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Cap collimation

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#1 StarTrooper


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Posted 18 November 2019 - 06:58 PM

Knowing there are three techniques of collimation, laser, cheshire, and cap I like to keep things simple with minimum amount of tools to lug around. With that in mind is it possible to become very efficient only using a collimation cap? Can this procedure be done at night?


I did not forget the star test as one of the procedures.


thank you.

#2 Vic Menard

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Posted 18 November 2019 - 07:10 PM

For the record, a collimation cap is a Cheshire derivative--both align the primary mirror (as does star collimation). I assume by "Cheshire", you mean the ubiquitous Cheshire/sight tube combination tool. 


You can read about the various alignment signatures that ultimately define Newtonian collimation here  https://www.cloudyni...dobs/?p=4651500


The basic sight tube is about the only tool that doesn't work well at night. And lasers are the only tools that work at night without additional illumination--Cheshires and autocollimators get their illumination from low intensity red LED flashlights that are either handheld or clip-on.

#3 Kipper-Feet


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Posted 18 November 2019 - 07:55 PM

JESHEA, please check the Inbox of your Personal Messenger, you have mail.

#4 desertstars



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Posted 20 November 2019 - 03:58 PM

I've been using a collimation cap to touch up collimation for 15 years on an f/5 scope. For visual observing it's worked just fine.


If I need to collimate after dark, I use a laser collimator.

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#5 MikeTelescope


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Posted 25 November 2019 - 04:34 PM

I have a Lightbridge 12" like yours, and I've tried collimation cap, shorty Cheshire, long Cheshire sight-tube combo, laser collimator (with and without barlow), and star collimation on Polaris. 


After weighing the pros and cons, I use a collimation cap if there is enough daylight, or the shorty Cheshire and red light shining to the side into the cut-out if it is too dark.  Then I touch it up if necessary on Polaris.  My results have become much more consistent and are achieved in a shorter amount of time.  I have abandoned the laser collimator all together. 


On the Lightbridge, I put colored rubber bands on two of the trusses so that I put the same trusses in the same slots each time.  Then I tighten the bottom and top screws in the same order each time.  I have found that by doing these two things, the amount of work I need to do to collimate each time is significantly reduced.


I replaced the stock primary springs with some stiffer ones, and this goes a long way to keeping the collimation for the whole session and allows minimal movement when transporting the scope. 


Also I tightened the screws that hold the dark metal lip of the top and bottom tubes.  They were slightly loose, and as the scope changed altitude, the flex in those loose connections was a major source of de-collimation.  Two minute job that improved the consistency of the scope a lot. 

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