collimation

Chippy3476 (Danial) · #1 22-12-2013, 03:34 PM

Hi all,
I have a new reflector and am after any advice on collimation. I have no idea what to do. Is it hard and when do I need to do it? I have not got any laser collimator but the instruction manual sais to use a lense cover with a small hole in it??? I am worried that I will mess it up all together if I muck around with it.
Thanks all

glend (Glen) · #2 22-12-2013, 05:37 PM

There are many collimation guides available here and online elsewhere, just look through the Articles forum section or search fo Astrobaby's guide as it also uses a collimation cap approach. Your scope maybe fine but every owner needs to knows how to do it.

barx1963 (Malcolm) · #3 23-12-2013, 12:34 AM

Hi Danial
First thing is not to get tied up in knots about collimation. There are lots of good guides, the one I have used is here
http://www.astro-baby.com/collimatio...on%20guide.htm
Many people get the idea that a scope needs to be perfectly collimated to work, the thing to remember is that it is a case of diminishing returns. If you simply stuck your eye over the empty focuser and checked that you can see the whole primary in the secondary, the scope will produce an image, may not be as perfect or as bright as possible but useable. As you use gear to improve the alignments, the image improves but by smaller steps. Eventually you end up spending hours to get it perfect when there is no discerable difference in the image. You would be much better using that time observing IMHO!
Unfortunately imagers who use newts do need very good collimation, especially if using a fast scope, but for visual use, not so important.
My message is relax, have a go, even if you are not sure it is right, still use the scope, enjoy the views and refine your collimation technique next time.

Cheers

Malcolm

OzStarGazer · #4 23-12-2013, 08:41 AM

I am new too and feel exactly like you. And my manual also says it is possible to use an old film canister (which I don't have) if you don't have a collimation tool. I think I am going to buy a laser collimator anyway, even if I realize it is not necessary. The Seben ones are not very expensive.

glend (Glen) · #5 23-12-2013, 10:42 AM

If you buy a laser collimator make sure that it is able to be collimated itself - some are not. There is a good example of laser collmator adjustment in the Articles forum here. The GSO laser collimators can be adjusted and don't cost a fortune.

barx1963 (Malcolm) · #6 23-12-2013, 11:18 AM

The thing to remember with a laser is there are a couple of potential errors that can occur.
1. The laser itself may not be accurately built or collimated. If the alser beam is not parallel to the axis of the focuser it will never yield accurate results.
2. All a laser can tell you is about the angles of the mirrors relative to each other, especially with solid tube scopes. If you think about it, the laser beam that originates from the focuser could hit the secondary anywhere on its surface and you can tilt both mirrors to give a result that says the scope is collimated. It doesn't ensure that the secondary is aligned underneath the focuser or correctly positioned with the light cone generated by the primary. With a truss style scope it is possible to spot the secondary and use a laser to centre it, but still best to use other methods.

Malcolm

OzStarGazer · #7 23-12-2013, 11:30 AM

Quote:

Originally Posted by glend

If you buy a laser collimator make sure that it is able to be collimated itself - some are not. There is a good example of laser collmator adjustment in the Articles forum here. The GSO laser collimators can be adjusted and don't cost a fortune.

Yes, the Seben laser collimator can be collimated itself.
This is what the description says: The laser collimator can be aligned itself, too. But that is usually not necessary, as it will be delivered well aligned. It uses a common CR2032 3V lithium battery.

MichaelSW (Michael) · #8 23-12-2013, 12:35 PM

Danial,

G'day.

Malcolm has given you some great advice - Don't get tied up in knots about collimation. I wish someone had told me that 4 years ago when I was going crazy reading collimation link after link, suffering information overload, and always feeing the need to try something else.

I was unaware of Malcolm's link to the Astro-baby article on collimation. Just had a read through of the article and in my opinion, it is the best explanation of non-laser collimation process I have seen. VERY USEFUL. And thank-you to Malcolm.

Chippy3476 (Danial) · #9 23-12-2013, 04:20 PM

That is good advice guys. Thanks alot for all your help. When I use a collimation cap I can see the three primary mirror clips reflected in the secondary and the secondary looks centered on the primary mirror. It gives me great views so I am not going to stress myself over collimating until it doesnt look centered anymore. Thanks guys

barx1963 (Malcolm) · #10 23-12-2013, 04:25 PM

Thank you Michael.
I sometimes feel like a broken record with my exhortations to beginners to a) Not let collimation freak you out and b) not let collimation put you off buying a newt/dob.

A little practice and seeing the process at work also helps! Unfornately there is a lot of collimation advice on the net and some is of dubious quality. The other isue is that what is OK for one scope may not be suitable for another. A 130mm f6.9 will be perfectly happy collimated with an old film canister, but my 20" f5 needs at least a cheshire and a confirmation tweak from my Howie Glatter barlowed laser and my 8" f4 works OK with just the Cheshire but if I do a final tweak with the non barlowed laser that seems to give the best result at the EP.

Malcolm

OzStarGazer · #11 23-12-2013, 05:04 PM

By the way mine is collimated too at the moment and I will certainly not touch it until I need to. There is no need to fix what is not broken, but it is good to know what to do/ be prepared when need arises.

PS: The article is very good, I have bookmarked it. Thank you!

Pinwheel (Doug) · #12 26-12-2013, 02:52 PM

Once you start changing things that don't need changing you'll never be happy. Learn the best method for your newt & you stick to it. What size & brand newt do you have? Some one here probably has the same unit & could advise you to the simplest way.

barx1963 (Malcolm) · #13 27-12-2013, 09:28 AM

Quote:

Originally Posted by OzStarGazer

By the way mine is collimated too at the moment and I will certainly not touch it until I need to. There is no need to fix what is not broken, but it is good to know what to do/ be prepared when need arises.

PS: The article is very good, I have bookmarked it. Thank you!

I have a slightly different view. Collimation is something you should feel confident about and the only way to get confident is to touch it! I would actually setup your collimation device, and have a very little play with the setting. Eg, turn one of the primary setting knobs half a turn and see what effect that has. The advantage of doing this is that if you are systematic and careful, you can always reverse the process. But it gives you a good feel for what the various adjustments actually do!

I have done this with all my scopes, gives me a very clear picture of how much I need to tweak things.

In addition I recommend checking and tweaking the collimation on a scope each time it is taken out. Even minor transport will move things around. And the min benefit is that collimation becomes second nature and when the time comes for a major collimation exercise (such as after a mirror clean, a mirror cell rebuild etc) it is a much easier exercise.

Malcolm

OzStarGazer · #14 27-12-2013, 01:04 PM

Well, I have ordered the laser collimator yesterday, although it probably won't be sent until next week....

You are probably right, but I am so afraid to mess it up! But I will try the collimator when it arrives. By the way, I think I read in the description of my scope that it is not necessary to collimate it every time before using it? Although I guess it won't hurt it...

barx1963 (Malcolm) · #15 27-12-2013, 01:34 PM

Quote:

Originally Posted by OzStarGazer

Well, I have ordered the laser collimator yesterday, although it probably won't be sent until next week....

You are probably right, but I am so afraid to mess it up! But I will try the collimator when it arrives. By the way, I think I read in the description of my scope that it is not necessary to collimate it every time before using it? Although I guess it won't hurt it...

Just had a read through previous posts and I have a couple of questions. 1) how do you know it is collimated? Have you checked it yourself or are you relying on what someone else has told you. If relying on someone else eg a dealer, I would strongly urge you to check it. 2) What sort of scope is it? The demands of collimation vary significantly depending on the scope. My old 130mm f6.9 could be quite a way out before the image deteriorated, but in my 20" f5, it really needs to be pretty much spot on. 3) Are you regularly moving the scope? If it is a newt/dob it is pretty much a certainty that things will shift slightly each time it is moved so getting on top of collimation now will be a benefit in the long run.

Malcolm

OzStarGazer · #16 27-12-2013, 02:03 PM

1) Well, I assume it is collimated because it can focus very well. I could see Jupiter's moons even with the 25mm eyepiece, although they were really tiny. Tiny but very clear. Yesterday I could see Orion's belt with the nebula really well too.
In the manual there are also images of collimated vs not collimated when an object is out of focus, and based on those images it appears to be collimated. (The circles of the out-of-focus stars are concentric.)
2) It is a Skywatcher Heritage 130p.
3) I only had it for a couple of weeks and there have been a lot of clouds around, so I only used it a few times. I have only used it on the balcony for the moment. I haven't gone to the beach with it yet.
The laser collimator is on its way, but it is economy from Germany and it hasn't even been sent yet...

Chippy3476 (Danial) · #17 28-12-2013, 01:18 PM

I know mine is perfectly collimated becouse the star test is spot on and everything is centered. I can see all primary mirror clips in secondary and secondary is centered on primary. I only have a small newt a Saxon 114mm 900f/l. In everything I have read it sais that the star test is the most accurate way to test and mine is spot on with the star test. The salesman told me unless I bump it or give it a big knock it will never have to be collimated. I know this is a load of rubbish and I will have to sooner or later collimate but for now im just going to enjoy my scope while it is collimated.

Pinwheel (Doug) · #18 31-12-2013, 05:37 PM

I personally don't trust the laser collimator anymore, I paid heaps for it, trusted it & it was way off. A total piece of crap... Since learning the film canister method & my own learning experiences my scope is now 100%. I hope you didn't buy it from SEBAN (ebay) because thats where my laser crapper came from.

barx1963 (Malcolm) · #19 31-12-2013, 05:51 PM

Yes Doug, cheaper laser collimators are just that, cheap. I have a Howie Glatter one along with the TuBlug and it is magic. Accurate and beautifully machined.
Bit exxy at $368 in total but totally worth it.
The cheap ones in theory can be collimated, but have never heard of anyone successfully doing it. And it will only be worthdoing if the body is accurately made as well.

Malcolm

glend (Glen) · #20 31-12-2013, 09:56 PM

If you read about the technique of using a barlowed laser for collimation you will find a method that is completely accurate every time. There are several lower cost laser collimators that can be accurately calibrated themselves, the GSO being one. I have the GSO laser and it maintains a tight 1Cm spot circle over a target distance of six metres when rotated in the sight device. You don't need to spend heaps to get a good solution. Yes a Cheshire will do the job, as will a eyepiece cap with a hole, but you need to know what your doing and looking at.