collimation question

[Bungielad]

Hi there....

just a quick question....whilst looking through my cheshire eyepiece I see the doughnut exactly in the centre of the cross hairs but the black dot not centre and down to the left.Am I correct in saying that the primary is ok and the secondary mirror is out? If I try to get the black dot and doughnut in line with the centre of the cross hairs by moving the primary then both do not line up with the cross hairs. Help please.

bungielad.

[andyman]

dont own a cheshire only a laser but the method should be similar start by lining the secondary first to the primary then adjust the primary mirror so everything is inline some one more experienced will be along shortly to advise

[Bungielad]

Sorted....was secondary out! 1st time iv done the whole collimation and cant say getting the secondary in place is an easy thing but got there in the end.....its the best collimated since iv had it.

Bungielad.

[Moonshane]

the process is :

1) check vanes are equal and central, and that the secondary holder is central (adjust with the vane attachments)

2) check that the secondary is round in the focuser and central to the drawtube (adjust with rotation of the secondary and by screwing the secondary central bolt in our out to move it up or down the tube)

3) check that the (fuzzy) cross hairs of the sight tube/cheshire are central on the reflected donut on the primary (adjust with secondary screws)

4) centre the dot of the sight tube/cheshire in the donut on the primary (adjust with the primary adjusters).

you must work in this order (although 1) and 2) might be OK and never need doing) or you'll not be properly collimated. eventually you'll just need to tweak the primary before each session (or not at all).

from your initial post it sounds like you were OK to point 3) but needed to do point 4). as you have now undone point 3) I'd start there again assuming your secondary is round and central in the drawtube.

you'll eventually just click and wonder why you ever struggled!

[Bungielad]

I have a near on perfect circle of secondary in focus tube with and without the Cheshire, both doughnut and black dot are perfectly alighned in the centre of the cross hairs, I found that moving the secondary with hand helped alot ( obviously without touching the mirror) also just using my eye without the Cheshire at first also helped to get a rough alignment and then using the Cheshire to perfect it, took me a good 45min to get there and hopefully when I go out next it will show as a good result........hopefully! !!

Bungielad.

[Moonshane]

I am sure you'll be fine as one way or another it sounds like you have it well collimated. as you do it more frequently, it will become easy.

[Bungielad]

Thanks for the guidance moonshane, much appreciated.

Bungielad.