Bintel laser collimator alignment in focus tube

[nobby2]

I am using a bintel laser collimator in a crayford focuser 2" with 1.25" adapter as supplied in a new 8 inch bintel dob. The problem with colimation is on rotating the collimator inside the focuser you get a wide variation in the position of the dot on the primary e.g the collimator must not be true in focuser or the focuser may not be firm or aligned. I have attempted to tighten all screws and loose parts.

Is this a recognised fault in using this kind of tool Or something in the way i am using it?

[omegacrux]

Yup they do that , mine is the same .
I find there is movement between the laser and the 1.25 adapter , doesn't fit snug enough , I'm going to get a machine shop to make another 1.25 adapt with better tolerance , also the cheaper lasers sometimes the beam is not accurate
Put it in a v block and rotate with it pointed at a wall and see if the beam moves up down

David

[Varangian]

Quite often the laser collimator is not collimated.

http://stargazerslounge.com/topic/87851-how-to-collimate-a-laser-collimator-cheaply/

I steer clear of these but you can get it close enough with them I suppose. I just always felt that it wasn't right and I'm a bit pedantic about collimation (I have flocked my OTA, got some nice eyepieces, clean my primary etc.) so why wouldn't I want my scope as 'collimated' as possible? I sold the laser collimator and bought a cheshire. One of my greatest purchases.

[Steffen]

I find using a laser collimator easier and more precise than a Cheshire. Eyeballing the various elements in the sight tube is difficult and mostly guesswork for me, and my eyes can't get them in focus at the same time. I only use the Cheshire for positioning the secondary and rough initial alignment, after I've taken out the secondary for example. The laser collimator (Glatter + tuBlug in my case) does most of the work, and a star test finishes it off.

The laser collimator needs to be accurately collimated itself, of course, but nothing is easier than checking (and if necessary fixing) that.

A big source of secondary mirror alignment error with laser collimators is non-parallel seat inside the focuser. Howie Glatter makes a nifty gadget called the Parallizer. It replaces your standard 2"-1.25" adapter and makes sure the laser beam is parallel to the focuser axis. This is easily one of the best accessories I've bought in a while, and I use it all the time not just for collimation but with my eyepieces too.

Cheers
Steffen.

[Varangian]

Neil, if you wear glasses or have poor eyesight you may struggle with a cheshire and a laser collimator would be a more appropriate implement. My Dad has been involved in amateur astronomy for 40 years and has used film cannisters to cheshires and now uses a laser due to failing eyesight. He said if he could he would use the cheshire and not the laser. Whenever I am over at his house I take the cheshire and check the collimation of his SDM. My Dad does however use a barlowed laser which he states is far more accurate than an individual laser, and you may want to consider this if you are particularly concerned about accuracy. See the link below FYI. Cheers, John.

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

[Shiraz]

they work really well when set up - see Alexander's excellent how to at: http://www.iceinspace.com.au/forum/showthread.php?t=75601

[Steffen]

That's right, for collimation of the primary mirror definitely go for a barlowed laser (or use a tuBlug), this takes the issue of uncollimated or non-parallel laser beams completely out of the equation.

For secondary mirror collimation you still need a well-collimated and parallel mounted laser, with a precise aperture stop (not a free-form blob that some lasers project). You may also want to check that the primary's centre spot is in fact at the centre. Mine wasn't.

Cheers
Steffen.

[mental4astro]

Ray, ta for the thumbs up on the little write up of mine on collimating lasers. My understanding on the collimation process has grown since writing that article, and it may be time to add to it.

What needs to be also mentioned is lasers DO NOT totally collimate secondary finders. Secondary mirrors also have twist, vertical and lateral factors relative to the focuser that need to be looked at that a laser will not deal with.

Vertical and lateral factors are not as critical, as once the twist factor of the mirror is dealt with, these two other factors will determine just how much light is actually getting to the eyepiece. Optimal vertical and lateral position of the secondary will maximise the amount to light getting to the eyepiece. But give a secondary mirror a nice twist out of alignment (only needs to be a small amount), and you will still get the secondary and primary mirrors to 'collimate', but a simple star test will show you they are not.

Getting my head around this has been the hardest things to learn about the collimation process. The idea of collimation is a simple one: align the blasted optics. At first I too thought a laser was the answer. They are not and ONLY help once the secondary mirror is correctly aligned to the focuser.

There was a fantastic animation created by another IIS member that shows how the case can be that the secondary is not correctly positioned to the focuser, but the laser 'shows' that the optics are 'collimated', but buggered if I can find it now... :rolleyes: But, once the secondary is correctly positioned, a laser can be used to deal with the collimation first of the secondary and then the primary.

Cheshire eyepieces and its variants will deal with this. They are deceptively simple devices, but man, they will brow bash you senseless until you get it. I have only just come to terms with Cheshire eyepieces in the last few months too. There is a protocol to follow with these, and the real tease comes only from learning what to look at in the line of process and what to ignore until the correct sequence number is up for that factor.

Without going into too much detail right now (I've gotta go soon), the sequence in collimation is:

1: Align the secondary to the focuser. This deals with twist, vertical and lateral positioning of the secondary.

2: Collimate the secondary

3: Collimate the primary.

While the GSO, Bintel and other similar laser collimators are not perfect, they do help. For some people that do not want to spend too many $$$ on this hobby, these gizmos are fine. There are more refined units, but don't forget that a simple Cheshire eyepiece will do the same job, AND will deal with your secondary most effectively.

[Jason D]

If you were not referring to one of these two then I am curious to know which animation you were referring to?

Jason

[mental4astro]

:D :thumbsup:

Yep, you beauty mate ! Thank you Jason :)

[Shiraz]

if you want an alternative way to tidy up the secondary angles and offsets - and to get the beam centered as well as possible in the tube - this works well. http://www.iceinspace.com.au/forum/showthread.php?t=82230