Collimation of a reflector - what's the easiest & most accurate method?

[Emuhead]

Hi all,

Asking what the best method is for collimating an 8" f/4 reflector. I have a 2" collimation laser, but rotating it in the focuser moves the red dot a fair amount on the primary, so looking for a way without using a laser, and trusting my eyes instead.

What's the best method given the above? Any experience with an autocollimator, or poking a tiny hole in a 2" cap, or is it better to use no tools whatsoever and just use a defocused star?

Thanks,

[billdan]

I bought one of these from Bintel a long time ago and it works well.

It has a peephole to ensure the secondary is centred in the focuser draw-tube.
It has cross-hairs so you can adjust the secondary collimation screws and get the primary donut centred.
It has the window to see the primary donut that is reflected back and you can tweak the primary collimation screws to centre the reflected donut.

I'm quite happy with it and its not expensive.

The best device to buy is the Cats Eyes Auto-Collimator but expensive.

[croweater]

+1 for Billdans' advice. Gets you very close. Then maybe a tweak with a star test to finish.
Cheers, Richard :)

[Startrek]

I use an Orion Cheshire collimating tool to align the secondary first and then the primary ( similar to billdan )
Then double check and tweak it with an Orion Mk11 laser collimating tool
I made up a V block to check that the Orion collimating tool was aligned out of the factory ( some aren’t)

[alpal]

Collimation is super critical at f4 but I found a simple way.
I put my laser into a Takahashi Barlow lens in the focuser and move the 3 adjustment screws
until I see the image of the paper reinforcement - at the center of the primary mirror -
reflected in the laser pointer screen.




cheers
Allan

[Saturnine]

Check your laser pointer, may have 3 grub screws around the body about 1/2 way along, if it does then you can use them to collimate the laser so that the dot doesn't make a circle if you rotate it in the focuser

https://www.youtube.com/watch?v=5ZsgNlgIrqQ

A Cheshire is still the simple way to align your optics, may take a few attempts to work out the process but once you do you will wonder what all the fuss is about. F4 does make it more fiddly though.

[Emuhead]

Thanks all, will go the laser & Cheshire route. My laser did have those 3 screws which I had to dig the rubber out of. So there's hope for it yet. I can't justify spending another $500 on a catseye package, because when you factor that in with a $500 coma corrector, might as well have bought an expensive refractor.

Cheers,

[Outcast]

I found this guide invaluable when it came to collimating a Newt for the first time.

I use a Cheshire & a laser but, this guide also covers just using a Cheshire.

Cheers

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

[Emuhead]

Very useful link, thanks for that. :thumbsup: