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Equipment Discussions >> Classic Telescopes

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tim53
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Reged: 12/17/04

Loc: Highland Park, CA
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5062547 - 02/08/12 04:10 PM

I still think you got a good deal, and if you learn something about the workings of a C-8 in the process of cleaning and reassembling it, it's an even better deal.

The only thing I'd be concerned about is if the corrector had been broken and replaced with a sheet of plate glass. But it sounds as if the seller wouldn't have been knowledgeable enough to do that, so it's probably unlikely.

Even if the primary and secondary coatings are bad, OWL still has a 50% off deal going that you might want to consider. Then, you could wind up with an essentially "new" orange tube C-8 for about $350. Still a good deal.

-Tim.


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DAVIDG
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Reged: 12/02/04

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Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5062654 - 02/08/12 05:26 PM

Joe,
Don't give up on the motors either. You can take the gear boxes apart either by unsoldering the case or just bending the taps back. A good cleaning and some fresh grease my be all they need.
I fixed a couple of motors this way. I even fixed a gear inside the gear box missing a couple of teeth by pressing it into modeling clay to make a mold, turning the gear in the mold so the missing teeth were positioned were the impression had some good teeth and using a couple of drops of epoxy to form new ones. That motor is a very rare one with a built in clutch on the output shaft and used on my Jaegers mount. It has been working without problems for a couple of years now.
My C-14 spent a good part of it's life outside and the corrector had green slim growing half way up it and it cleaned up perfectly. Here is a link to the old C-8 I'm restoring now and it was also in pretty bad shape when I first got it and cleaned up very well. old C-8

- Dave


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: tim53]
      #5062752 - 02/08/12 06:37 PM

This morning under bright sun, I saw on the corrector some of the greenish/purplish reflections that one expects of the C8's "Special Coatings," which are antireflectives. Furthermore, if anyone had replaced the original corrector with plate glass, would they, or how would they, have so perfectly matched the salty coating of the new glass to the rest of the scope? I have the original corrector.

After I get the scope working, as I assume I shall, I'll evaluate it, and possibly have OWL recoat the mirrors. I do not expect they will be especially damaged, but how much reflectivity would they have lost just due to time? These mirrors are thirty-five years old. To pull a number out of thin air, if they were now only 67% reflective, then my C8 would perform more like a C6. That would be a good reason to recoat the mirrors.

What about the RA axis? For $30 at Astro Parts Outlet, I could buy the parts to fix the manual slow motion control, and live without motors in my current mount, which is okay with me. I could also spend $150 to replace the entire housing with gears and motors, or $225 for a housing complete with Byers worm gear drive. Anyone know a less costly source? Or, reading a post that arrived while I was writing this, I may be able to fix the motors I already have!

How much is that Brandon worth? Total potential investment in C8 could then be said to be:

$250 - (value of Brandon and other accessories) + ($50 in various bolts and parts) + (cost to recoat mirrors) + (cost of new motors)

Those last two expenses would be nil if I chose not to incur them. Then again, if the optics were excellent, a fully restored C8 would be cool, and a far better teacher than the new ones with computerized mounts!


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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5065065 - 02/10/12 08:33 AM

With special thanks to Lady Cepleur, the obvious next step is to reverse the corrector, even prior to cleaning, to test whether that allowed the telescope to be brought into focus. Trouble is, the corrector can not currently be removed, because the Allen bolts attaching it to the scope are frozen. Might anyone know any tricks for loosening them?

There may be a special problem due to the salt water damage. I've been reading about cleaning salt water deposits from glass and metal. (Lots of information is available in the context of cleaning salt water aquariums.) Sea salt is not as innocent as table salt. It contains minerals that harden remarkably solid. Fortunately, they are soluble in white vinegar, so one solution would be to soak the corrector end of the tube in a tub of vinegar overnight. I'm thinking this would do no further harm than the salt water already has, and that, eventually, the entire scope may need a long soak in vinegar. Can anyone think of a better idea, or a good reason not to do this?


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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: tim53]
      #5070213 - 02/13/12 10:32 AM

Quote:

I still think you got a good deal, and if you learn something about the workings of a C-8 in the process of cleaning and reassembling it, it's an even better deal.




Thanks, Tim. I found another thread of yours showing your beautiful reconditioning of a scope with worse beginnings, and was truly inspired. I'm thinking now, "Yeah; if Tim can fix that, a little penetrating oil, some time, and elbow grease should restore mine." May required a little more cash, but it will be worthwhile in the end.


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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5070221 - 02/13/12 10:38 AM

This thread segued to the Cats & Casses Forum. A specific question there about loosening frozen bolts near the corrector generated a great deal of input. I will continue here in Classics as the restoration proceeds.

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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5072205 - 02/14/12 02:16 PM

Progress! The question at Cats & Casses about removing the frozen bolts without breaking the corrector morphed into ideas on how, finally, to get the scope to focus. The corrector was not reversed, but the secondary housing had been floppy, distorting the light path. The scope now yields impressive close-up views of objects over a mile-and-a-half away across the lake.

I had also asked a question on the Eyepieces Forum that lead to a discussion about dating not just the Brandon that came with the C8, but those of other members as well. Mine appears to be among the original Vernonscopes from the early to mid 1960s, the third model produced. I do not believe it sold with the scope from the factory, but am glad it somehow found its way into my kit.

Looking around old Classics posts, I've seen far worse C8s successfully restored. With mine now focusing, I am confident mine can be restored, too, and will post its progress here.


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5076727 - 02/17/12 10:15 AM

A daring friend and I are preparing to disassemble the C8 for cleaning. I know the importance of marking the corrector, to assure that it is reassembled in its exact, original orientation. What about the primary mirror? Will it attach in only one orientation, or can it rotate if we are not careful?

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Brian RisleyModerator
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Reged: 09/04/06

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Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5077145 - 02/17/12 02:05 PM

It should be secured to its mounting plate. The focus shaft allows it to only go in one way. The mirror should have RTV around the central hole, so even removing the lock ring should not allow it to move.
Brian


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Brian Risley]
      #5077170 - 02/17/12 02:23 PM

"RTV" -- What's that? On Google, I found a silicone adhesive used for gaskets. Do you mean that, in addition to the locking ring, the mirror is secured with some kind of silicone adhesive? How would I unstick that?!

And, would it mean that, upon reinserting the mirror, I should put a dab of fresh RTV?

I imagine this goo is used to prevent the mirror from shaking around and getting damaged, despite the close tolerances.


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tim53
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Reged: 12/17/04

Loc: Highland Park, CA
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5077181 - 02/17/12 02:28 PM

The RTV was put in to keep the mirror centered. I wouldn't remove it, but see if you can clean the assembly assembled.

-Tim.


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: tim53]
      #5077483 - 02/17/12 06:13 PM

Okay, thanks. So, the RTV is the glue holding the mirror to its carrier in the assembly, as seen at the bottom of the page in a five-year-old article on Astromart by Greg Nowell showing how to disassemble a Schmidt-Cassegrain:

C-8 Mirror Assembly

Getting ahead of myself, if the mirror must be carefully centered on that assembly, what happens if it needs to be recoated? Can an upstart wannabe telescope restorer successfully center a mirror at home?

Edited by Joe Cepleur (02/18/12 05:16 PM)


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Brian RisleyModerator
Carpal Tunnel
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Reged: 09/04/06

Loc: SW Florida
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5078371 - 02/18/12 11:22 AM

Joe,
The RTV is in addition to the metal retaining ring/cork shim that you see. It is between the glass and the shaft and often some leaks around the back and is often visible.
Centering and making sure it is square is a bit of a trick, square can be done if you have a turntable or lathe (That is level) and can spin the mirror assembly. If you point a laser at it, the reflection should not move when you rotate it. There may be a large rubber O-ring underneath that helps keep it centered, but one can also measure from the inside edge of the tube to the mirror edge all the way around. One must also be sure the RTV replacement does not outgas much.

Unless you remove the mirror from the cell assembly, you should not need to worry about the RTV.

You will want to lube the shaft/inside of the mirror focus tube assembly. This makes the focus smooth and helps with mirror flop. Again, use a lube that will not outgas much. Some recommend the Corning High Vacuum stuff, others say the SuperLube grease (not the spray) and other say a Mobil1 grease. You want something that won't run at higher temps or solidify at lower temps.

Brian


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Brian Risley]
      #5078471 - 02/18/12 12:36 PM

Centering the mirror sounds tricky. I've written to Optic Wave Labs asking whether I could ship the mirror on its base, and have them reattach and center it after coating.

Looking at the mirror while its still in the tube, I'm seeing many tiny areas that look scratched. Perhaps the salt did that, or a crude prior cleaning. I'm sure the scope could work as is with the mirrors only cleaned, but looking at the partially peeled coating of the secondary, it couldn't hurt to get them restored to better than new condition -- especially at half price.

The DOW reached 13,000. Gotta hurry, we'll all hope, before it reaches 14,000, and OWL's price for recoating doubles back to normal!

Next vexing bit o'foresight: I understand about marking the corrector and tube with tape, to assure proper alignment upon reassembly. Trouble is, cleaning the mirror is likely to remove the tape. Any solution? I had thought of using duct tape or some other waterproof tape, but only at the very edge, the part covered by the corrector's retaining ring, so any residue would not show cosmetically or alter the image.


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Brian RisleyModerator
Carpal Tunnel
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Reged: 09/04/06

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Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5078777 - 02/18/12 03:56 PM

There should be alignment lines (usually blue) on the back of the secondary and the primary that will allow you to get them back into orientation with the corrector serial #. The primary mark should be located opposite the focus shaft. This ties the optics to the back cell.
Brian


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Brian Risley]
      #5079655 - 02/19/12 07:06 AM

Quote:

alignment lines (usually blue) on the back of the secondary and the primary that will allow you to get them back into orientation with the corrector serial #




I can picture that, thanks. How precisely must they be aligned? It should be fairly easy to get the secondary pretty close to perfect with the corrector, because they bolt together. What about aligning that assembly with the primary? Obviously, a careless 50° out alignment would hurt, yet eyeballing components that are stuffed into a tube over a foot apart may be difficult to get perfect. I've read that, in collimating this scope, a fraction of a turn of a collimating screw could make a big difference. Is the alignment of these components as touchy? Does it need to be perfect, or just close enough?

Hard to believe that, yes, somehow I'll fix this scope, and then I'll be the one answering these questions for others in the future!


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cheepnis
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Reged: 02/16/08

Loc: Columbus, OH
Re: The Plot Thickens: Fixing a Salt-Encrusted C8 new [Re: Joe Cepleur]
      #5080800 - 02/19/12 06:25 PM

Great links in this thread, I'm making a bookmarks folder for all this good info.

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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
Re: Inspecting a C8 Prior to Purchase new [Re: Geo.]
      #5081586 - 02/20/12 08:42 AM

Rereading this thread to consolidate all I have learned, I am struck by George's comment from the first page:

Quote:

Only a few orange Super C8s were StarBright, so the coatings of this C8 will be either standard Al SiO2 on the mirrors and perhaps antirefective on the corrector ("Special Coatings"). Starbright is noticably brighter than the standard coatings. So the light thruput of an orange C8 is about the same as a C6 XLT.




Margarita has special coatings... Sorry; better explain that. Amicus Sidera asked:

Quote:

...have you considered christening that salt-encrusted C8 as "The margarita Scope"?




I like that. I don't usually name objects other than boats, but in this case, we'll call her "Margarita!"

Margarita has special coatings, but it sounds as though to get not only the resolution, but also the full brightness and reach of the 8" mirror, I should ship the mirrors off to OWL before the DOW hits 14,000 again, regardless of the condition they appear to be in after cleaning. I mean, it would be awful if the DOW rose so high, but I were behind the times, wouldn't it? Imagine the horror if, after all the work to fix this thing, I could afford to buy a new one, or a fully restored classic, instead! Horrors! Whatever the economy, it makes sense to spend a hundred bucks to effectively gain two inches of aperture.


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Restoring a C8 After Purchase -- Update new [Re: Joe Cepleur]
      #5133621 - 03/21/12 12:57 PM

Hard to believe a month has passed since I last posted about Margarita. Four stars had to align before I was able to proceed.

First, in a bout of buyer's remorse, I began to wonder whether she were a financial boondoggle after all. Looking ahead to the cost of recoating the mirrors and possibly buying a Byers worm drive, might it have been fiscally sounder to simply rejoice in the Brandon, ortho, and even the Kelners that came with the scope, sell the rest for parts (the tripod and wedge would each eBay for about $100), and then buy another old orange tube that was ready for use? I watched prices on eBay for a while, and decided, "maybe, maybe not." Then there was the trouble beyond cost. If I sold what I had, I'd also lose the experience of restoring a classic, which, while a fun pain, was priceless.

Then, after I found a way to brace the secondary prior to disassembling the scope, my club's optician collimated the optics. They won't hold until the secondary support is properly fixed, but it became evident that, yes, under the salt, Margarita is a perfectly fine C8! No such guarantees if I sell her for another. He is also a wizard of mechanics. We're going to add a manual slo-mo worm gear to the polar axis. This slo-mo will be better than the stock spur gear version anyway.

Finally, winter has come to an early end, so I have been able to turn the running water back on in the house. Been lugging washing, flushing, and drinking water all winter, and heck if I were going to drag enough extra to clean a telescope! Remember, it's not just the mirrors that need a rinse, but the whole salty mess. Now when I get her apart, into a padded sink she'll go, for a bath of the finest running well water, followed by a carry-in rinse of distilled.

The end of winter also means I can work on her outside, which is important with chemical sensitivities in the household. Figuring I could always return to PB Blaster, I bought a DuPont Teflon Penetrant instead. It's low odor, and it is sold with its own eyedropperish bottle. No need to transfer a spray can of PB Blaster into an eyedropper before I began. The penetrant has already opened all of the bolts except those on the corrector, but those have been soaking for a few days, so I'll try again soon.

Never would have anticipated that I would have become a convert to Cassagrains, but I'm pretty excited. It won't be as fine optically as Caveman's 9-inch, unobstructed refractor, but in exchange for acceptable optical trade-offs, I'll get a seven-and-a-half foot long telescope that magically fits in my car and carries outside easily, and a matching seven-foot tall, two-hundred pound pier that weighs nothing and nestles into the trunk. How cool is that? And, it'll have classic cache to match its optical prowess, making it in that regard better than new!

I'm amazed the more I study the C8. It's really a pretty simple device, if one made to exacting standards through a complex manufacturing process.

I'm sure you've all heard about the loss of Tom Johnson, founder of Celestron, whose solution to the problem of making corrector plates inexpensively caused the Cassagrain revolution. This one's for him!


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PhilCo126
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Reged: 01/14/05

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Re: Restoring a C8 After Purchase -- Update new [Re: Joe Cepleur]
      #5137006 - 03/23/12 11:46 AM

Looks like a " restoration project " scope

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