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Collimator help

johnkirkpatrick

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johnkirkpatrick

johnkirkpatrick

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I have just received a Revelation Astro laser collimator, and am going to collimate my 5" Newt Astromaster 130.

1, How do I check my tool is correctly collimated before I use it?

2, then which way do I have it facing in my scope??

I have it in as we speak and the laser on my large mirror at the bottom of the scope ( primary/secondary???) is not in the centre and the laser on the actual collimator is not centred either?

very confused and worried I may make things worse.

Any help would be great :)

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johnkirkpatrick

johnkirkpatrick

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Hi thanks, I have it in and the laser is fine till i look at the laser on the collimater its a about 1 1/2cm off centre spot. but if i rotate the collimater 360 in the ep holder the laser beam changes position on the collimater by quite some bit. it looks more center facing the top and looks further apart facing the bottom of scope?? man i hate this lol

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Astro_Baby

Astro_Baby

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Ummm guys - my guide doesnt cover lasers because I just plain dislike them.

The easy way to check the lasers collimation is to roll it in a kind of L shaped bracket and see where the beam points. Thats harder than it seems cos most lasers dont have a smooth profile.

I'll leave it to a laser user to advise - personally the only one I used which I rather liked was the Hotech laser but thats a bit upmarket.

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steppenwolf

steppenwolf

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Your laser looks all but identical to mine and I only adjusted the three 'opposing' screws - I have no idea what the 'fourth' one is for. Remember that you MUST undo one and then tighten the other two to get a result and only make the tiniest adjustments.

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steppenwolf

steppenwolf

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If you are satisfied that the collimator is collimated and that it is a snug centre fit in the EP holder then it is time to adjust the secondary mirror until the laser is in the centre of the primary. Once this is accomplished, part two is to adjust the primary until the return beam is in the centre of the laser target on the collimator itself - i.e. the laser disappears up the hole from which it originally appears!

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acey

acey

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if i rotate the collimater 360 in the ep holder the laser beam changes position on the collimater by quite some bit.

You've discovered why lasers are so unpopular. The problem is "focusser slop", the laser is not an exact fit in the focusser, and there's enough play to create very large errors.

One solution is to use a Cheshire instead (keeping the laser only for secondary adjustment, which it's good at). Another is to use the barlowed laser method:

http://www.cameraconcepts.com/barlowed%20laser%20collimation.pdf

A third option is to get an all-in-one barlowed laser or similar device that claims to overcome focusser slop (as I believe the Hotech is claimed to do).

The cheapest is option 2 (if you have a barlow). After buying 2 lasers and finding them both useless for primary collimation I went for option 1.

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Astro_Baby

Astro_Baby

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Persoanlly I dislike them - I found the two I tried eneded up causing more problems then they ever solved. With a very long scope they might have their place to set the primary but I found by and large they can end up leading me up the garden path.

They dont check secondary alignment and its all too easy to be messing with the secondary to get the beam bang onto the primary spoit and then realise that the secondary has rotated slightly or is no longer square to the focuser.

Very luckily for me both my lasers also broke quite quick so I managed to get a refund.

The only one I liked was the Hotech as it got round most of the problems of slop, miscollimated collimator etc etc even it cant do the secondary set-up but I;d still buy one for field use with a longer scope.

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steppenwolf

steppenwolf

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Laser collimators do work and very well IMHO but you do need to bear in mind my bold text as it cannot be assumed that they will work simply from the box - you do need to think about how use them, ensure that you shim them to make a tight fit in the focus tube and then self collimate them.

Hi Mel, do you prefer daggers or shooting irons? :):(:eek:

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acey

acey

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its all too easy to be messing with the secondary to get the beam bang onto the primary spoit and then realise that the secondary has rotated slightly or is no longer square to the focuser.

If you do the secondary with a laser and the primary with a cheshire, any rotation of the secondary is revealed by the cross hairs of the cheshire not quite lining up with their own reflection. This will lead to a (very) small loss of light at the eyepiece but is otherwise not a problem - star-test will show the scope to be in good collimation.

If a few small tweaks to the secondary lead to it not being square to the focusser then the secondary mount needs replacing.

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TopHouse

TopHouse

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What you can also do with it, is you put the collimater into it and tighten just enough so theat the collimater can be rotated with no play, you rotate the collimater and look down the tube and if it draws circles, the laser is out, i collimated my collimater doing this.

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John

John

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I notice that Antares have introduced a range of barlow lenses with the eyepiece centering facility built into them. They are aimed at imagers but would be useful for a barlowed-laser collimation setup I would have thought.

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johnkirkpatrick

johnkirkpatrick

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Ok I've done my first collimation lol. and boy was it scarry! i took off the primary mirror and cut out a bit of paper the size of mirror and folded it in half then half again then cut of the corner to create a circle in the middle then placed it onto the mirror and used it as a template to stick on a binary folder reinforcer and hoped it was totally center. with my measurements the center was 65mm from all directions. then I moved the secondary mirror into the center of my ep holder using my ep holder cover cap with a 2mm hole in the middle. then moved the secondary till the laser was on the sticky ring, then! moved the primary till the return laser went back to where it came from.

Did I do it properly as its really cloudy here and cant do a star test:(

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johnkirkpatrick

johnkirkpatrick

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Sounds good so far - the best test is the star test though.

I'm surprised you had to put the centre spot / circle on the primary mirror yourself though - most seem to come ready "spotted".

Now that would of been easier if it was, hope all skywatcher scopes do cause thats gona be my next one lol

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