Collimating my 4.5" f8 newt.

[ColHut]

Got my Orion Cheshire collimating thingy the other day and plucked up the courage to check out the collimation. Some of those stars just seemed to have tail. Read tons of helpful stuff on the web and they all roughly agreed but details were different. Was this important Scratch Scratch!. Okay the sight tube is a little short but the secondary really does look centred. Oh Oh Oh no centre spot. The instructions with the telescope have no information on how it comes apart. Luckily I discover that the back metal shroud actually pulls of the bottom (I thought it fixed). Behind are three large shiny knobs and no holding screw (so this means that for each give another must take...) Anyway undo another three small screws on the outside and the whole back comes off with the shiny glass mirror retained loosely on the other side by three screws and a circular frame. It really is barely 112mm never mind 114. Anyway place on bench and remove frame screws, remove frame, replace screws. I have a cunning plan. I get out my drafting compass place the point in the centre of each Phillips screw, set the length, and make three small arcs just visible in the centre if the mirror. they are crate a triangle about 1.5-2mm across. I get some cream packing paper tape and colour it black. I cut out a square 10 x 10 mm and fold it gently down the middle holding it diamond wise sticky side out. Oh how to place it on the spot as it is bigger. Ahah - cut out a tiny 2mm triangle from the folded square in the middle and it crates a tiny square through which I can see to centre it on the mirror. Greatly relieved I put it all back together.

Now I have no real idea what it was like before hand but now you can see that the centre spot is some way off. I point the secondary to centre this and then with my long arms stuff-around with the knobs of the primary (slacken one tighten one until Cheshire hole is lined up too. Voila. A quick check shows it a nice a tight, a win.

A note of frustration however. I need to wear glasses to collimate and trying to see through the pinhole is very awkward. We visually challenged need some way to fix this.
Anyway, The whole thing took about three hours of stress and worry but now I have done it will be much easier now I understand what to do.

Thanks to all those articles and go for it sentiments expressed in many collimation threads. Cheers Wol

[Geoff45]

An f8 scope is going to be quite forgiving of minor collimation errors. Forget the Cheshire eyepiece. Just centre the diagonal when you look down the eyepiece tube. (try to keep your eye centered--it helps to keep it back a bit). Then adjust the diagonal until the reflection of the main mirror is centered in the diagonal, then tweak the main mirror adjusting screws until the reflection of the secondary is centered in the main mirror.
When you've done this a few times, you may want to start using the cheshire again, but it probably won't make a lot of difference.
Geoff