Collimation with Cheshire - advice needed

[Sirius Bizness]

I am using a Cheshire collimating EP to check the collimation on my SW MN190. I can easily see the circle on the secondary lines up with crosshairs but I can't see the circle on the primary. My eyes focus on the cross hairs and secondary circle but won't see past. I am assuming that the reason I can't see the primary centre circle is that is is well collimated and directly behind the cross hairs. Is this normal or are there any tips to check?

I also can't see any clips on the primary so how do I know if it is centred?

I find it hard to check on a star due to turbulence so was hopping to nail it indoors first.

Any advise would be greatly appreciated.

[skir]

This guide might be of use:- http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

[Sirius Bizness]

Yes this guide is brilliant and what I have been using. I don't get why I can't see any mirror clips though. I guess the fact I can't see the primary centre spot means the collimation is spot on. I could always adjust the primary to throw it off and prove my theory.

[Astro_Baby]

Question.....what scope r u trying to collimate ?

Reason u may not see clips is the chshire may b 2 long, try pulling it out of the focuser a bit or try racking focuser right out.

Some scopes u cant see clips with ches. u ave to use a colli cap to see them.

Scuse txt am mobby.

[BuzzBomb]

Can we do away with the text talk please? Most annoying!

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[Gomtuu]

Don't know if it helps, but the following are from my SW 200PDS. One looking down the focusser, the other down the Chesire. It's a fast scope which is why the circles are not concentric when looking down the Cheshire.

[Sirius Bizness]

Thanks Astro Baby, that's a good tip and will give it a go. It's the SW MN190 which does have a very short focus travel and needs a 50mm extension for visual which I wasn't using for collimation. Think this may be why I can't see the clips.

Those pictures are helpful Gomtuu so I will do my own and post up for a comparison. How did you image down the Cheshire?

[Gomtuu]

Pictures taken with a snapshot camera - Panasonic Lumix. You need to hold it in just the right place over the Cheshire!

[Moonshane]

if your cheshire cross hairs are aligned with the centre of the doughnut (it's actually on the primary but reflected on the secondary) then your secondary tilt is correct. the mirror clips (if you even have any - not all scopes do) are another way of doing this but it's not necessary (in some scopes not possible) to be able to see the mirror clips using the above method.

I am presuming you have checked for a round face presented up the tube and that it's central in the drawtube of the focuser first. t

you may be right that you are seeing the centre dot actually already inside the doughnut and that it appears as a larger circle (i.e. it's collimated). tweak one of the primary adjusters and you'll know. if so tweak it back and you're done.

[JD75]

I'll be taking on my first collimation attempt this weekend as after a quick nose out when the sky cleared last night, I realised just how far out the thing is. The pictures here will be really helpful, so thanks for posting these. I have a few guides bookmarked too and planning a slow careful attempt at this on Saturday.

[crazyjedi]

Can we do away with the text talk please? Most annoying!

Sent from my GT-I9001 using Tapatalk 2

Ouch, a bit harsh! Whilst I don't use text talk myself it is easy enough to understand if used sensibly and some people find it much easier when tapping on a mobile. If you didn't understand part of it I'm sure Astro Baby would happily clarify. Surely not a reason to get annoyed though.

Back on topic. Good advice here. I will be following... Collimation isn't the easiest thing to get your head around. I have done it a couple of times but everytime I read a thread on hear I wonder just how accurate I'm being and if I have got it right.

[Gomtuu]

Even when I think my collimation is on the money, I always use the barlowed laser technique to check the final result and fine tune it. Of course, for that you have to have a central marking on your primary mirror, but it's a very simple and effective method. I use a misaligned and uncollimatable laser that I bought when I didn't know any better! At least it now serves a useful purpose.

[crazyjedi]

nice one Mark

[BuzzBomb]

Ouch, a bit harsh! Whilst I don't use text talk myself it is easy enough to understand if used sensibly and some people find it much easier when tapping on a mobile. If you didn't understand part of it I'm sure Astro Baby would happily clarify. Surely not a reason to get annoyed though..

I think the terms of use of this board state that all posts have to be in English. Text talk is NOT English and there is no need or requirement for it here.

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[Moonshane]

Please keep on topic guys.

[crazyjedi]

I'll be trying Marks barlowed laser method as soon as I get a chance. I've not heard of it before and it'll be interesting to see how accurate my previous collimation efforts have been.

Excellent tip

[Jason D]

I'll be trying Marks barlowed laser method

Barlowed laser method was invented by Nils Olof Carlin. I do realize Mark did not claim ownership of the procedure. I just wanted to clarify.

In addition, barlowed laser can only be used to adjust the primary mirror. It can't be used for the secondary mirror.

Jason

[crazyjedi]

All good info.

I seem to learn something new every day on SGL

[Gomtuu]

In addition, barlowed laser can only be used to adjust the primary mirror. It can't be used for the secondary mirror.

Jason

Indeed.