Collimation.....again..

[onmehedson]

I bought a cheshire to collimate the scope with. I have successfully manage to align the primary within the secondary, even got the donut and the reflection of the chesire bang on. So when looking down the focusing tube everything looks nice and centered.

But when i look at the mirror set-up down the cheshire, the crosshairs at the bottom of collimator are slightly off center with the center donut, just a tad higher.

Will this difference affect performance? If so how do I adjust the mirrors to get the crosshairs centered?

[kniclander]

i don't think that matters - it just means that the x-hairs on your cheshire are not perfectly centred i think:icon_scratch:

[LukeSkywatcher]

i don't think that matters - it just means that the x-hairs on your cheshire are not perfectly centred i think:icon_scratch:

I'd go with that. Once everything looks centred (mirrors,donut).....you should be fine.

[onmehedson]

Thank you kindly guys!!

Just like to add that collimating with a cheshire is easy peasy lemon sqeazy.....

[eyespy]

I agree, cheshires ...a big thumbs up from me

[Pete Presland]

Thank you kindly guys!!

Just like to add that collimating with a cheshire is easy peasy lemon sqeazy.....

easy peasy lemon sqeasy it drives me mad,i am never confident i have got it right.

i fitted a new focuser to my orion 10" newtonian after 1 1/2 hours i think i am close,but there is just too many things to look at through the cheshire.

i am thinking of getting a laser but i have heard they are not as accurate,but it might give me an idea of how close i am.

[kniclander]

easy peasy lemon sqeasy it drives me mad,i am never confident i have got it right.

i fitted a new focuser to my orion 10" newtonian after 1 1/2 hours i think i am close,but there is just too many things to look at through the cheshire.

i am thinking of getting a laser but i have heard they are not as accurate,but it might give me an idea of how close i am.

the pursists will scream at this but if its the secondary that's causing you grief, you can get away with a little inaccuracy there so long as you don't mind a little light loss. Then when you have enjoyed the scope a bit, you can spend three days obsessively getting the 2ndary just perfect

[Astro_Baby]

I'd say never get overly obsessive with collimation. As good as you can get it and a star test is fine. Trying to get all elements absolutely perfect with bulk made telescopes is the highway to madness.

Remember once your out in a cold dark field lots of things will affect 'perfect' collimation - the tube will flex depending on its attitude, the tube will flex from heavy eyepieces being used, the focuser will have some slop and at the end of the day your looking through 140,000 feet of goo which is the atmosphere.

Soooo get it right - but dont get mental about it.

[Pete Presland]

I'd say never get overly obsessive with collimation. As good as you can get it and a star test is fine. Trying to get all elements absolutely perfect with bulk made telescopes is the highway to madness.

Remember once your out in a cold dark field lots of things will affect 'perfect' collimation - the tube will flex depending on its attitude, the tube will flex from heavy eyepieces being used, the focuser will have some slop and at the end of the day your looking through 140,000 feet of goo which is the atmosphere.

Soooo get it right - but dont get mental about it.

i think i read that same advice somwhere on somebodys website!great step by step tutorial by the way

i followed it exactly-ish it certainly is better than it was!

the real test comes in about 2 1/2 hours outside,but surely the only adjustment possible if the field is the primary mirror?

[Astro_Baby]

Yes - out under a sky you should only mess with the primary mirror. The secondary (assuming its circular to the focuser and aligned) should almost never need to be messed about with.

[Pete Presland]

Yes - out under a sky you should only mess with the primary mirror. The secondary (assuming its circular to the focuser and aligned) should almost never need to be messed about with.

i will let everybody know how it goes,fingers crossed

[Pete Presland]

well did the star test last night before it clouded over seemed to be a reasonable concentric airy disc as described in the superb astro baby guide but no concentric rings,all i could see was the shape of the spider.

is this normal and was regulus too bright an object to use?

sorry if this sounds like an obsession

[Astro_Baby]

Did you see a sort of polo mint shape - ie like a large thick doughnut with a dark centre ? If you did that was probably all you would get.

To get a decent airy disk you need very high mag, perfectly cooled scope and usually perfect seeing conditions. I think I have only ever managed to see the classis airey disk pattern a few times myself.

[Pete Presland]

i used a celestron 7mm ortho,there was no doughnut just a opaque disc with a shadow of the spider on it

[Astro_Baby]

Sounds like focus was pulled too far back - you need to focus on a star and then gradually defocus until the doughnut/airy disks appear.

[Pete Presland]

thanks astro_baby will give it another tonight