Collimating a Newtonian

For those who need help choosing a setup or want further advice on how to improve their own setup
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rwilkinson
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Re: collimating a Newtonian

Post by rwilkinson » Sun Mar 25, 2012 6:56 am

I've got our "Cheshire eyepiece" collimation tool at the moment:
http://www.boltonastro.org.uk/forums/vi ... f=17&t=112
I'll fetch it along to Sharples on Tuesday evening if you'd like to borrow it.

SkyWatcher's own 2-page guide to collimation is quite good:
http://telescopesandbinoculars.co.uk/ac ... IANNEW.pdf
and you'll probably find that your primary mirror has a black target-ring in its centre, to make setting up the secondary alignment (figs. d & e) even easier - just get this on the cross-hairs in the Cheshire eyepiece and then proceed to setting up the primary.

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DRatledge
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Re: Collimating a Newtonian

Post by DRatledge » Sun Mar 25, 2012 1:19 pm

Seeing the circle in the centre of the main mirror does not mean you are collimated. Judging by the stars you are way off. You need to see your eye or the hole of the film canister INSIDE the circle on the mirror.
The society has a laser collimator but unless you really really really know what you are doing will probably make things even worse! You have to start with these by adjusting the focuser to get it dead-on square so the laser dot will hit the centre of the circle. You may not be able to adjuct the focuser and skipping this stage is a recipe for disaster. I've given up using lasers - much too complicated - stick with the cheshire or film canister.

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Re: Collimating a Newtonian

Post by rwilkinson » Sun Mar 25, 2012 4:11 pm

poconnell wrote:I have been looking at the Antares Laser Collimator, what are your thoughts on these laser versions over cheshires?
We also have one of these: http://www.boltonastro.org.uk/forums/vi ... f=17&t=113
but see David's comments - I agree that a Cheshire will get you to the right result more easily.

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DRatledge
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Re: Collimating a Newtonian

Post by DRatledge » Sun Mar 25, 2012 8:46 pm

Phil,
Remember its the reflection of your eye, or the hole in the film canister, that you need to see inside the ring on the main mirror. That means everything is on axis. The secondary, being flat, only really effects vignetting.
We'll sort it Tuesday.

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Re: Collimating a (quasi-)Newtonian

Post by rwilkinson » Tue Sep 25, 2012 6:39 am

I've just encountered a strange hybrid telescope - it looks like a short-tube Newtonian, but has a sort of Barlow-lens fitted in the bottom of the draw-tube to extend its focal length.
With this type, it's impossible to collimate it by looking down the empty draw-tube unless the lens is removed; fortunately it just unscrews:
newtcolli1.jpg
Unscrewing the lens from the bottom of the draw-tube.
But first tilt the tube so that if it slips out of your fingers it won't drop onto the primary or secondary mirrors!
newtcolli1.jpg (143.95 KiB) Viewed 8516 times
newtcolli2.jpg
Put the lens to one side whilst you complete the collimation.
newtcolli2.jpg (165.61 KiB) Viewed 8516 times
The collimation adjustments are summarised in this two-page guide from SkyWatcher:
http://ca.skywatcher.com/upfiles/en_dow ... 546623.pdf
but this tutorial from AstroBaby gives full details of how to set everything up from scratch:
http://www.astro-baby.com/collimation/a ... 0guide.htm

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