Collimation

[kippford]

I received my herritage 130p a few days ago. Last night was the first night that was clear.

Absolute rubbish. I would have been as well looking through a bottle.

My laser collimator arrived today.

When I checked the lock screws on the main mirror they were all completely loose.

I put the laser in and the beam came out of the front almost at the outside edge.

What do I do now?

[mikeyj1]

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

start with that

problem with the laser is that it doesn't sort out the secondary mirror, (at least it can still allow errors in that part of the optical train), so a collimation cap or cheshire would be a good addition for you also..

 

[Dinglem]

Just now, mikeyj1 said:

http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

start with that

 

Beat me to it @mikeyj1 ?

 

[John]

The short version:

Step one: Centre the secondary mirror in the focuser tube.

Step two: Adjust the secondary tilt so that the laser spot is in the centre of the primary mirror - there should be a small "donut" shaped ring in the centre as a target.

Step three: Adjust the tilt of the primary mirror so that the returning beam of the laser strikes the angled target face on the laser collimator in the centre - dissapears down the hole, so to speak.

The above assumes that your laser collimator is itself collimated. That can be tested and if needed, adjusted, before using it like this:

http://www.stark-labs.com/craig/llcc/llcc.html

Astro Baby's guide is well worth a read though as well and goes into a lot more detail on all this than I have.

Final test would be on a star - Polaris is good and Astro Baby's guide shows what to look for.

 

[Timmy]

Hope it's ok to post here, when buying a collimator tool there are massive price variances, will a ebay £15 one be ok for a casual user, or us it worth spending more? 

[mikeyj1]

Just now, Timmy said:

will a ebay £15 one be ok

i have a relatively cheap one, i needed to collimate that first, so it needs to have adjustment screws, but then relatively easy to do, and only needed once (so far).  the better ones, such as Howie Glatter, have a better focus or pattern of the laser which helps also.  Catseye are superb but out of my range.  in summary, cheap one is ok, but you should compliment it with a cheshire (or even just use the cheshire..), although i prefer to have both to hand

[kippford]

1 minute ago, Timmy said:

Hope it's ok to post here, when buying a collimator tool there are massive price variances, will a ebay £15 one be ok for a casual user, or us it worth spending more? 

It was £37 from Rother valley..

 

There are 3 allen screws and a crosspoint screw at the back of the secondary. I have tried to move them, but the single rod holding the whole thing to the scope seems to be in danger of  breaking.

It twists quite a lot. I dont feel comfortable putting so much pressure on it.

[kippford]

43 minutes ago, John said:

The short version:

Step one: Centre the secondary mirror in the focuser tube.

Step two: Adjust the secondary tilt so that the laser spot is in the centre of the primary mirror - there should be a small "donut" shaped ring in the centre as a target.

Step three: Adjust the tilt of the primary mirror so that the returning beam of the laser strikes the angled target face on the laser collimator in the centre - dissapears down the hole, so to speak.

The above assumes that your laser collimator is itself collimated. That can be tested and if needed, adjusted, before using it like this:

http://www.stark-labs.com/craig/llcc/llcc.html

Astro Baby's guide is well worth a read though as well and goes into a lot more detail on all this than I have.

Final test would be on a star - Polaris is good and Astro Baby's guide shows what to look for.

 

I should have added that the dot on the primary is about 2/3 of the way from the centre.

My collimator does a circle of about an inch at 15ft

[kippford]

More junk for the bin then.

[Alan64]

Did you receive the kit new, or used?  The last thing we want is for you to become discouraged and disheartened.  

Hmm, the first thing is to understand the nature of the beast...

This is what a Newtonian, what you have, looks like on the inside, and when the light from an object in the sky travels through it, and to your eyepiece and eye...

It's a clever, albeit wonky, design.  It's also 100% apochromatic, which means that you can observe the brightest objects in the night, Sirius and Venus, and not see the least little bit of false-colour; red, violet and yellow edges and rings around the brighter objects; unnatural colors.

Within that image, the incoming light enters the tube and strikes the larger mirror, the primary, the parabola, at the bottom.  Due to the exotic curve on the surface of that mirror, the light forms a cone, and with a tip.  The goal is to get that tip to the eyepiece and the eye.  The small mirror, the secondary, near the front diverts the tip of that cone at the point seen, and aims it at the eyepiece located at the side of the telescope.  A secondary mirror can move in every conceivable direction, but it must come to rest, locked into place,  in only one position.  Indeed, it is the secondary-mirror and its assembly that gives folks the most fits, as it's the most mechanical portion of the telescope.  

The secondary-mirror is oval in shape...

...however it's tilted at a 45° angle, and as a result it appears as near to a perfect circle, as you see it through the focusser tube, and also as the primary-mirror "sees" it...

You need a collimation-cap... https://www.firstlightoptics.com/other-collimation-tools/rigel-aline-collimation-cap.html 

With it, you can see the entire optical system inside...

That's what your own should look like, if it's well collimated.  Here's another collimation guide...

https://garyseronik.com/a-beginners-guide-to-collimation/

We'll be looking forward to your success.

[Ricochet]

13 hours ago, kippford said:

There are 3 allen screws and a crosspoint screw at the back of the secondary. I have tried to move them, but the single rod holding the whole thing to the scope seems to be in danger of  breaking.

It twists quite a lot. I dont feel comfortable putting so much pressure on it.

I would suggest that you hold the central section of the mirror holder to prevent any stresses being passed on to the secondary stalk. It is also important that you understand how the screws work. The central screw pulls the secondary up to the correct height and the outer three push against it to lock it at the correct angle and orientation. Your first move should be to turn the central screw anticlockwise a touch as this single movement will drop the mirror down a fraction and release all the tension in the system. 

However, before you do this I would check that you are fully extending the telescope. If one of the trusses isn't fully extended then this will tilt the whole system in a manner consistent with where your laser is hitting the primary mirror.

13 hours ago, kippford said:

My collimator does a circle of about an inch at 15ft

How about in the telescope? Is the variance significant compared to the size of the dot? If you have a 2x barlow then you can use the barlowed laser method for primary collimation and the inaccuracy of the laser won't matter.

[kippford]

Thanks for all the help.

I thought I was doing all the things mentioned.

I had a look at it today. I discovered that the whole secondary assembly had rotated a bit round the axis of the rod.( I should have checked that but assumed it would be tight)

I was able to twist it back by hand, it seems fairly firm.

The laser dot was right in the middle but I had to move the primary screws quite a bit to get the beam to go through the hole.

I tested it on a house across the valley and it seems ok.

Now I will have to wait for clear skies.

Thanks again.

 

Colin.

[Moonshane]

Don't forget that it will need about 5 minutes per inch of aperture (25-30 mins) outside before you will get good high power views. You can observe at lower power immediately though if you want to do so. 

[kippford]

I have spoken to a few people about this and they say they would never have been able to correct this.

Is it normal to get a telescope in such a bad state?

[Moonshane]

I think you need to speak to someone used to collimating newtonian telescopes. You could (and I often have) strip it down to component parts and rebuild it with no issues so adjusting the collimation is eminently possible. 

Keep calm and try my guide

 

[kippford]

Yes but I have no experience and people I have spoken to said they would not have been able to correct this. They would have bought a product they could not use.

[Moonshane]

Have you read any of the guides ? Or is there a club nearby you could ask for help?

[Ricochet]

10 hours ago, kippford said:

Is it normal to get a telescope in such a bad state?

No, they are usually pretty close to spot on. Had you gone back to your supplier (assuming is a proper astro shop) I suspect they would probably have taken it back and sorted the collimation for you. 

[Moonshane]

I don't disagree with Ricochet but collimation is a simple process and is something any newtonian scope owner needs to learn to ensure they get the best from their scope.Once the secondary is aligned, the primary is the only thing that needs doing each time and this takes literally about 10 seconds with such a short scope as you can move the primary whilst viewing the effect on the collimator. I'd personally never recommend a laser collimator and suggest you return it if possible and swap for a Cheshire collimator like this one https://www.firstlightoptics.com/other-collimation-tools/astro-essentials-cheshire-collimating-eyepiece.html

Unlike laser collimators a Cheshire based tool can be used for all aspects of collimation, including centering the secondary in the draw tube. I think in your case, the collimator is not accurately aligned and this is also an issue not affecting the above linked tool.

 

[Carbon Brush]

A few years back I was browsing in Rother Valley Optics.
A customer came in to ask about his scope, a 130 newt I think. Basically he was not getting the views he thought he ought to be getting.
The scope was drop shipped from the importer - as is often the case.

Ian (the shop owner) asked a few questions about eyepieces, what night, etc, and came to the conclusion that collimation probably needed looking at.
He recommended the customer bring in the scope and he would sort it.

The customer asked about how long it would be and the reply was while you wait.
Then he asked how to learn about collimation and was told it would be a lesson/demonstration session.
Not a vanish into the back and return with an aligned scope.

An excellent example of how a proper astro retailer can look after you.

Collimation is quickly learned.
Even a scope that was not correctly built (holes drilled in the wrong place, etc) can have the errors identified and corrected.
Even a complete strip down, as mentioned by Moonshane, is not a big issue. Newtonians are generally very simple.

Hope this helps, David.
 

[Alan64]

It is quite easy to break down a telescope.  But it is a good practice to document the process with photographs, and notes perhaps, to reference when reassembling, and just as I did when I disassembled my 150mm f/5 Newtonian...

Now, many of those images within that also detailed numerous enhancements and improvements that I undertook.

"Up there" is so very far away, save the Moon, as it's easily seen, although it is still small.  Only a telescope will reveal other, more, than the bright and dim dots and patches seen with the naked eye.  This is all there is within a Newtonian...

...consisting of the focusser, the two mirrors within their retaining hardware; and all off and out of the tube.  Here is the most mechanical aspect of a Newtonian: the secondary-mirror and its assembly, assembled, and disassembled...

...very few parts actually.  There are two ways of mounting a secondary mirror(and its base to which it's attached): by the hub and its spider-vanes seen there, but also via a rod or stalk, and like your own...

That mirror is positioned there as the focusser and the primary-mirror would "see" it, but it's oval in shape as well.

That secondary-assembly is from my 114mm f/8...

A Cheshire or collimation-cap would make it much easier to collimate.  This is actually how you would view the scene of your own, with its stalk instead of the spider-vanes as I had shown previously; although no difference really, at all...

It's all there within that image...

1. The primary-mirror, all of the white area seen; you can see its three retaining-clips, too.

2. The secondary-mirror, actually its shadow, black, there in the centre, and in the centre of that, the reflective underside of the collimation-cap(or Cheshire), and in the centre of that, the centre-spot of the primary-mirror, and in the centre of that the very small hole of the cap or Cheshire, and through which that image was taken with a camera.

Dare I suggest that you might toss that laser into the bin, or at least set it aside?  I've always viewed them as gimmicky, certainly the inexpensive units.

[kippford]

I have ordered a cheshire collimator, but if I had not had the laser I would have had no idea why I could not see through the telescope.

[Charic]

Don't bin that laser?

http://www.micosmos.com/enlaces/collimation_with_a_Barlowed_Laser.pdf

I've been through all the issues with said lasers and although I  now find that the Cheshire tool is more accurate for my needs ( long version Cheshire rather than the shorty.) I still maintain the use of my laser, but I generally only Barlow the laser when away from the house, which is more accurate for my needs, as I'm not able to look down the focuser and reach the collimating screws at the same time, so the Barlowed  method is more practical plus the laser beam does not need to be that accurate, just on!

[kippford]

I got home a couple of hours ago to a clear sky. No time to cool down a telescope, so I went out with binoculars and saw the orion nebula for the first time in my life.

It was just a smudge, but a smudge I have been longing to see.

It may be cloudy here most of the time but when it clears up it is amazing.

I am so glad I moved here away from all the light pollution.

 

[JOC]

There was no-one more scared of loosening screws on a reflector than I was.  In the finish and armed with a £15 2nd hand Cheshire I followed Astrobay's to letter i.e. did absolutely everything no matter how odd it sounded and it all went wonderfully.  FWIW although I don't recommend following any other set of instructions or video - Astrobaby has it licked - watching a few youtube videos will give you the confidence that even the floppiest of mirrors with the loosest screws can be recovered and its worth watching a couple just for that lesson, don't try and do what they do, follow astrobaby instead, but seeing all the screws loose and then tight again is quite educational.