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Equipment Discussions >> Cats & Casses

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Rich Wagner
journeyman


Reged: 07/07/11

Super C8 OTA Slips out of position new
      #4927541 - 11/21/11 10:18 AM

I picked up a Super C8 with a Byers worm gear drive this weekend. The scope is in decent shape but was missing the power cord and the 3 bolts to secure the wedge. I found the cord on scopestuff now i am searching for the wedge bolts.

The real problem is that the tube slips out of its rear, im not sure what its called, round fixture when its horizontal. I noticed this when I was trying to collimate it. If i point to zenith the tube slides slides back flush against the back/ bottom.

When i move it horizointal you can see the tube slip about 1/2" so in essence the tube angles down 2 or 3 degrees more than it should be.

What should I check? Do I need to take the whole tube assembly apart? I cant tighten the screwa around the tube any more than i already have done without stripping them.

This is my first SCT and I really am flying in the dark here. Any help would be great!

Regard,

Rich


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archer1960
sage


Reged: 07/26/11

Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #4927592 - 11/21/11 10:52 AM

Are you referring to the rings that go around the tube and attach it to the mount? And they're too loose? If that's the case, I'd suggest getting something to fill in the space, such as a strip of rubber or felt.

If that's not the issue, then try to explain in more detail or take a picture and show us what you're referring to.


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Rich Wagner
journeyman


Reged: 07/07/11

Re: Super C8 OTA Slips out of position new [Re: archer1960]
      #4927629 - 11/21/11 11:11 AM

Archer, I'm referring to the backend of the scope that holds the focuser and eyepiece tube. the tube slips into the round backend. There are screws around this part that appear to go into the tube itself to secure it. Basically the opposite end of the corrector plate.

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Rick Huber
sage
*****

Reged: 01/03/04

Loc: South of Cincy Ohio
Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #4927664 - 11/21/11 11:33 AM

Rich:
Can you take a pic? - There should be screws that go through the rear cell and hold the tube in place - Look down the tube (from the corrector end) and see if these screws are visible with nuts on them - My feeling is these are missing - If so then the OTA along with the corrector plate may be out of alignment - Anyway let us know and hope this helps some

Rick H
Same skies, older eyes


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Rich Wagner
journeyman


Reged: 07/07/11

Re: Super C8 OTA Slips out of position new [Re: Rick Huber]
      #4927697 - 11/21/11 11:59 AM

Here are some pics i took the other night. When the scope is placed horizontal it will slip out from under the top of the rear cell by the finder scope. i tightened everything. I even removed the finderscope and replaced the screws in that but the tube still slips.








Edited by Rich Wagner (11/21/11 12:01 PM)


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Rich Wagner
journeyman


Reged: 07/07/11

Re: Super C8 OTA Slips out of position new [Re: Rick Huber]
      #4927742 - 11/21/11 12:30 PM

Quote:

Look down the tube (from the corrector end) and see if these screws are visible with nuts on them - My feeling is these are missing




Rick I can see the screws but i don't see nuts on any of them. just standard allen head type screws


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archer1960
sage


Reged: 07/26/11

Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #4927915 - 11/21/11 01:58 PM

I still don't understand what it is that's slipping, and where it's coming from. Can you shoot a couple of pics that show "it" both fully seated and then slipped out?

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rmollise
Postmaster
*****

Reged: 07/06/07

Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #4927949 - 11/21/11 02:19 PM

Quote:

Here are some pics i took the other night. When the scope is placed horizontal it will slip out from under the top of the rear cell by the finder scope. i tightened everything. I even removed the finderscope and replaced the screws in that but the tube still slips.





It's very unclear what is slipping. Is the rear cell threatening to come off the scope? Is the finder falling off? Is the visual back loose? Is the scope slipping in declination?


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Rich Wagner
journeyman


Reged: 07/07/11

Re: Super C8 OTA Slips out of position new [Re: rmollise]
      #4928056 - 11/21/11 03:16 PM

I'll snap some pics when i get home but ill try again, please excuse my newbness.

When the scope tube is level, horizontal with the floor on the fork, the top of the tube begins to slip out of the rear cell.

If i push up on the side of front of the tube, correct plate part, the tube slips back flush into the rear cell. If i release my hand from the tube it slips back out of the rear cell. Not all the way but at least 1/2 inch. It's like there should be a screw there preventing this from happening but all the screws around the rear cell are tight, none missing.

I hope that helps a little...


Thanks!


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greedyshark
professor emeritus
*****

Reged: 10/31/05

Loc: 3rd Rock
Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #4928109 - 11/21/11 03:51 PM

Are you saying that the glossy black tube is not secured to the heavy dull black rear unit?

Charles


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Rick Huber
sage
*****

Reged: 01/03/04

Loc: South of Cincy Ohio
Re: Super C8 OTA Slips out of position new [Re: greedyshark]
      #4928680 - 11/21/11 10:08 PM

Rich:

Still a bit unclear on what is slipping - FYI the finderscope mounting has nothing to do with holding the OTA - There should be screws on the perimeter of the rear cell - Can you take some side pictures (left and right) - Also, try to take the side pictures with the tube in its most forward and rear movement -

That should help clarify what you are describing

Rick H
Same skies, older eyes


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Wmacky
Carpal Tunnel
*****

Reged: 11/24/07

Loc: Florida
Re: Super C8 OTA Slips out of position new [Re: Rick Huber]
      #4928686 - 11/21/11 10:15 PM

Could the nuts have come loose from the perimeter screws?

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Twilight
scholastic sledgehammer


Reged: 06/03/10

Loc: Englewood Tennessee
Re: Super C8 OTA Slips out of position new [Re: Wmacky]
      #4928927 - 11/22/11 02:20 AM

Rich,
If I am understanding you correctly is it possible that the screw holes on the OTA/Tube have become elongated and is allowing the OTA/Tube to slip out of the rear cell. Are you sure the screws around the circumference of of the Cell are tight and the nuts inside are not turning and are tight?

It really sounds to me like the holes in the OTA have become elongated. Is the tube only slipping out from the top of the cell or is it slipping out all the way around the edge of the cell?


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Rich Wagner
journeyman


Reged: 07/07/11

Re: Super C8 OTA Slips out of position new [Re: Twilight]
      #4929082 - 11/22/11 07:53 AM

I haven't taken the corrector lens off to look inside yet. This is my first sct so i had no idea there were even nuts inside the tube. But i did make a video demonstrating the movement of the ota. Hopefully this will help.

http://www.youtube.com/watch?v=MDVvzgRPxUE


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Rick Huber
sage
*****

Reged: 01/03/04

Loc: South of Cincy Ohio
Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #4929107 - 11/22/11 08:16 AM

Rich:
Okay watched the video - No doubt the perimeter screws are not holding the OTA in place - The movement does not appear to be 1/2" but quite a bit less which again indicates the screws are the problem.

As far as removing the corrector plate - You will have to do this to fix this problem, but, before tackling that be sure to read up on exactly how to do it - there is plenty of info available on the correct procedure - Once you have removed the corrector be careful about the main mirror - In order to get the nuts back on the ota perimeter screws you may have to remove the main mirror -

Keep us up-to-date on your progress and BE CAREFUL!

Rick H

Same skies, older eyes


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Rich Wagner
journeyman


Reged: 07/07/11

Re: Super C8 OTA Slips out of position new [Re: Rick Huber]
      #4929252 - 11/22/11 10:00 AM

Thanks for everything folks! I'm going to take it apart, bolt and nut everything down, flock the tube and clean the corrector plate. Hopefully I'll be able to document my process as I go through it good enough to post here.

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Twilight
scholastic sledgehammer


Reged: 06/03/10

Loc: Englewood Tennessee
Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #4930586 - 11/23/11 01:40 AM

Rich, From looking at you video I am pretty sure you are going to find the holes at the top have become elongated some what. Most likely just the ones on top. If the scope has been used a lot with the screws loose it could wear the holes in the thin metal very easy over time. Good luck with the repair and maintenance.

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silversurfer
super member


Reged: 05/31/04

Loc: Austin, TX
Re: Super C8 OTA Slips out of position new [Re: Rich Wagner]
      #5717441 - 03/06/13 10:38 PM

Hey Rich,
Were you ever able to fix this? If so, could you give some details? I have the same problem with a C8 I just acquired.
Thanks!


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Super C8 OTA Slips out of position new [Re: silversurfer]
      #5717885 - 03/07/13 08:14 AM

Make sure and mark the glass corrector plate and front cell on the edge before you take it out, it has to go back the same rotational aspect.
You will also have to pull the Primary mirror out to get to the screws on the rear cell.


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Eddgie
Postmaster
*****

Reged: 02/01/06

Re: Super C8 OTA Slips out of position [Re: silversurfer]
      #5717961 - 03/07/13 09:16 AM

There is another critical point.

The holes for the tube are not precision drilled for tube alignment to the optical axis.

This means that if you don't take special precautions, the tube can be tilted with respect to the optical axis.

This is a very bad condition to have.

When you re-assemble, you can try measuring from the front edge of the rear cell to the rear edge of the front cell at several positions to ensure that the distance is as exact as you can possibly get it.

While you still may not get it perfect perfect, you have to get it close enough so that if you have to re-center the corrector, there is enough side-to side movement to accomplish this.

Taking the tube loose is necessary in this case, but getting it back into perfect alignment can be a bit of a fussy proposition.

And again, it doesn't have to be perfect perfect, but close enough so that if the corrector needs to be moved a bit to get your centering back, there will be room enough for it to move laterally.


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