Laser Collimation Guide for Newtonians

[Mr Spock]

There's a lot of hype and fear surrounding the collimation of Newtonians. While there are many different ways of achieving collimation, the laser is probably the simplest and quickest. My 12", used here as an example, usually takes less than 30 seconds to do!

At this stage I will assume your secondary is aligned under the focuser. Most scopes come with it near enough, but it may need adjustment. I do this with a concentre, but there are other methods. But remember, as long as the optical train is aligned, small differences in the position of the secondary don't matter. In most cases I would advise leaving it alone as you can get in a real tangle real quick!

What if my laser isn't collimated? This can happen - some of these are put together very cheaply. I think when I bought mine it cost about £20... If it's not collimated you can either send it back as unfit for purpose, or adjust it yourself. There are three adjustment screws near the top usually sealed in. You can remove the sealant to get to the adjustment screws. I've never had to do this and my laser is spot on. There are a number of YouTube tutorials on how to do this.

Checking laser collimation.
Nothing fancy required. Just aim the laser at a wall some distance away, rotate the laser to see if the spot on the wall moves. The wall should be at least 2 metres away and the movement at that distance no more than +-2mm.

Placing the laser in the focuser
Any play in the laser/focuser interface can affect collimation accuracy. Use exactly the same method you would use for a high power eyepiece. Don't use the included 2" adapter as this will have different play to your normal eyepiece adapter. Remember, the aim of collimation is perfect alignment of your primary, secondary and centre of your eyepiece.

Adjusting the secondary

The laser should be pointing to the centre of the primary's doughnut. Here it is not...
Note on these images there is some flare from the laser due to the mirrors fogging - this is because I brought the scope indoors and didn't have the patience to wait for them to clear!

Adjust the secondary using its adjustment screws. Note: I have replaced mine with Bob's Knobs for ease of use.

When you have done adjusting the screws - remember, only small movements at a time and keep the tension on each equal - the laser should point to the centre of the doughnut.

Adjusting the primary

The laser should 'disappear' down the centre hole of the collimator when aligned. Here it is not...

Adjust the primary knobs. Same as with the secondary, keep the movements small and the tension equal.

Adjust the knobs until the laser disappears down the centre of the collimator.

And that's it! We're done! You can make more critical adjustments using a star test but I've found once I have done this with the laser my scope doesn't need it. Being able to pick up fine detail on the moon at x461 in excellent seeing shows how accurate the collimation is.

 

[Captain Scarlet]

Good quick guide.

Some people suggest that for visual, the need for accurate collimation is exaggerated. I strongly disagree, and unwittingly demonstrated this to myself a couple of weeks ago.

I collimated my 12” in my usual way (using a tublug rather than just a laser but that doesn’t alter my point). I got on with observing, and noticed that everything looked far worse than I’d been expecting. I put it down to poor seeing, but just in case I pointed to a bright star and immediately saw the classic “pointy stripy oval” shape indicating bad coma. Very odd.

I put the tublug back in and it seemed ok. I then rotated the tublug in the holder and the shadow started to move in a circle across the angled tublug screen! Something wrong with the collimator! I actually have two tublugs, so I put my other smaller 1.25” in, and it showed collimation to be out, by half the width of the angled screen, i.e. seemingly not grossly. I centred this shadow, and it stayed put when I rotated it. Subsequent star test showed all good.

Next day I inspected the errant 2” tublug and found the angled-face insert to be loose, so it had been at a random angle.

Anyway, my point is that even with the return shadow/laser dot only halfway away from “disappearing down the hole”, the view produced was noticeably poor in an f/5.4 (6.2 with paracorr) Newtonian. Poor enough for me to have considered abandoning the session had I not fixed it.

Magnus

[Mr Spock]

Indeed. I cannot emphasise enough how important it is to have collimation spot on. Near enough isn't good enough. Even a smidgen out will blur detail.

[PeterC65]

It's good to see the process of collimation explained so simply.

I agree completely that anything other than fine pointing adjustment of the secondary can be rather stressful. I find that the secondary rarely needs adjusting, and all I need to do for each session is perform a minor adjustment of the primary, making sure that the laser disappears into the hole in the centre of the target.

I have the same laser collimator as you and it's worth mentioning that you should orientate the target so that it points towards the primary end of the tube, then even on a big Newtonian you can stand at the primary end making fine adjustments while seeing the laser on the target.

 

[John]

17 minutes ago, Mr Spock said:

Indeed. I cannot emphasise enough how important it is to have collimation spot on. Near enough isn't good enough. Even a smidgen out will blur detail.

Agreed and your guide is great 👍.

Slight Mis-collimation has even more impact with SCT's I believe.

 

[bosun21]

These are the same steps I take when using a Hotech laser to collimate. I use the 2" version to eliminate any slight misalignment discrepancy with the addition of a 2" - 1.25" reducer. I can collimate my scope this way then completely remove the laser and insert it back in with a different orientation and it's still perfectly collimated. I haven't really had to adjust the secondary very much at all apart from the tiniest tweaks, and even then rarely.

Edited December 23, 2023 by bosun21

[Gonariu]

A question: can you collimate a Schmidt-Cassegrain with the laser collimator for a Newton?

[Mr Spock]

1 hour ago, Gonariu said:

A question: can you collimate a Schmidt-Cassegrain with the laser collimator for a Newton?

I've only ever collimated an SCT using a star test. This is the process I used for my C9.25  https://www.celestron.com/blogs/knowledgebase/sct-edgehd-collimation-guide