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Equipment Discussions >> Refractors

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: Zamboni]
      #5851878 - 05/10/13 11:55 AM

Glass is a super cooled fluid. I hope the dozen years it was stashed in the previous owner's garage wasn't enough time to permanently warp the lens elements while they were under stress.

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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5851916 - 05/10/13 12:22 PM

I imagine after you clean it all up, and get the front lens configuration set right, and tune up the focuser, it'll work fine. Those C102HDs are actually a pretty decent scope. Be sure to look to see someone didn't put the spacers back on the wrong side of the lens too..seems the front lens assembly is where your problem lies.

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Eddgie
Postmaster
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Reged: 02/01/06

Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5853046 - 05/10/13 11:55 PM Attachment (30 downloads)

Attached is a picture that shows three conditions.

The top is coma. When you say "triangular" some could see that the in focus star has a somewhat triangular shape.


The second image is astigmatism. notice that in focus, the star looks like a cross, and out of focus, the pattern is stretched in different directions on either side of focus.

The last image is triangular and is "Pinch" caused by having the retaining ring to tight.

Which of these most resembles what you see?


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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: Eddgie]
      #5853131 - 05/11/13 01:01 AM

Coma looks much closer than the pinched one. Astigmatism doesn't look at all like what I'm seeing.

I suppose it's possible to have a combination too.

Too busy today working on my front brakes, but I'll get into the guts of this scope soon and see what I can find out.


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buddyjesus
Carpal Tunnel
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Reged: 07/07/10

Loc: Davison, Michigan
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: Zamboni]
      #5853179 - 05/11/13 02:15 AM

might still be a bit too tight. I hear a tiny click when moving between horizontal and vertical just to give you an idea.

what eyepieces are you using to test? Plossl eyepieces give me about a 20% area around the margin that has aberrations.


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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? [Re: buddyjesus]
      #5853253 - 05/11/13 04:45 AM

EPs are all in my sig. The ring is looser than before and I can still hear a slight knock if I tap it harder.

I'll try and pull it apart today if I have time. I'm working nights on the weekends so I won't be able to check out the view until Monday.


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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5854474 - 05/11/13 10:12 PM

Actually looking forward to see what this turned out to be.

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: csrlice12]
      #5855565 - 05/12/13 02:04 PM

While I'm at it, what is a good low vapor pressure grease for my focuser that doesn't spread all over like cancer? Lowes or Home Depot would be nice so I don't have to mail order and wait for yet another item for this project.

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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5856064 - 05/12/13 06:32 PM

White Lithium, I just got a tube a few minutes ago by chance at Lowes for under $4. On the focuser tube itself, it actually takes very, very little. actually just rub a tiny, tiny dab between your finger and thumb and then rub your finger on the plastic/teflon guides in the focuser, that should be enough for the tube itself. The gears for a rack&pinion focuser will take a small dab. One tube should last generations....I belive the stuff Celestron currently uses was Lithium grease left over from Galileo's first scope mod.....

This is also the grease you can replace the Synta glue in the mount gears....

Edited by csrlice12 (05/12/13 06:40 PM)


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BoriSpider
Carpal Tunnel


Reged: 08/10/04

Loc: S.W.FLA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: csrlice12]
      #5858095 - 05/13/13 05:43 PM

+1 White Lithium
That's what I used.


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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: BoriSpider]
      #5859119 - 05/14/13 03:21 AM

Picked up the Li grease.

Took out the lenses from the lens cell. They didn't appear to have been taken apart. They had 3 metallic looking spacers that had some double stick tape adhesive on both sides. I gently pried them apart, which I think was a mistake, but I had to see if a backwards element was the issue. I'd marked the edges so they could be realigned again. I cleaned them and put them back into the plastic lens cell.

There's some serious miscollimation in the whole scope. My collimation tool shows very bad issues with the draw tube focuser and diagonal.

I took the diagonal out and just used the focuser and the EPs to look at Saturn and Spica again. The view still sucks with bad distortion as I've previously described.

I'll try and tighten up the slop in the focuser and the collimation angles at it's attachment point on the tube with the 3 screws.

I'm not giving up yet, but I sure wish I had a nicer scope that just worked without all the drama.

GoTo with tracking sounds wonderful too. The CG-4 GEM has more slop than a hog trough.

To be continued...


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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5859340 - 05/14/13 08:38 AM

Think of it as a summer project...have it ready for Jupiter's reappearance.....

The OTA's not warped or anything is it??? Probably is the focuser. S&S Optika in Denver has a used focuser from an Celestron 102XLT (pretty much same scope as the C-102HD) for like $30 (somebody swapped it out) that should fit. Maybe give them a call (websearch "S&S Optika", they'll pop up in your browser. This is a small scope shop in Denver, they don't do internet sales, but will deal over the phone...) Good Luck!


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Zamboni
scholastic sledgehammer
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Reged: 01/03/05

Loc: Colorado Springs
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: csrlice12]
      #5859564 - 05/14/13 10:46 AM

It's also worth mentioning that in the earlier production runs of the C102HD there was some pretty uneven quality control and quite a few lemons slipped through the cracks. Depending on when it was made, it could just be a bad lens.

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: Zamboni]
      #5860086 - 05/14/13 02:35 PM

If it was the lens, coma should have rotated since it would be almost impossible to randomly get the lens unit back in the cell with the original orientation. The coma orientation looks the same as the focuser miscollimation orientation. The local stargazing weather is deteriorating for awhile. Maybe this is a good sign I'll get it fixed today LOL.

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5861444 - 05/15/13 03:31 AM

Progress:

It's looking like the lens cell itself is badly out of alignment relative to the OTA body. It mounts with 3 countersunk screws so the dew shield can slide over and onto the cell against a stop flange. There isn't any easy way to fix this as it's not adjustable. I tried rotating the cell one hole at a time and none of those positions fixed the miscollimation issues. One of the screw holes in the steel OTA tube is somewhat stripped and another is not perpendicular to the body surface. Looks like either the previous owner screwed it all up putting it back together or it was one of the lemons produced by sloppy worksmanship at the Synta telescope factory back in 1999.

I'm not sure how to fix this so it's robust enough to stay collimated even when the dew shield gets taken on and off and gets the occasional bump going through doorways etc.


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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5861810 - 05/15/13 10:21 AM

rotate the lens cell and drill new holes is your only choice, or replace the OTA tube, but at this point, It'd be cheaper to buy a new scope if rotating the lens cell doesnt work (you may have to rotate the focuser too, depending on how it collimates). Good luck with this one...

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: csrlice12]
      #5861901 - 05/15/13 11:13 AM

I was thinking of getting it adjusted w/o the screws and using little dabs of blue Locktite 242 to temporarily hold it in place. If that fixes the optical problem, I can just use real glue to set it.

I can't in good conscious re-Craig's list this thing unless I can get it fixed. So it's a good thing I'm only into it for the $150 I originally paid. The subsequent eye pieces I've invested in were needed in any event for any and all other scopes I'll get in the future.

Note to self:

If you can't star test a used scope before you buy it, you have to roll the dice.


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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5861924 - 05/15/13 11:26 AM

As a last resort, use it as a club against unwanted varments....

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: csrlice12]
      #5861956 - 05/15/13 11:38 AM

I could use the lens cell to start my campfire while standing LOL.

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audioaficionado
professor emeritus


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Can a Celestron C102-HD Refractor be collimated? new [Re: audioaficionado]
      #5866517 - 05/17/13 07:13 AM

Celestron 102mm NexStar GT OTA with 2" Diagonal for $160

Looks to be a good replacement OTA. I don't know if the mounting rings I have will fit.


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