Laser Collimator - how accurate is accurate?

[kirkster501]

I think the slop on my focuser is the culprit. However, to check my collimator I put it in a V-block (home made thingy) and shined it at a wall six feet away. It moves slightly - about half an inch - when I rotate it in the v-block. Just trying to calibrate what in my mind is good enough. Is that good enough? Or should it not move at all? What if it was say 20feet away? Should it not move then either?

Rgds, Steve

[Tinker1947]

My Baader MkII, is stable at 12' when rotated through my Lathe Chuck, the shape of the Baader don't lend its self to a V Block, but the less movement the better.

[lennylovit]

+1 for no movement ,done on vee blocks adj till no shift over 15ft

Lenny

[John]

I agree with the other posters - I try and get mine to stay on the spot at 15-20 feet.

Your scope has a focal length of 1.5 metres and the laser has to do that twice so 3 metres. The collimation "sweet spot" of a F/5 scope is just 2.8mm so the laser collimator needs to be as accurate as possible.

[kirkster501]

Many thanks for you guidance and input. I will set to work and get it spot on.

Steve.

[Stargazer_00]

I use a HoTech SC collimator (FLO) The thing is precision encompassed. Never once regretted investing in a better priced laser collimator. Get perfect collimation in less than 5 minutes. It's a shaped lazer too so you can get the dot on the primary perfect (has diffraction spikes or something., cross with a dot in the centre). Used a lathe to measure it's accuracy and it's spot on the length of a standard garage.

[laser_jock99]

Not only does the laser have to be well collimated to the centre axis of the collimator, where and how you place it in the focuser matters too. Aim to have the target face around about your eyepiece/image plane distance (this might mean racking the laser outwards more). Also be aware that clamping the laser tightly in the focuser might move it off the centre axis of the focus tube (which is what after all you are trying to align the mirrors with).

[kirkster501]

Not only does the laser have to be well collimated to the centre axis of the collimator, where and how you place it in the focuser matters too. Aim to have the target face around about your eyepiece/image plane distance (this might mean racking the laser outwards more). Also be aware that clamping the laser tightly in the focuser might move it off the centre axis of the focus tube (which is what after all you are trying to align the mirrors with).

I use a 1.25 centering adapter for the 1.25 laser collimator. However the centering adapter in turn sits in the 2" focuser of my scopes and this in turn has "rattle" room inside the 2" focuser. So I wrap electrical tape around the 2" Outer diameter of the centering adapter to make it very snug inside the 2" focuser.

I am going to have a go at adjusting the laser collimator later this afternoon.

[Russty]

I use a 1.25 centering adapter for the 1.25 laser collimator. However the centering adapter in turn sits in the 2" focuser of my scopes and this in turn has "rattle" room inside the 2" focuser. So I wrap electrical tape around the 2" Outer diameter of the centering adapter to make it very snug inside the 2" focuser.

Good idea

[kirkster501]

Been having a devil of a job collimating my collimator. Ay one stage I got it spot on from 3.5m away and it only moved about a 1mm. Smugly i thought job done! I then though, let me tap it a few times to simulate it being in my bits box and then checked it again. Miles out!!! Doh... I now have it such that it describe a circle about 5mm is radius when rotated from 3.5m. Not good enough that I don't think. What a palaver! This is the collimator from Amazon, this one. I need to carry on and see if i can get it right. Will give it another hour later on.

People wax lyrical about this collimator but mine was not accurately collimated from new as first post above.

[kirkster501]

Ok done it I think with my "deluxe collimator jig" From 5m it describes a circle of about 1mm. I think that is accurate enough ?

Sent from my iPhone using Tapatalk

[Tinker1947]

I think 1mm is as good as it gets...

[John]

Thats pretty good. I'd go with that

Have you thought about trying barlowed laser collimation ?. It's less reliant on accurate collimation of the laser and tolerant of a slightly sloppy fit in the focuser:

http://www.astromart.com/articles/article.asp?article_id=827

Just a low cost 2x barlow is needed.

[kirkster501]

Thanks John - I will take a look. Heard about this before but never looked into it.

Steve

[knightware2]

Steve,

You haven't mentioned the focal ratio of the telescope(s) with which you use the collimator. The faster the scope, the more critical your collimation needs to be. My scope is f/4.5 and at about 5 feet, the collimation dot circumscribes about a 1mm circle. I say 'about' because it moves, but the distance is nearly immeasurable with a steel rule marked in millimeters.

Laser collimators should not arrive new out of collimation, but it happens. I suppose shipping jars them. What really concerns me is that you re-collimated the laser, tapped it, and it lost collimation badly. If that were mine, I would return it to the dealer for another, or return to the manufacturer for repair.

I use a 2" HoTech collimator with a 1.25 inch adapter. However, I found that the collimator + 1.25 inch adaptor moved too much in my focuser. When I collimate now, I use the 2" collimator in the 2" focuser - no adapters. This steadied up the collimator a great deal. I also tighten the set screws on my focuser just until they touch the body of the collimator, and then a touch more. This is how I insert 2" eyepieces while observing, so this is how I collimate. I use 1.25 inch eyepieces with the focuser's adapter, and I know the collimation is not perfect in this case. Star tests indicate it is pretty darned good.

I am rather fastidious with collimation since the focal ratio of the scope is 4.5. Thus, I follow laser collimation with CatsEye cheshire (rarely disagrees with laser) and finally a CatsEye Autocollimator. The autocollimator always results in adjustments to the secondary holder, so I feel it is a critical final step.

I have a slower telescope (f/7.6) that I collimate with a mechanical cheshire (no laser). I rarely use an autocollimator with this scope.

Good luck with the laser. They are terribly convenient!

[kirkster501]

Its a 300 Dob @ F4.9 but I will also use the LC on my other scopes as well. But the dob is the one I am using it on first. When I tapped it and it shifted before, I don't think I had the three screws equally tight. Two were tight and one loose, hence losing the collimation. So I had to loosen them and redo in such a way that all three screws were equally tightened. Sounds obvious but when you are trying to get the dot central you can overlook these things !

Steve