18 replies to this topic

[DAVIDG]

 Back in the Fall my club was donated a couple of telescope from a near by college. One was old C8 with the rare coxial focuser  and the rare table top feet. It is serial number 82.  What is weird about it  is that some parts are more modern then the rest. The tube does not have the tri-color orange paint but the next generation pebble finished orange. Also the drive base is old with the Cinch Jones two prong plug, but  it is next generation up from  the original base that used a different clutch assembly with the lock for the clutch off to the side vs directly behind the slow motion control.  The forks , finder and mirror cell are the original with tri-color paint.

     Here is a  picture of it when I brought it home yesterday.

 

                  - Dave 

     

[DAVIDG]

 Here are pictures of the forks and mirror cell showing the original tri-color paint  and  tube that has the more modern pebble finish orange. Also the finder with the tri-color paint 

 

                - Dave 

 

 

[DAVIDG]

 Here is  a picture of the rare table top legs  and the drive base and a  picture of  the serial number on the coax focuser.

 

    - Dave 

 

 

[apfever]

Central tube swap the best I can tell because the finish distinctly does not match the rest of the scope for condition alone not to mention style. Does the front cell match the back and arms?

Somebody replacing just the center section of the tube would be capable of swapping anything else such as the base. Check the motors for dates, they should be dated around the rim. Sometimes you can find the dates with a mechanics (dentist) mirror while the motors are installed.  Motor dates are your biggest best option for the base. 

 

EDIT: We are cross typing entries. That base looks like a swap too, bet it has newer motors.

Edited by apfever, 02 January 2025 - 11:20 AM.

[DAVIDG]

 With the tube clearly being replaced I thought maybe it had been damaged and possibly the corrector has well and it might have been replaced.  The secondary cell is the correct vintage. So I removed the retainer ring for the corrector and found the serial number on the corrector. It is also #82 which matches the one on the focuser. Celestron would mark the mirror, secondary and corrector with the same serial number and hand figure the secondary to make a matched optical set.  With the corrector having the same serial number as the focuser and the secondary cell being the correct vintage that was strong evidence that the corrector and secondary were original. 

  My guess is the paint failed on the tube and when it did it would first get sticky so it was sent back to the Celestron  and they replaced the tube. Also the original drive bases had an issue with the clutch design so it was replaced as well.

   Here is a picture of the serial number on the corrector.

 

                 - Dave 

 

[jragsdale]

Is the serial the same on the drive base? And motor dates? Mine is Serial #66 so very similar to yours in a lot of ways, here's the video I made showing all the features of mine: https://youtu.be/IDfcWGFEQJQ

[DAVIDG]

 The corrector is not coated  and had  the typical amount of dirt and a film of haze for being that old ( 1972 ? )  Also the there were only two cork shims and the corrector was off center being pushed up against the cell on one side were there was no cork spacer . So the next step  was to remove the corrector and give it a bath. The problem was it was stuck and stuck good ! I drippled some alcohol around the edge and let it soak in for a few minutes. I then took a thin piece of Teflon that fit into the space on one the side and slowly worked it around the corrector while putting  light sideways press on it. After a bit it popped free.  The secondary was in perfect condition. I placed a plastic bag around the secondary and into the sink for nice warm bath.  It cleaned up perfectly !  So back into the scope it went. I used three new shims made of Teflon to hold it centered in the cell.  I also placed the serial number at the 3 o'clock position like the factory would even thou it makes no difference and orientated the secondary cell  so one of the adjustment screws is at 12:00 o'clock. This make collimating the optics much easier. 

   Here is  a picture of the clean corrector and it back in it's cell. The stars are were the Teflon spacers are  and the circle is around the serial number 

 

                - Dave 

 

 

 

 

 

 

[DAVIDG]

 The next step  was to set on the table on my deck and collimate the optics. It was cold and winding but  a clear night. With the secondary cell having the screws orientated with one at 12:00 o'clock it was easy to get collimated. I then let it cool down. Jupiter was almost  straight over head and  the image was excellent show a wealth of details. A few weeks earlier I had tested the scope with my double pass setup and it show very good correction for spherical with some typical roughness and small turned edge. I need to retest since the edge might have been from the retainer ring being screwed down too tight. The screws need to be just lightly and evenly  tightened down not wrench down with 100 lbs. of torque like a typically find them. 

   The next step is to  look at the drive base and make a cord for it. I have cords from other old Celestrons that I used to test this one and the motors run. There is some play in the mount I need to address. Over all I'm pleased with this one since I also wanted a coax focus model.

 

                   - Dave 

[tim53]

 With the tube clearly being replaced I thought maybe it had been damaged and possibly the corrector has well and it might have been replaced.  The secondary cell is the correct vintage. So I removed the retainer ring for the corrector and found the serial number on the corrector. It is also #82 which matches the one on the focuser. Celestron would mark the mirror, secondary and corrector with the same serial number and hand figure the secondary to make a matched optical set.  With the corrector having the same serial number as the focuser and the secondary cell being the correct vintage that was strong evidence that the corrector and secondary were original. 

  My guess is the paint failed on the tube and when it did it would first get sticky so it was sent back to the Celestron  and they replaced the tube. Also the original drive bases had an issue with the clutch design so it was replaced as well.

   Here is a picture of the serial number on the corrector.

 

                 - Dave 

 

corrector plate serial number.jpg

this makes the most sense to me.  I've also wondered if any tricolor C-14s are out there, or if they were "all" repainted due to the paint failing and the fact that they were pretty expensive for the buyer.  Celestron might have been okay with repainting a handful of C-14s, but reluctant to repaint hundreds or thousands of C-8s.

[deSitter]

 The corrector is not coated  and had  the typical amount of dirt and a film of haze for being that old ( 1972 ? )  Also the there were only two cork shims and the corrector was off center being pushed up against the cell on one side were there was no cork spacer . So the next step  was to remove the corrector and give it a bath. The problem was it was stuck and stuck good ! I drippled some alcohol around the edge and let it soak in for a few minutes. I then took a thin piece of Teflon that fit into the space on one the side and slowly worked it around the corrector while putting  light sideways press on it. After a bit it popped free.  The secondary was in perfect condition. I placed a plastic bag around the secondary and into the sink for nice warm bath.  It cleaned up perfectly !  So back into the scope it went. I used three new shims made of Teflon to hold it centered in the cell.  I also placed the serial number at the 3 o'clock position like the factory would even thou it makes no difference and orientated the secondary cell  so one of the adjustment screws is at 12:00 o'clock. This make collimating the optics much easier. 

   Here is  a picture of the clean corrector and it back in it's cell. The stars are were the Teflon spacers are  and the circle is around the serial number 

 

                - Dave 

 

cleaned coorector.jpg

 

correct plate installed.jpg

What is the haze and it comes off with soap alone?

 

-drl

[DAVIDG]

What is the haze and it comes off with soap alone?

 

-drl

 I don't know what the haze was but it with the  typical dirt from being 50 year old glass came right off  with dish soap and  a warm bath. The corrector is pristine now.

  I made a power cord for it and  next going to see were the play is, in the drive.

 

                  - Dave 

 

[ccwemyss]

I'm curious about how you went about centering the corrector. It's been a long time since I've had it apart, but I seem to recall that the corrector on my C14 wasn't perfectly even around the exterior. Do you have a method to center it optically? And what about centering the tube on the optical axis?

 

Chip W. 

[DAVIDG]

 The drive was an easy fix, just had to adjust the motors so they messed better with the main gear and now no more play. The dates on the motor show  11-75. So some time in that time frame it must have went to back to Celestron for repair.

   It  is clear but cold here so I'm taking it  out so it can  cool down and I can get a look at Venus and Saturn right after sunset.

 

                         - Dave 

[DAVIDG]

I'm curious about how you went about centering the corrector. It's been a long time since I've had it apart, but I seem to recall that the corrector on my C14 wasn't perfectly even around the exterior. Do you have a method to center it optically? And what about centering the tube on the optical axis?

 

Chip W. 

 Chip this one was beautifully round  so it was just a matter of getting the gap uniform all the way around. I then used Teflon shims that just fit in the gap toi keep it centered. As I said the screws on the retainer then need to be evenly tighten lightly and not cranked down like I typically find them.

   In the past I have just tried to get the majority of the gap uniform for non round correctors. The corrector  is a bit forgiving optically, what is not is the secondary since no matter what  any one say it has aspheric figure which means it has an optical center. So it needs to be optically centered. What I do is make sure the secondary is centered on the mounting plate.  Then I use the center bolt  in the secondary cell as a  reference and inner edge of the corrector cell as the other reference surface  then center the secondary cell in  corrector cell.  So if the primary is optically centered to the mechanical axis of the scope,  the secondary will now be optically centered as well. 

   You also need to be sure the primary is centered and  also not tilted.  I use string across the corrector cell to form an X and a laser in the focuser should hit the dead center were the strings cross. The reflection of the strings in the mirror should also be dead center or the primary is tilted.  See this thread that more clearly explains the String method of checking the primary. https://www.cloudyni...-c8-to-another/

 

                     - Dave 

[deSitter]

I'm curious about how you went about centering the corrector. It's been a long time since I've had it apart, but I seem to recall that the corrector on my C14 wasn't perfectly even around the exterior. Do you have a method to center it optically? And what about centering the tube on the optical axis?

 

Chip W. 

I think David once mentioned that the center bore might be eccentric, and you had to make sure to check for this in advance and compensate with the positioning of the secondary cell. The figure on the corrector I imagine is guaranteed to be centered because of the way it is made. But I had assumed they bored the center hole first, so wouldn't feed an eccentric one into the corrector mill. Maybe I am imagining that.

 

-drl

[DAVIDG]

I think David once mentioned that the center bore might be eccentric, and you had to make sure to check for this in advance and compensate with the positioning of the secondary cell. The figure on the corrector I imagine is guaranteed to be centered because of the way it is made. But I had assumed they bored the center hole first, so wouldn't feed an eccentric one into the corrector mill. Maybe I am imagining that.

 

-drl

  The corrector is made with no hole and bored after it is made. Yes I have found a number of correctors were the center hole is not centered. It is my understand that Celestron would stack a couple of correctors on top of each and then bore them at once and that caused the  holes sometimes being off center.  This was done by hand on a drill press so nothing fancy. This is why I don't rely on centering the secondary cell  in the hole in the corrector.  If the secondary is centered on it's mounting plate which I check and center it if need be then the center bolt on the cell is also a reference for the center of the secondary. As I said I use that and the inner surface of the corrector cell to measure between it to get the secondary centered. 

  I have used my method for years and it has turned some pretty poor performing scopes into acceptable ones or better.  You never know what has been done to these old scope so I take nothing for granted and check everything. 

 

                     - Dave 

Edited by DAVIDG, 03 January 2025 - 10:06 AM.

[CHASLX200]

Could be a mix match.

[NinePlanets]

I'm reminded of an old Johnny Cash song...

 

https://youtu.be/Hb9F2DT8iEQ

[DAVIDG]

 I have been having fun using  my old C-8. I have noticed on  Jupiter and Mars I was getting some glare around them. I took a look up the focuser in the daytime and the inside of the baffle tube was letting in some  stray light.  I rolled up a piece of black velvet flocking paper into a  tube and used double sided tape on the back to hold  the flock  tube in place   The flocking reduced the stray light by a good amount.

 

                                   - Dave 

 

 

Edited by DAVIDG, 12 January 2025 - 08:21 PM.