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Equipment Discussions >> Classic Telescopes

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Brian RisleyModerator
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Re: Fixing a C8 After Purchase new [Re: Joe Cepleur]
      #5059608 - 02/07/12 01:05 AM

Joe, Have you downloaded the 1975 manual for the C-5/C-8 from Company 7's Site. Later color manual here!

(This is an older manual, but does show the dec slow mo assembly very nicely.)

There is only one dec knob on the OT's. The other side is for adjusting it. Release the nut and adjust the pivot so it moves freely but does not move in/out, then tighten nut.

Measure the width of the focus knob needed with calipers.
There aren't any general supplies but you may find one at Astro Parts Outlet.

(In all honesty, once you get a chance to check the optics, I would ditch the fork and go GEM or pickup a used one that is in good shape. You will spend more looking for motors/gears. (The gears can be obtained from Boston Gear, but attaching them to a motor shift is a real PITA!) I have replaced the RA slow mo knob on one of mine, but I only needed the gear and shaft, had the knob.
The visible gear is for the motors only! There is another gear under the plate (held in place by the central 4 screws). The 3 outer screws keep the gears together. Don't remove them as there is also a large flat spring and the RA setting circle to deal with.
This is the only way to go in and replace the RA knob shaft!
When you do, you will find either a metal or nylon piece directly under the RA Lock screw. (Nylon is better!)
Motors are not off the shelf, they are 1 RPH Counter Clockwise and you would probably have to fit the correct gear on it. When doing that, it is very easy to damage the internal gearbox setup too!
(I completely rebuilt my 71/72 and have had my 80 apart, so I say this from experience!)

As for the optics, I would lookup one of the disassembly instruction sites and remove the corrector ring and look on the edge of the corrector for the serial number. (It should be on the side directly opposite the focuser! You will need to then remove the secondary (center screw holds the mirror in, tighten the 2 sections of the holder (it screws on to the corrector with the inner baffle. Once positioned, you can replace the secondary, look for a line across the back of the holder/mirror or on the side of the mirror. This line/mark should line up with the middle of the serial number on the corrector.
(The serial number is very hard to see, you may need a magnifying glass. Look for a mark on the side of the corrector, it should be there with the serial number.)
If you can't find a serial number, then it is possible that the corrector was broken and replaced with glass! That could explain a very fuzzy image!
Hopefully that is not the case!
They used to sell no tools knob sets for the tripod/wedge screws, but not sure if any are available now. You can purchase your own. The screws to hold the wedge threaded down into the tripod. Celestron used allen head screws for a long time. Many people replaced them with other screws that they could use with a wrench and not worry about the head size.
(I can probably disassemble that thing blindfolded, I did it enough with my older one when rebuilding it!)

I think Tim is starting to get that way working on his early one!

Brian


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Brian RisleyModerator
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Reged: 09/04/06

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Re: Fixing a C8 After Purchase new [Re: Brian Risley]
      #5059611 - 02/07/12 01:09 AM

If it is the stackable counterweights (round with threaded shaft on one side, threaded hole on the other) you remove the screws located in the center top/bottom of the front cell. The 10-24 threads can then take the counterweights.
If it is a bar set, then the bar mounts on the front via the same hole and there will be 2 screws in the back to hold the support.
Brian


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Brian RisleyModerator
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Re: Fixing a C8 After Purchase new [Re: Brian Risley]
      #5059614 - 02/07/12 01:12 AM

The serial number is on the edge of the top side of the corrector, not on the thin edge. Think fine print size and possibly not easily seen straight on. Use a light at an angle.
Brian


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sgorton99
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Re: Fixing a C8 After Purchase new [Re: Brian Risley]
      #5059802 - 02/07/12 07:03 AM

Price wise I think you did fine. Can you post of pick of the EPs? The Brandon may go a ways toward that $250 total...

Steve


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Joe Cepleur
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Re: Fixing a C8 After Purchase new [Re: sgorton99]
      #5059864 - 02/07/12 08:09 AM

Quote:

Price wise I think you did fine. Can you post of pick of the EPs? The Brandon may go a ways toward that $250 total...




Woa! Sounds like I got lucky! I wanted the Brandon because the optician at our club always talks about them, but I've never seen one until now. Company Seven's Web site has a set of maybe five Brandons for about $1,000. Had no idea mine was that valuable!

There are pictures of all the oculars in the earlier pages of this thread.


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Joe Cepleur
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Loc: Dark North Woods
Re: Fixing a C8 After Purchase new [Re: Brian Risley]
      #5059888 - 02/07/12 08:29 AM

Thanks, Brian, for all the details about motors, gears, and knobs. Pictures would help. I'll download the manuals and look for a schematic, or perhaps find photos online.

It's probably good, practical advice to ditch the fork mount for a GEM, but the fork is original and exudes cachet. My club has a spare GEM, and I could use the original tripod, but might it also be possible to keep the fork mount, fix the R.A. slo-mo knob, and not bother with the motors? That would be fine for visual astronomy. One less battery to lug, and silent.

I don't follow about the R.A. axis's visible gear with three screws holding another, larger, hidden gear. The hidden gear works the manual slo-mo? You warn not to remove the visible gear, because of the setting circle's spring underneath. Will it be necessary to remove it anyway in order to fix the slo-mo?

Another possibility: Maybe the parts dealer would have a complete, functioning motor with housing, maybe even a Byers with worm gears.

Edited by Joe Cepleur (02/07/12 09:06 AM)


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Brian RisleyModerator
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Re: Fixing a C8 After Purchase new [Re: Joe Cepleur]
      #5059988 - 02/07/12 09:50 AM

The inner ring held by 4 screws is safe to remove. That will allow the piece with both gears and the setting circles to be removed. (The outer 3 connect the 2 gear plates and sandwich the RA circle/spring.) The spring can be removed, it is just a big piece of spring steel that goes in and gives some resistance to the RA circle so it stays in place in relation to the gears unless you manually rotate it using the 4 black knobs on top.
I really recommend getting a new base if you want to keep the fork style. Some can be had pretty inexpensively. I picked one up for about $35 a while back. You can get the byers or even a later powerstar or celestar fork and use it. The c-8 holes for fork mounting have remained pretty consistent (don't know about the Nexstar/cpc holes).
The celestars could run off a 9v transistor battery, so you can be real portable and still have power.
I think trying to repair it would be more costly, especially if you do ever want it motorized.

To repair the RA knob, you need the gear, a pin and then a knob that can fit below the RA lock knob, so it has to be low profile. (It is basically the same size as the dec knob, but has a smaller shaft hole.)
If you do decide to go that route, I can look through my records for the pin/gear that I ordered (It's been 8 years, so I don't know if I still have the info, but I was keeping it stashed in a box). You still have to secure the gear to the pin, possibly some of the heavy duty loctite.
Brian


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DAVIDG
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Re: Fixing a C8 After Purchase new [Re: Joe Cepleur]
      #5060039 - 02/07/12 10:22 AM

"Upon arriving home, the scope was tested with a known good 32mm Meade Series 4000 Plossl. I believe --I hope!-- it is badly miscollimated. Nothing comes to properly clear focus. the Moon looks fuzzy, as though its craters were covered with white mold. Stars are never pinpoints, but only faint, fuzzy dots."

Even in a bad collimated C-8, the image of a star will come to sharp focus, it won't be round, and will be coma shaped, but it will be sharp. The fuzzy dot appearance and fuzzy Moon sounds like a large amount of spherical aberration. The most likely cause is that the corrector has been flipped in the cell. The fact that the scope has a number of issues caused be the former owner and that the secondary cell is loose adds to the suspicion that corrector maybe backwards in it's cell.

- Dave


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Joe Cepleur
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Re: Fixing a C8 After Purchase new [Re: Brian Risley]
      #5060245 - 02/07/12 12:25 PM

Quote:

If it is the stackable counterweights (round with threaded shaft on one side, threaded hole on the other)...




I have those, thanks. I had not noticed that each had its own shaft and hole. All screwed together for storage, they look as though they are all mounted on a single, long shaft.

Quote:

you remove the screws located in the center top/bottom of the front cell. The 10-24 threads can then take the counterweights.




"Front cell," meaning the dark grey-brown metal casting holding the corrector to the orange tube? There are Allen screws top and bottom. Remove them, and screw the counterweights into the holes? I've been studying the manuals and will hope to find a picture.


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Joe Cepleur
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Re: Fixing a C8 After Purchase new [Re: DAVIDG]
      #5060279 - 02/07/12 12:40 PM

Quote:

"Upon arriving home, the scope was tested with a known good 32mm Meade Series 4000 Plossl. I believe --I hope!-- it is badly miscollimated. Nothing comes to properly clear focus. the Moon looks fuzzy, as though its craters were covered with white mold. Stars are never pinpoints, but only faint, fuzzy dots."

Even in a bad collimated C-8, the image of a star will come to sharp focus, it won't be round, and will be coma shaped, but it will be sharp. The fuzzy dot appearance and fuzzy Moon sounds like a large amount of spherical aberration. The most likely cause is that the corrector has been flipped in the cell. The fact that the scope has a number of issues caused be the former owner and that the secondary cell is loose adds to the suspicion that corrector maybe backwards in it's cell.




Thanks! I had wondered whether the corrector might be in backwards, but only on intuition. How cool that the view matches what is actually to be expected. This also fits with one of the scope's oddities: The inside of the corrector is dirtier than the outside. Might guess the outside had been cleaned, except that the bigger dirt inside would have no better way to have gotten in there than to have been outside to start. The scope is so dirty that it clearly had lots of use, leading me to believe it will be good when we get it working. It may well have been cleaned somewhat, reassembled incorrectly, and then abandoned.

The manuals make a big deal of each corrector and secondary being hand-selected and perfectly aligned to 1/100th-wave. How am I going to put this back together correctly? The serial number on the corrector belongs in a specific location, but if a cat's whisker makes a difference, how will I align it? And what about the secondary? It's been flopping around for years. How do I determine which way to align it? Is there any easier means than star testing the scope between slight rotations of the corrector and secondary? How would I judge either's position if both the mirror and corrector had to be properly aligned for optimal result in a star test?

Is there any way to determine which side of the corrector faces out, other than to reassemble the scope and test it? Might the corrector's slight curvature result in any noticeable fun-house-mirror effect on the curved side? I believe only one side is curved, and it faces out?


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DAVIDG
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Re: Fixing a C8 After Purchase new [Re: Joe Cepleur]
      #5060392 - 02/07/12 01:40 PM

I've refigured a couple of Celestron optics sets and I'm getting ready to do another on my early C-8 which has the tri-color paint and is serial #316.
If the optics don't have residue astgimatism it doesn't matter how the corrector or the secondary is rotated. You won't be able to see the curve in the corrector since it is not that deep. Sometime you can see were the gasket have left a mark and tell the front from the back that way. Also sometime the serial number is etched into the edge of the corrector face and that is usually on the face that points out. If you have a small optical flat, you place it around the 70% zone (ie 70% from the center) of the corrector and you'll see that the interference fringes have a good amount of curvature so that is the side that has the Schmidt curve and that side faces the sky. In any case, you'll see a big difference between having it in the wrong way vs the right way. The right way cancels the spherical aberration of the primary, the wrong way doubles it.
You want to center the corrector in the cell and then center the secondary holder using the ID of the corrector cell as a reference. Position the secondary cell so one of the alignment screws is at the 12:00 o'clock position. This makes it easier to figure out what screw to turn. Look up the rear port in the scope and by eye center the secondary by using the alignment screws. Now center a fairly bright star, Polaris works well since it doesn't move out of the field very quickly, slightly defocus the star so your inside of focus and center the black circle which is the shadow of the secondary in the center of the defocused star. You want to be on the inside of focus because the movement of the alignment screws will match the way you want the secondary to move. If your on the outside of focus the secondary moves in the opposite direction.
The fact that you have more dirt on the inside of the corrector then outside is another strong clue that the corrector is flipped.

- Dave


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greju
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Re: Fixing a C8 After Purchase [Re: Joe Cepleur]
      #5060431 - 02/07/12 01:57 PM

Probably a little late but some good info.

http://www.scopereviews.com/C8History.html


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greju
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Re: Fixing a C8 After Purchase [Re: DAVIDG]
      #5060434 - 02/07/12 01:59 PM

"You want to center the corrector in the cell and then center the secondary holder using the ID of the corrector cell as a reference. Position the secondary cell so one of the alignment screws is at the 12:00 o'clock position."

I am not sure I have ever seen the alignment screws with one at the 12. Shouldn't they be in the same position as first assmbled or does that not matter?


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DAVIDG
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Re: Fixing a C8 After Purchase new [Re: greju]
      #5060478 - 02/07/12 02:23 PM

It doesn't make any difference were the alignment screws are positioned, it just makes it much easier to match up which way the secondary needs to be adjusted with the position of the screws.

- Dave


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Brian RisleyModerator
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Re: Fixing a C8 After Purchase [Re: greju]
      #5060514 - 02/07/12 02:48 PM

There are alignment marks to get things back in proper orientation. With the old scopes, it is easy if you have a laser collimator to get the secondary holder centered, it has a central hole for the secondary. Once you find the corrector serial # and the marks on the back of the secondary, we can get things aligned the way they were at the factory. The shims are probably not present or not in their correct positions beside the corrector. We can make new ones.
I have only seen one bad C-8 set of optics. It was so bad, the corrector didn't even properly fit the cell! (Serial #'s matched on all optics!) It had a bad burnthrough radial spike problem. Not sure if it was corrector or primary that was bad.

Brian


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Joe Cepleur
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Re: Fixing a C8 After Purchase [Re: Brian Risley]
      #5060516 - 02/07/12 02:52 PM

Good! Alignment marks will make this manageable.

What material would be used to make shims? I'd like to have it on hand when I disassemble the scope for cleaning.


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DAVIDG
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Re: Fixing a C8 After Purchase [Re: Joe Cepleur]
      #5060699 - 02/07/12 04:49 PM

You can use 1/8" cork or gasket material as shim stock. What is critical is that you center the corrector using the OD of it to that of the ID of the cell, then center the secondary cell to the ID of the corrector cell. The reason is that when they core the correctors the hole may not be perfectly centered. In the factory they would core a stack of correctors together and some would not perfectly aligned. I have seen a number that were off by 1/8" or more. My C-5 is this way. If you center the corrector by using it's OD, it will then be optically as well as mechanically centered.
If you first center the secondary in the corrector then center the secondary holder, and the hole is not perfectly centered, the corrector will be optically off center. What will happen is that scope will look perfectly aligned but you'll get on axis coma and all the stars in the field will show coma pointing in one direction. Many people think it's the secondary being misaligned and will pull their hair out trying to get things right.

- Dave


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Joe Cepleur
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Reged: 03/18/10

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Re: Fixing a C8 After Purchase [Re: DAVIDG]
      #5060870 - 02/07/12 06:23 PM

That story of off-centered holes in corrector plates is a revelation! Celestron advertised in its literature of the day that, although any combination of corrector, primary, and secondary would work well, they carefully selected, and aligned by hand, the best combinations for the finest possible results. I had not been able to understand how it would be possible to specially tweak spherical mirrors or radially uniform correctors. You're saying that, actually, the manufacturing process was sloppy at this stage, but they had a means to overcome its deficiencies?

Would it have been impossible to perfectly center all the holes? It may have made no difference during assembly at the factory, but think how much easier it might have been to reassemble the scopes after taking them apart for repair or cleaning.

A new question: Would there be any advantage to flocking the tube?


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Joe Cepleur
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Reged: 03/18/10

Loc: Dark North Woods
The Plot Thickens: Fixing a Salt-Encrusted C8 [Re: Joe Cepleur]
      #5061841 - 02/08/12 10:11 AM Attachment (36 downloads)

Some things are wonderful when encrusted with salt: fresh pretzels from Pennsylvania Dutch country, smoked fish from the coast of Maine. Telescopes? Maybe not so good. I like 'em clean. I figured that Brandon was worth forty or fifty dollars when I bought the scope, and am please to have been misinformed. What is the real value? $150? More? Makes me feel pretty good having spent $250 on a scope that won't focus, yet I believe this tale may yet have a happy ending.

The greatest thread ever on Cloudy Nights Classic Forum read like a detective novel. Beginning with a name and address in the United States written on the case of an oddly fine, costly telescope manufactured in Paris, and continuing through public records of court cases, the story traced the scope's provenance to organized crime rigging horse races in the 1930s. The bookies would accept bets until just after a race was over, and then play a recording of its radio broadcast to the bettors that was just slightly delayed from real time. Knowing which horse had already won the race told the bookies which late bets to accept or reject, because an accomplice on the telephone would have already reported the results as he had seen them through the telescope. The current thread will not be quite that cool, but I may yet get my fifteen minutes of fame.

The following fourteen photographs, I promise, contain all the additional evidence necessary to deduce all relevant facts about the actual history of this particular C8: how it came to be encrusted in salt, and whether there is hope for its repair. To make it easier, the smoking gun will be present in the very first image. (Remember, the seller states that the scope was used for many years by the sea.)

Ready to play, super-sleuths?

When I wakened this morning and went to the window to see the sun rise over the frozen lake, I happened to look into the C8's tube and saw that the light was streaming into so as to finally allow a good photograph of the inside. A moment later, I saw the smoking gun. Can you see it? Like a deep space object, it is hidden in plain sight:

Edited by Joe Cepleur (02/08/12 01:00 PM)


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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 [Re: Joe Cepleur]
      #5061842 - 02/08/12 10:12 AM Attachment (45 downloads)

With salt everywhere, there is an issue with the camera's depth of field. It is not possible for a close-up image to focus on both ends of the telescope at once, so this thread contains a series of not-quite duplicate images. The prior image focused on salt on the corrector. This one focuses on salt on the primary:

Edited by Joe Cepleur (02/08/12 12:53 PM)


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