Newtonian Collimation

[Sparrow]

I've seen the previous thread on here by Lguise about how to centre spot the primary - didn't want to hijack the thread so I've posted myself:-

This may be an exceedingly daft question but how do I reach the mirror to mark it? - I presume I've got to take it out at the base of the scope to do this which means it's going to need collimating anyway when I put it back together.

Also, any recommendations on which collimator is the best for the job (Celestron 8" Newt)

[Deneb]

There should be a round sticker in the centre of the mirror, regarding a laser collimator, Checkout FLO & buy a Hotech Laser Collimator.

[Astro_Baby]

My recommendation would be to get a Cheshire

A laser cant do alignment of the secondary to the focuser. A cheshire can do the lot and so many people have problems with lasers - me included.

The Hotech is the only one I liked but its expensive and chances are at some point you'll need a Cheshire to do the secondary alignment.

[nitram100]

Unless you can get hold of a laser collimator that can be collimated itself, i wouldn't bother personally as the laser may be out of collimation.

I bought a laser collimator last year and it was awful, it was so out of collimation it was laughable so i just bought an Astro Engineering chesire instead and it works a treat and Astro_Baby says, you can also align the secondary using a cheshire.

As for marking the primary, this is the method i used and it worked perfectly. http://codeidol.com/other/astronomy/Scope-Hacks/Center-Spot-Your-Mirror/

[yeti monster]

When I took out my primaries to clean them and add the "donut", I found the centre of the mirrors using a straight edge and a fine marker pen. To apply the "donut" I used one of McDonalds coffee stirrers with the "donut" lightly stuck to the end. I found this to be the easiest way of positioning it with the marked centre directly at the centre of the "donut". The faint marker was then cleaned off using isoprpyl alcohol, although I'm sure this can be left.

A cheshire collimator will be handy though, as I can only do "field collimations" atm.

[albedo0.39]

A cheshire collimator will be handy though, as I can only do "field collimations" atm.

You might be interested to know that many people report that in the right hands, a cheshire is the most accurate collimation device on the planet... despite the clear convenience of a laser. I read a very complex white paper that talked about a barlowed laser coming close, but I've no experience. So, I think you can get all you need right now from the humble cheshire

Cheers

[themos]

Remember, the centre of your primary is in the shadow of the secondary and it does not contribute to the final image. This means you don't need to worry about fingermarks, coatings, scratching etc

[John]

You might be interested to know that many people report that in the right hands, a cheshire is the most accurate collimation device on the planet... despite the clear convenience of a laser. I read a very complex white paper that talked about a barlowed laser coming close, but I've no experience. So, I think you can get all you need right now from the humble cheshire

Cheers

Thats my experience - I've tried 2 laser collimators (including the Baader ) but I could not get on with them so I'm now using a cheap plastic "Cheshire" eyepiece which works great - with final tweaking performed under the stars.

John

[Sparrow]

Thanks for all the replies everyone - much appreciated

So a Cheshire Collimator it is then - not a bad price from FLO.

BTW - I'm delighted to say that in their wisdon, Celestron have already put a donought mark on the primary - excellent - really didn't fancy having to take the primary out with it being so new.

This forum really is the business when you need help on something - my sincere thanks to you all.

John

[Astro_Baby]

For anyone ele wondering how to centre spot - read the instructions on the CatsEye site for getting their red marker onto the primary. Its brilliantly simple and would work just as well with a paper reinforcing ring.

Have a practice because their instructions are kind of counter intuitive but you'll see its a brilliant way of doing it.