Author Topic: C90 collimation  (Read 285 times)

James Bagby

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C90 collimation
« on: December 24, 2017, 03:12:19 AM »
I've been told that the c90 will never require recollimation.  I've got one that seems somewhat off.  Do the 3 screws at the back have anything to do with collimating the range?



handthedemo

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Re: C90 collimation
« Reply #1 on: December 24, 2017, 05:27:30 PM »
<p>
Quote
</p>
Do the 3 screws at the back have anything to do with collimating the range?
Yes.  But if you do not know just what you're doing and the extent is only a bit off, I recommend taking it easy, read up on star testing and collimation for a few months, seek advice from people, who have collimated their own C90's, browse for a few extra weeks, and only then try a collimation.  It might just require a *very* small tweak and there's great risk that you'll ruin the extent completely, if you do not know what you are managing.

Just a friendly advice.Clear skies!
Thomas, Denmark

heanestucap

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Re: C90 collimation
« Reply #2 on: December 28, 2017, 11:39:08 PM »
Is this an old orange C90 or a new C90?

ryepittimy

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Re: C90 collimation
« Reply #3 on: January 03, 2018, 07:52:12 PM »
If it is one of the early orange ones where focusing is by rotating the front section of the tube carrying the corrector, most of them varied the collimation as they turned.

Jeremy Butler

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Re: C90 collimation
« Reply #4 on: January 07, 2018, 09:58:19 PM »
Yes, it's an older orange one!

cytiwitqua

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Re: C90 collimation
« Reply #5 on: January 09, 2018, 07:59:26 PM »
Astrojensen's advise above is agreed with here. Many claim that the collimation is fixed at factory with epoxy/rtv &amp; shouldn't be tampered with. There are also claims that the three factory screws on the back are merely hole plugs &amp; are too short to have any effect, but there IS one member's claim that their's had slightly longer screws and was able to witness changes in their collimation when tweaked. It was a very early model/serial number however, and the ability to adjust collimation may have been abandoned early on during production. They might have foreseen lots of customers playing around with them, blowing out their collimations &amp; then requesting warranty repairs  A cautionary note in the manual would have gone a long way in that regard, but I've yet to witness one.

Again, I'm on the side that says 'Don't Touch' even though the temptation is Very real.

Hope this helps.

russnappditcva

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Re: C90 collimation
« Reply #6 on: January 09, 2018, 10:57:59 PM »
I don't believe there are any collimation screws on the old C90. I don't remember any on mine.

statfuncteeci

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Re: C90 collimation
« Reply #7 on: January 10, 2018, 07:04:31 AM »
Well, I stand corrected. Apparently there WAS a word of warning in the manual. See page 13 in the pdf link below:

<a>https://drive.google...iew?usp=sharing[/url]

trapoutampub

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Re: C90 collimation
« Reply #8 on: January 11, 2018, 03:45:15 AM »
Linky no worky.

coepupinsynch

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Re: C90 collimation
« Reply #9 on: January 11, 2018, 04:06:37 AM »
I have had a few of the original C90s and the screws in the rear cell were just plugs. What they were for I was told was during initial assembly they used longer screws to set the tilt of the primary until the rubber adhesive cured. Putting in a longer screw now while rubber has cured will likely give astigmatism or if over tightened a lot might even chip the mirror. If you do try that route, use nylon screws and just fingers to try to tweak it a bit without over stressing anything

The set screws on the sides of the front tube are holding little wedges that hold the corrector in place. With a lot of trial and error you can tweak things a little by loosening aone and tightening the other two which very slightly shifts the corrector and secondary sideways but could never get one perfect, since the whole front rotates to focus.

Dave

dextcinthrervest

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Re: C90 collimation
« Reply #10 on: January 11, 2018, 02:03:27 PM »
Quote
I don't believe there are any collimation screws on the old C90. I don't remember any on mine.

The old C90 were on or Off. I don't think they were originally designed for high enough magnification to worry about spot on collimation.
Enjoy it, love it, they are great scopes, it probably needs the screw barrel re-lubed.
There is a hidden screw under the tripod mounting plate, that stops the front barel from unscrewing and falling to the ground.
White Lithium Grease works best.
Good luck
PM me if you need any further help
Duane

propdiagairil

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Re: C90 collimation
« Reply #11 on: January 11, 2018, 05:59:51 PM »
Quote
Linky no worky.

Hmmm...Thanks for pointing this out, Don.

Let's try this:
https://drive.google...kQ3NU5VbG8/view

Jason Kaltwasser

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Re: C90 collimation
« Reply #12 on: January 12, 2018, 07:04:07 PM »
Agreed, I think the gease may have more impact on collimation than anything other than using the OTA as a football.

adectisun

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Re: C90 collimation
« Reply #13 on: January 18, 2018, 12:59:59 AM »
I have an old orange C-90. The mirror is glued in place! The three screws in the back are plugs to fill the holes where the factory collimation screws were inserted prior to the mirror being glued in place. The mirror is quite thin, since it doesn't have to be self-supporting. Inserting a longer screw to try to move it will likely do fatal damage to the mirror.

Many of the C-90s from the mid 1980s are poorly collimated, mine included. I have heard of one person successfully recollimating his C-90. He opened the tube up and rotated the baffle tube 180 degrees. Apparently that fixed the problem. I have had mine open to re-grease the focuser, but haven't had the nerve to try fiddling with the baffle tube.

To open the tube, unscrew the tripod socket on the bottom. Hiding under the tripod socket are a pair of set screws that are the stops for the helical focuser. Remove the screw closest to the aperture and you can unscrew the entire orange part of the tube, giving access to the interiors of both parts.