collimating in the dark

[iamjulian]

Hello

After bringing my scope home in the car from its summer holiday, I was amazed to see how far out of collimation it was. Took just a few minutes to fix with a Cheshire, but I started wondering how people get on collimating at night - at a dark site after the scope has been bounced around in the car.

I did a few google searches and most people say that while possible with a Cheshire, a laser is the way to go at night. Makes sense, but then a lot of people say that defocusing on a star should also be done after you have used the laser.

Reluctant to buy a laser, can I not just use a defocused star as a low tech way of checking collimation in the dark? Surely that's about as accurate as it gets? Why does everyone buy lasers if collimation is possible using noting more than the telescope a bright star? What am I missing?

[yeti monster]

A laser will allow you to check your secondary alignment before you align the primary. Without a laser you can align your primary on a defocused star and hope that your secondary has remained undisturbed.

[jimmyjamjoejoe]

Out of interest, how far out of whack is a scope likely to get from a short journey in a car on relatively decent roads? (ie no speed bumps or gravel tracks etc)

I don't have a scope yet, but i'm looking for around and 8" dob, and my dark sky spot is about 20-30mins drive away... Am i likely going to need to collimate every time i get there?

[Daniel-K]

i take mine to my local astronomot meeting weekly and i have to go over speed bumbps and some serious craters and mine just needs a tweak as long as its secure it shouldnt go out too much mines a 8inch newt

[yeti monster]

That's a short as it is long.

I once transported my 10" SNT 30 odd miles in the back of my Land Rover, where every tiny pothole and ridge gets magnified by the road springs. At the end of the journey it was but a tweek out.

Conversely, moving the scope 100 meters or so on a sack truck, trying to be careful, it was knocked for six and took a lot of fiddling to bring it back into alignment.

So it is best to be ready to do a full recollimation, that way if it is still ok, you are quids in.

[Merlin66]

I've moved all over the world with various scopes for the last twenty years.....I only collimate either when I get a new scope to play with....or get really, really bored.

At night you use a star test to collimate. Out of focus doughnut - wave your hand around the aperture to see which direction you need to move the secondary, find the nearest screw - twiddle - check - try the next - job done!