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Can a Celestron C102-HD Refractor be collimated?

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#26 audioaficionado

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Posted 11 May 2013 - 03:45 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.

#27 csrlice12

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Posted 11 May 2013 - 09:12 PM

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

#28 audioaficionado

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Posted 12 May 2013 - 01:04 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.

#29 csrlice12

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Posted 12 May 2013 - 05:32 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..... :lol:

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

#30 BoriSpider

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Posted 13 May 2013 - 04:43 PM

+1 White Lithium
That's what I used.

#31 audioaficionado

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Posted 14 May 2013 - 02:21 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...

#32 csrlice12

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Posted 14 May 2013 - 07:38 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!

#33 Zamboni

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Posted 14 May 2013 - 09:46 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.

#34 audioaficionado

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Posted 14 May 2013 - 01:35 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.

#35 audioaficionado

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Posted 15 May 2013 - 02:31 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.

#36 csrlice12

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Posted 15 May 2013 - 09:21 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...

#37 audioaficionado

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Posted 15 May 2013 - 10:13 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.

#38 csrlice12

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Posted 15 May 2013 - 10:26 AM

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

#39 audioaficionado

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Posted 15 May 2013 - 10:38 AM

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

#40 audioaficionado

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Posted 17 May 2013 - 06:13 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.

#41 csrlice12

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Posted 17 May 2013 - 08:02 AM

That scope came with a cheap, but fairly accurate, GoTo mount for $199 at Costco during Christmas season. The scope itself in pretty much the same as the 102HD and have been pretty highly praised for the price. $160 seems a little high.

#42 audioaficionado

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Posted 17 May 2013 - 10:05 AM

It comes with a 2" mirror diagonal. Otherwise it costs $120.

I just don't have the bux for the good scopes right now.

Later this summer maybe I can get a good setup, but for now I'm scopeless save for this low cost OTA.

Craig's list hasn't had anything decent for months now. Mostly kids junk toys or over priced antiques.

#43 Zamboni

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Posted 17 May 2013 - 11:43 AM

I'd say get the GT OTA from OPT and pop off the existing dovetail rail. The tube rings you have will work, since the only difference is the lens cell/dew shield. Re-lube the CG4 mount with the lithium grease and fill the tripod legs with Bondo to stiffen them. After that you'll have a very useable scope with quite nice optics. Ed Ting did a review of the OTA from OPT and gave it high marks.

http://scopereviews.com/page1af.html

#44 Martin

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Posted 17 May 2013 - 11:55 AM

Hi,
Not sure if this was already brought up or not. Can't you just elongate the existing holes in the tube or in the cell with a dremel tool or something and then get the cell to align better with the tube, you will have more adjustment room then.

Martin

#45 audioaficionado

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Posted 17 May 2013 - 03:26 PM

http://scopereviews.com/page1c.html#10

Hmmm...

Looks like my mounting rings will be too large for a simple plug and play approach.

The tube is no longer 114 mm in diameter, it's now 102 mm, which means the OTA isn't baffled as well as before (there are 3 on mine.)



Mine definitely has some good baffles.

#46 Zamboni

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Posted 17 May 2013 - 05:20 PM

The 114mm tube only applies to the old Vixen C102 with the Great Polaris mount. The C102HD has the 102mm tube which is identical in diameter to the 102gt.

#47 audioaficionado

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Posted 17 May 2013 - 06:57 PM

Yep I just threw a tape measure across the C102HD rings and they're 102mm so I'm good to go.

#48 audioaficionado

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Posted 21 May 2013 - 01:53 PM

Well the new OTA should arrive this Thursday and the skies should be clear by Friday.

I'm not going to toss the broken OTA, but it's a lot easier to work on if it's not your only scope. No pressure to get it working asap.

If I still get stumped, I will have a shipping box to send it out for a second opinion from a more experienced astro guy.

#49 audioaficionado

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Posted 24 May 2013 - 07:41 PM

Got the new C102-GT OTA yesterday and the Agena collimating eyepiece shows it to be true. Of course I've got a solid cloud deck overhead. :noway:

I'll keep peeking outside tonight for any cloud breaks long enough to do some star tests and look at a planet or two.

Most of next week will be cloudy too :cloudy:

#50 Zamboni

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Posted 25 May 2013 - 01:47 PM

Pics or it didn't happen!






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