crux of the problem–after some gentle scrubbing.
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 good as new? I hope so.
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
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. 

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