Quick collimation question

[Adz]

Hi guys,

Probably a really simple answer for someone.

I am collimating my scope, firstly with a cheshire. So I have got the secondary as a perfect circle in the middle. Now onto adjusting it so the 3 primary clips are visible?

After I have done this, the secondary is good to go? When I come to whack in my laser (which shows me is collimated in my jig) the laser doesn't hit the centre dot.

Why is this?

Thanks

[Merlin66]

The laser is out ;-)

let the force be with you - trust your cheshire -

The final test should be with a star image - it will show which one is best....

[Adz]

Thanks Merlin.

So in theory I could collimate my laser by getting it all perfect with a cheshire, and then tuning the laser to point to the middle dot...?

So much for my home made jig I guess I shouldn't consider a home made scope build!

[inksmithy]

Do a little search on Google for the Barlowed laser technique, it doesn't rely on a collimated laser, where the normal method does.

I just started using it on my dob and its made a massive difference to the time I spend collimating, not to mention the diminished fear factor.

Alan

[Adz]

Wait so when you place a barlow like the one I just bought, inbetween the laser and focuser. It doesn't have to be collimated on a jig!?!?

[Adz]

I wish someone that lived close to me knew about collimation

[inksmithy]

Did you do a search for that technique?

Essentially,m what you will end up doing is projecting an image of the centre dot back up along the focal plane towards where thelaser is originating.

Because it has come through a barlow, it is no longer a laser, it has been diffused to a splotch of light. Because you are no longer collimating based on where the laser points its light, but instead are basing your collimation on the image of the center donut you are projecting towards the focuser.

Really, do a search for the barlowed laser technique, it will make your life so much easier.

Alan

[Tim]

I'd do as Ken says for now, use the chesire, but check against a star Use polaris if you can, you will soon see if the collimation is out that way.

Lasers are a tricky beast best used for rough and quick, enhanced a lot by the barlowed technique. FWIW I use in this order:

Collimation cap, hotech laser, chesire, hotech laser, chesire, star test.

Cheers

Tim

[Adz]

Thanks for the replies guys. Yes I did do a search and read about barlowed collimation. But I couldn't find anything about whether the laser needs to be collimated or not, only that it eliminates focuser slop.

It probably doesn't help that my laser is tosh, and doesn't even produce a dot. So I tried modding it with tin foil to makeshift produce one.

Finding a star, let alone Polaris in this weather and light skies is difficult for me and my light pollution. But I am not trying to make excuses Cannot wait for winter skies!

I shall have a go with collimating the primary with my dad, because of the length of my OTA, its a two man job with the cheshire.

[Adz]

Well I feel like an idiot.

After my dad helping me, we tried the primary mirror fixing and adjusting screws. I was trying them the wrong way round! Adjusted the primary mirror to completely central in seconds by using the allen key adjusters! Then stayed in place with the cross head screws tightened up.

Trouble is, astro babies guide says they are the other way round...!?

Astro Babys Guide to Collimation