Collimation Nightmare!!

[bond19]

I’ve read the website advice, I’ve watched the YouTube videos. Yet I’m still having major problems collimating my OO UK Dob. I’m using a collimating cap & laser collimator. 
 

Is anyone near or around the Blackpool area who can meet and show me hands on how to correctly collimate my scope? I’m losing the plot!!
 

Thanks 😊 

[wookie1965]

If I was closer I would come and show you, depending on the laser collimator you have that may need collimating if it's a cheaper one it more than likely will but you could use the Barlow method. Read these they will help.

http://www.schlatter.org/Dad/Astronomy/collimate.htm

http://www.smartavtweaks.com/RVBL.html

Just take your time once you have the secondary in place you won't have touch that again unless you drop the OTA.

[jetstream]

16 minutes ago, bond19 said:

I’ve read the website advice, I’ve watched the YouTube videos. Yet I’m still having major problems collimating my OO UK Dob. I’m using a collimating cap & laser collimator. 
 

Is anyone near or around the Blackpool area who can meet and show me hands on how to correctly collimate my scope? I’m losing the plot!!
 

Thanks 😊 

What is happening exactly?

[bond19]

I (think) I had the secondary collimated using the colli cap. Then I inserted the laser to align the secondary with the laser dot in the centre of the primaries doughnut. So far all good. Then I collimated the primary using the laser. Again all good. Finally I reinserted the colli cap to check and everything seems massively off 😞

[jetstream]

7 minutes ago, bond19 said:

I (think) I had the secondary collimated using the colli cap. Then I inserted the laser to align the secondary with the laser dot in the centre of the primaries doughnut. So far all good. Then I collimated the primary using the laser. Again all good. Finally I reinserted the colli cap to check and everything seems massively off 😞

Whats it look like to seems massively off?

The easiest,accurate way to collimate is with a cheshire/sight tube combo tool IMHO.

https://www.firstlightoptics.com/other-collimation-tools/astro-essentials-cheshire-collimating-eyepiece.html

 

[jetstream]

If it looks like this its good.

[bond19]

Basically, once collimated using the cap, and then collimated using the laser (and lastly doing a final check with the cap). Suddenly everything looks totally out of alignment?

[wookie1965]

17 minutes ago, bond19 said:

I (think) I had the secondary collimated using the colli cap. Then I inserted the laser to align the secondary with the laser dot in the centre of the primaries doughnut. So far all good. Then I collimated the primary using the laser. Again all good. Finally I reinserted the colli cap to check and everything seems massively off 😞

That will be the laser out do what you did again but this time use the laser Barlow method to do the primary.

[Louis D]

Check for play in the focuser/adapters holding the laser.  I've found if you can wiggle the focus tube and send the laser all over the place, you can't really trust it very much.  Sight tubes and collimation caps are more immune to these vagaries.  The best thing I've found a laser for is getting the secondary pointed more or less at the primary's center after I loosen everything up to start over.  I can see the laser beam hitting the side of the tube or edge of the mirror and make adjustments while looking into the end of the tube in real time.  No having to dodge back and forth to the focuser.  After that, I fine tune with the cross-haired sight tube and collimation cap.  I then double-check with the laser.  Sometimes it's pointing where you expect, other times I have to push the focuser just so to bring it back in alignment.  It could be argued my eyepieces aren't being held in perfect alignment with the optical axis, but their alignment isn't as critical as the mirrors' alignment.

[Les Ewan]

I admit I've never used a collimation laser but I've heard that these devices can themselves be out of collimation. I must say I've always been sceptical about these gadgets after all  amateur observers have been successfully collimating their telescopes for decades before these laser devices came along. Being of the old school I always and always will adjust my optics by eye and with a pinhole cap.

 

[John]

I've never managed to get a laser collimator (I've tried a few ) to agree with my cheshire eyepiece and yet the star test shows the cheshire to be correct. Result - I no longer use a laser collimator.

[johninderby]

Afyer setting up my secondary with a Concentre my Hotec laser gives me spot on collimation results. I no longer use a Cheshire for setting up a secondary.

[John]

2 minutes ago, johninderby said:

Afyer setting up my secondary with a Concentre my Hotec laser gives me spot on collimation results. I no longer use a Cheshire for setting up a secondary.

The Hotech that I had was out of collimation as much as the low cost ones were

I've also tried the Baader and a couple of lower cost laser collimators, all with similar issues. I don't seem to have much luck with laser collimators !

I have actually kept one of the cheap ones because it proved the easiest to collimate itself. I tend to use it more for checking optical alignment of refractors rather than my newtonian though.

 

[fiestazetecmk2]

Hi.My advice would be make sure the laser is collomated. Or it will off every time you insert it in the focuser. Took me a while to collomate my laser.but it's worth spending the time doing it.I used a lathe..and it's perfect.hope this helps.

[jetstream]

10 hours ago, bond19 said:

Basically, once collimated using the cap, and then collimated using the laser (and lastly doing a final check with the cap). Suddenly everything looks totally out of alignment?

Your 12" f4 is going to need some precise collimation, at least my f4 scope does.

I use a sight tube to center the sec under the focuser and then use an accurate laser to line it up on the primary center marker.

Then a cheshire to line up the primary or Glatters TuBlug/laser.

 

[Alan64]

I've no idea as to the type of secondary-hub set-screws that came with your telescope.  In any event, if you can't grab one with two fingers and twist and turn it, then they need to be replaced.  These are the sets-screws, at right, that I replaced with the cap-bolts, at left...

You want them to stick out far enough to grab a hold of them.  You can get those cap-bolts either online or from your local hardware.  The goal is to eliminate a tool between the screws and your fingers whilst adjusting them.

The shorter the focal-ratio of a Newtonian, the more difficult it is to collimate it, and an f/4 is quite difficult, but not impossible.  When working with the secondary, you have to show it who's boss, and with a gloved hand(so as not to get grease and oils on anything). 

Illuminate the tube with a diffused light-source...

Back all three set-screws off and away from the mirror-and-stalk, and with your fingers.  Whilst peering through the peep-hole of a Cheshire, you then grab and orient the secondary-mirror with the other hand until it appears as a nigh-perfect circle, and centred directly under the focusser...

You than finger-tighten the set-screws to keep the mirror in that position.  You do not torque them down at this point.  You want those four "pie slices", as divided by the cross-hairs of the Cheshire, to be of the same size.  Note the use of the orange construction-paper that I used to block the primary-mirror during that exercise.

If the mirror is not centred under the focusser, and perfectly, such is accomplished by the larger screw, usually spring-loaded, there at the centre of the hub...

It moves the mirror back and forth along the length of the telescope.

The secondary-assembly is that one part of the telescope that gives the most fits.  The mirror of same tilts and rotates in most every conceivable direction, but it must come to rest in only one position, and as shown.

Once that's done, you then slightly loosen the secondary set-screws, then simultaneously tilt both mirrors, the primary-mirror with its adjustment-screws, towards one another, carefully and slowly, and until their centres line up...

Note the lovely f/4 off-setting there in the centre, which is normal and occurs automatically during a collimation procedure.  Off-settings are necessary for Newtonians of shorter focal-ratios.  Fortunately, again,  they occur automatically; although some do tweak that, so I've read.

When the cross-hairs of the Cheshire(on the outside), and the mirror-image of the cross-hairs(centre), along with the primary-mirror's centre-spot, all line up together, as shown, you're golden.  It is at that time that you batten down all of the adjustment-screws, of both mirrors, whilst keeping a sharp eye on that scene to ensure that nothing moves out of position when so doing.  Here's the view of that same scene through the collimation-cap...

You then take the telescope outdoors, and see glory, just as I have and do still with my own Newtonians.

But then, for longer tubes, two people may be required to adjust both mirrors simultaneously, one stationed at the front of the telescope, and one at the back.  There is also the option of one person going back and forth, and until the process is completed.  As I understand, laser-collimators allegedly make that aspect easier.  Therefore, if, in the end, and regrettably, you choose to stick with a laser, ensure that the laser is collimated beforehand.

Edited October 29, 2019 by Alan64

[alacant]

17 minutes ago, Alan64 said:

slightly loosen the secondary set-screws, then simultaneously tilt both mirrors

Hi everyone

Not sure about the simultaneous. Get the centre spot of the primary coinciding with the cross hairs of the sight tube by adjusting the secondary only. Then leave it. Now -the nice easy bit- tweak the primary.

But hey, tell me I'm doing it wrong!

Cheers and HTH

**edit: +1 for losing the laser;)

Edited October 29, 2019 by alacant

[JOC]

Have you read the advice here: http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/ That page is the Royalty of how to collimate a reflecting telescope.  If you do everything Astrobaby says to the letter, no matter how daft it sounds you will succeed even I did!

[Alan64]

"The many ways of collimating are as the number of stars in the sky." - Confucius

[Raph-in-the-sky]

10 minutes ago, Alan64 said:

"The many ways of collimating are as the number of stars in the sky." - Confucius

Was that confucius? I though it came from the bible: "take eat this is my body, collimate this is my scope"

[bingevader]

I remember looking at the vids of laser collimators and thinking that they looked simple, quick and easy to use.

I got my cheshire and film canister out and it took me about 10 mins to collimate the 'scope.

I can imagine that if you were travelling far or had a collapsible 'scope that needed collimating at night then a laser collimator might be handy.

[spillage]

I find my baader lazer is great to roughly collimate and they I use a catseye autocollimator for the fine tweeking followed by a star test. I have even managed to tame the 8" quattro.

[jetstream]

One thing- the process can be iterative - sometimes back to the sec after tweaking the primary etc.

[bond19]

Thanks for all the advice everyone. Now I need to take a week off and wade through it all 🤪

[johninderby]

And go lay down in a dark room afterwards. 
 

Baffling at first but will soon make sense. 👍🏻