Collimating without a tool

[Thiink]

Sorry about bringing this old thread back, but I have a question.

I've just been using a film canister for the moment until I get a chesire, and have found that the only way to get a good look at where the centre spot is, is to point the telescope outside during the day. If I try against a lit wall at night, or by shining a touch onto the roof it doesn't work as well. Anyone have any tips?

Also after pointing it outside (through the window), checking colimation and then looking at the primary through the top, I noticed that the sun was pretty damn close to where I had the scope pointed (could almost see it around the edges) it left me wondering how long you could do something like that before the secondary ends up damaged from the heat?

I really need that chesire!

[slice of heaven]

Thiink. I use a 'clear' film cannister . I leave half protruding from the focusser .The scope I place under the light and aim it at the ceiling near the light, not at it. The light shining on the cannister gives you better contrast on the hole and the white ceiling gives a nice background. Check your collimation at vertical, horizontal and at 45 degs. Take note of any change.

ps : To check how central your hole is,rotate the canister after coll. and see if the hole stays central or if it has an orbit.

Slice

[gaa_ian (Ian)]

Great article on centre spotting a primary mirror.
Sometimes the simplest things are the best !
It's been one of those questions in my mind too
I was thinking of measuring, etc ... So easy this way

[ballaratdragons (Ken)]

Simon,

Pointing at or near the sun will not damage your secondary at all.

It WILL blind YOU however!!!!!!!! Permanently!!!!!!!

Avoid, at all costs, pointing anywhere near the Sun. When I do outside collimating before sunset I point in the opposite direction of the sun just in case I move the scope slightly while checking collimation.

You will only ever make this mistake once. Blindness is a reminder.

[Roger Davis]

It doens't matter if your centre dot is out by a mm. It's only there to guide you! Once you have performed the collimation you will soon figure out that the dot "ain't quite right". Make a mask out of a manilla folder, give it three tabs that can sit on the retaining clips so that it doesn't touch the mirror surface. It will look like a trefoil so you can match the circumference of both the mask and the mirror. NOTE: the human eye is very good at centralising, you can collimate a telescope quite well without any tools, close enough that you can finish off with a star test. Other tools are great, but not always necessary. Longer focal ratio telescopes are quite forgiving!