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Original orange tube Comet Catcher

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#1 droid

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Posted 01 January 2013 - 06:18 PM

Ok I have a few posts from some here who took old Celestrons apart in the past.
And I need help.
I own this Comet Catcher, but have not ever been able to collimate it.
And its way off, I took the mirror cwll assembly apart, ok removed it from the tube, took all three mirro clips loose, swiveled them down and this mirror aint budging.Why the clips, lol.
It appears to have a cork pad under the mirror , and I cant tell if if its been glued in , or just gummed up so bad it might as well be glued in.
The problem is , supposedly, you loosen the large central screw on the bottem, then collimate by moving the three screws, but the large screw is frozen as well, and the three small collimation screws are moving.
Help!!!!!

#2 DAVIDG

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Posted 01 January 2013 - 07:15 PM

The mirror cell design is a center "puller" bolt and three outer "pusher" bolts. Since you have the cell out of the tube, you should be able to back the three outer screw all the way out allowing the plate hold the mirror to rotate. I think what has happened is that on the back surface of the plate that holds the mirror, there are three raised areas that the collimation bolts push against and plate has rotated so the screws are no longer touching these areas. The screws aren't long enough to touch the back of the plate unless they are under these raised areas.
Also be careful about tighten the center pivot bolt since it might be threaded into thru hole in the mirror mounting plate and if you tighting it to much, or the bolt will be pressing on the back of the mirror.

- Dave

#3 droid

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Posted 02 January 2013 - 06:06 AM

David; Ill give that a try, ty for responding.

#4 orion61

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Posted 02 January 2013 - 03:27 PM

The secondary is adjustable as well,
Best to use a laser collimater and check it first, pull the Primary then I make a Cross from string and center the laser dot on it.
You should be able to use a Cheshire eyepiece otr an empty
35mm film canister with a small hole drilled in the middle
as you loosen one of the 3 rear screws you tighten another
to align it, don't worry about the center one.
I hope yours has less Spherical Aberration than Mine,
might well not even have a corrector plate, yukk.

#5 GlennLeDrew

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Posted 02 January 2013 - 05:48 PM

I did a double-pass autocollimation Ronchi test on my old orange Comet Catcher. I was astonished at how smooth and well corrected it is! It's a keeper, and one day I may even give the corrector a good coating...

#6 droid

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Posted 02 January 2013 - 06:29 PM

Actually mine has never had pin point images, but at this focal length I never expected it to.
The scope as collimated currently, according to the Orion Lazer collimator , is dead on, yet , the main mirror image only takes up roughly 80percent or so , maybe a shade less , of the secondary, and towards the top so there is empty secondary going to waste, it almost appears the secondary is to large for the scope.
I dunno, leave well enough alone maybe, I will attempt to take some photos tomorrow.

#7 droid

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Posted 03 January 2013 - 01:36 AM

heres a fairly good image of what my secondary looks like in relation to the eye peice tube and main mirror, yes the miror is dirty, lol

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#8 GlennLeDrew

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Posted 03 January 2013 - 02:35 AM

Andy,
It would seem that your secondary might not be displaced sufficiently far rearward and/or away from the focuser. Given the apparent offset away from the focuser as shown in your photo, it seems the larger component of offset remaining involves moving the secondary longitudinally, closer to the primary mirror.

#9 orion61

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Posted 03 January 2013 - 08:18 AM

Those secondarys are part of the focuser, and not adjustable, The whole secondary slides along a track
to achieve focus.

#10 DAVIDG

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Posted 03 January 2013 - 09:34 AM

My Comet Catcher also gives excellent images and I also tested via double pass autocollimation like Glenn which also showed the optics to be excellent. If one is giving a bad image, and the collimation is good I would check that the corrector plate is installed correctly. I have seen a number Schmidts were a former owner dissassmbled the telescope and flipped the corrector be mistake. This sometime lead people to believe that the corrector has been replaced by window glass.

- Dave

#11 GlennLeDrew

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Posted 03 January 2013 - 12:17 PM

Orion61,
Yes, the secondary is carried along on a sled focuser. Nonetheless, its relative position with respect to the focuser tube is adjustable, via the three 'pusher' screws, just like any Newtonian.If it were not, the instrument might well be unusable.

Dave,
Reversing the corrector should result in practically no discernible difference in correction. It's basically a net zero power element, of quite low optical power. The induced spherical aberration, whether oriented 'correctly' or not, is to all intents and purposes identical.

#12 orion61

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Posted 03 January 2013 - 01:50 PM

Yes Glen your right I posted that up a couple I mis read your post sorry..
Those scopes are an enigma to me, I have had 3 of them and thought them rather shoddy optically,
With the abilitys of todays Digital technology and short
exposure time (compaired to my old self Hypered Tech Pan and Fuji 400 film) of 60 plus minutes, guiding for 10-15 minutes is a breeze!
My results always had very bloated Stellar images with my Comet Catchers, they also had so much SA it bothered me to no end,being unable to get a crisp focus.
Heck might as well heft up an Astroscan...LOL but if there are good ones optically I could see the merit. I just havent looked through one.

#13 DAVIDG

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Posted 03 January 2013 - 03:10 PM

Glenn,
When you flip the corrector the angle of the rays is reserved so any divergent rays become convergent. This adds spherical aberration instead of reducing it. There are also a family of Schmidt curves, some have less of problem then other when flipped depending on there exact shape and were they are placed in relationship to the primary. You also have the issue that the back surface is rearly flat but usually a few waves concave or convex which also had aberration. If the primary is slightly aspherized to remove is, it will effect the overall correction if the corrector is flipped around.
Here is a spot diagram of Schmidt camera were the corrector is flipped The on axis correction is still pretty good but the off axis correction has become worse.

- Dave

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#14 DAVIDG

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Posted 03 January 2013 - 03:12 PM

Here is that same Schmidt system with the Schmidt curve on the correct side of the plate.

- Dave

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#15 GlennLeDrew

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Posted 04 January 2013 - 03:04 AM

David,
Your example is of a *very* fast f/1.25 camera. The Schmidt corrector's curves are hence quite strong and therefore more sensitive to orientation. Particularly so the greater the difference in shape on each surface of the corrector.

At the Comet Catcher's f/3.64, the system should be largely insensitive to orientation, at least for prime focus imaging.

Incidentally, reversing the corrector does not reverse the convergence/divergence action of any particular zone. The overall *shape* of the corrector as a lens is still the same, and ensures that the same basic wavefront shaping is occurring. It's only the difference *in detail* as regards the action of the asymmetric form at each surface which causes a bit of a departure from the ideal wavefront meeting the primary mirror.

Imagine a corrector which has both surfaces figured identically so that the 'workload' of wavefront shaping is shared equally. Such a symmetrical lens can be reversed and still work identically. Real world correctors are rarely if at all fabricated in this way, but even so still work mostly correctly when flipped around, again differing from ideal correction in detail, not fundamentally.

#16 droid

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Posted 04 January 2013 - 06:01 PM

Ok , most of the last three posts have been over my head, lol......but I adjusted the secondary mirror and with the help of my cross hair collimating eyepiece thingy, got everything really pretty, everything lines up in one circle, still and all , the secondary is over sized, I care not mind you , Ive used it for years out of collimation and it impressed me, and everyone else who looked through it.
Thanks for the help and advice guys, much appreciated.

#17 Bill Griffith

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Posted 05 January 2013 - 01:16 PM

For many years this was my RFT patiently waiting for my skills in collimation to be acquired.

New in 1985 for what else Halley's Comet. Celestron did some campaigning.

Yes, still in the herd.

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#18 Blake Andrews

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Posted 05 January 2013 - 01:21 PM

Beautiful mount. :jump:

Was it offered by Celestron with the Comet Catcher?

Blake

#19 Bill Griffith

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Posted 05 January 2013 - 01:38 PM

Thanks Blake.

Yes, completely original setup with a Polaris mount. The OTA has the .250-20 billet for mounting the OTA to a photo tripod. Oculars are a 18mm ortho and a 7mm ortho Celestron volcano tops.

Bill

#20 droid

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Posted 05 January 2013 - 09:33 PM

I had ofter wondered whether it came as a kit.
Now I know.....mine was a gift and was just the ota.
No eps or mount.
Doubt youll find that mount with the clam shell now a days.

#21 droid

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Posted 08 January 2013 - 10:16 PM

I did find one thing today ,that may be of interest to comet catcher owners, the dew zapper strap for my 120 refractor, is a good fit for the comet catcher too.Its an Orion brand dew zapper strap.And its orange to boot. lol

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#22 droid

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Posted 14 January 2013 - 10:22 AM

over in the best of files , in the reflector forums, there is a thread for collimating Schmidt newtonians, if I had found it sooner it would have explained a lot of what I was seeing. Im gonna post here for those of us who own these scopes, hope its ok.

http://www.cloudynig...2263887/page...

#23 StarStuff1

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Posted 14 January 2013 - 11:04 AM

Oddly enough, I have had 3 of these scopes and never have had to collimate a single one. One was new and, of course, 2 were used. The only major prob was dew on the corrector. But, easily solved:

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#24 droid

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Posted 14 January 2013 - 10:37 PM

Nice, Ive ofter wondered how many of the original orange tubes there are out there, rarely see any.

#25 Ducky62

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Posted 14 January 2013 - 11:12 PM

Thanks. I hadn't seen that thread.






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