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Ross1204

What collimation tool. Laser or Cheshire?

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Hi,

I have recently purchased a Skywatcher 200pds and before using it for the first time I would like to check it's collimation.

I have already done some extensive research on the subject which has ultimately lead me to astrobaby's collimation guide (great guide). I'm just wanting some final advice though on which tools are best for a beginner?

A collimation cap and Cheshire?

Or

Self centering adapter and laser collimator?

I unfortunately don't have the budget to get a howie glatter or cats eye setup but I'm sure I can at least be in the ball park with the two stated above.

Thanks 

Ross

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The first thing you should do before trying to collimate it is to take the telescope outside, let it cool and then do a star test. Only then, if the star test shows eccentric rings, not concentric, should the telescope be collimated.

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If it ain't broke don't fix it, carry out a star test first to see if it needs collimating. In all probability you will need more collimate it sometime in the future, i find an old 35mm film container with a small plastic mirror (superdrug loyalty card) stuck on the inside to be the best tool I've got, far better than my wandering red light In a tube that cost a fortune

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Having had a real adventure with my first collimation sortie I ended up with both a laser and a Cheshire.  In the finish I succeeded with the Cheshire and Astro Baby's collimation guide (you've already found it - follow it to the letter with a Cheshire and all will become clear as you proceed).  I didn't need the laser, but in the finish it was most satisfying to stick it in the system get a perfect bounce back through everything to confirm that I'd really succeeded!

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I have both, but  the Cheshire is the one I use/trust all the time.

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29 minutes ago, Ceramus said:

I have both, but  the Cheshire is the one I use/trust all the time.

So do I, and I use both.  In particular, I find that the (Hotech) laser is a great way to check things in the dark, and give a final tweak, before imaging.  Otherwise, it's mucking about with an eyepiece, or altering the camera settings, and finding a star to do a star test.

It's certainly essential to understand something of the whys and wherefores of collimation with basic (and effective) tools before trusting to a laser.

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I use the following method: 

Set the secondary with a Cheshire/sight tube

Set the primary with a barlowed laser 

Check the alignment of the primary with a Cheshire or collimation cap

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Collimation  cap or cheshire to centre and "round" the secondary mirror under the focuser. Even with a  self centering adapter fitted directly into the focuser tube I find a laser is too sensitive to slop. Then a barlowed laser or cheshire crosshairs the collimate the primary.

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Hello,

I would like to thank everyone for their extremely helpful advice with regards to which collimation tools are best.

I think the best step forward would be to try and understand how to complete a star test and check how the mirror alignment is right now. I currently only own the standard eye piece which came the scope so would imagine I have to look in to purchasing something with more magnification to perform the test. After checking I shall look in to getting a collimation cap and Cheshire to start with then when the budget allows I shall look in to getting a barlow and laser.

Ross

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The eyepiece with the lowest number, if that's say a 10mm will be ok.

The test is straight forward. focus on a bright Star, then de-focus one way or the other. Your looking to see the pattern that forms, a series of concentric circles/rings. They just need to be central/centered............follow the guide.

Of all the tools, Cap, laser, Cheshire, 35mm film cap or  eye alone?  I prefer the accuracy of the Cheshire tool. I own a 'long version'  which for me aids in the accuracy in aligning the secondary mirror. I like all methods, prefer the Cheshire, and Barlow the laser for a quick check when away from home, out in the field.

If you had available all the methods, you could use either of them with a good degree of accuracy, even the laser ( it too needs collimation) but you will settle for just one overall. 
Did I say I preferred the Cheshire!

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Your SW200 will have a collimation cap already. Lasers are good PROVIDING that they too are collimated, and to do that you need to make a collimation rig (check youtube) and test it on a wall or similar, and the further away the better. I bought a Segen one, a cheapy in comparison to others, and it was badly collimated. Therethen followed hours of fiddling to get it to a point of some accuracy. I ended up getting the FLO premium cheshire (twice the price of the laser!) and find this the best. 

I use the laser to get the secondary right, and the cheshire for the secondary. 

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It's worth noting that if you do a star test the star has to be in the centre of the field of view. An off centre star defocuses in the same way as one in a scope that needs to be collimated. 

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Absolutely, and to prevent the Star from moving across your field of view, Polaris is pretty stable for this type of test. 

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27 minutes ago, Daz69 said:

I use the laser to get the secondary right, and the cheshire for the secondary. 

I think you meant:

"I use the laser to get the PRIMARY right, and the cheshire for the secondary. "

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Just now, AKB said:

I think you meant:

"I use the laser to get the PRIMARY right, and the cheshire for the secondary. "

That might explain why i cannot see anything through my telescope :D:D:D 

Yes, that's what I meant lol.

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On 4/3/2017 at 20:50, Charic said:

The eyepiece with the lowest number, if that's say a 10mm will be ok.

The test is straight forward. focus on a bright Star, then de-focus one way or the other. Your looking to see the pattern that forms, a series of concentric circles/rings. They just need to be central/centered............follow the guide.

Of all the tools, Cap, laser, Cheshire, 35mm film cap or  eye alone?  I prefer the accuracy of the Cheshire tool. I own a 'long version'  which for me aids in the accuracy in aligning the secondary mirror. I like all methods, prefer the Cheshire, and Barlow the laser for a quick check when away from home, out in the field.

If you had available all the methods, you could use either of them with a good degree of accuracy, even the laser ( it too needs collimation) but you will settle for just one overall. 
Did I say I preferred the Cheshire!

I currently own one eyepiece which came with the scope and don't think that's suitable so what would you or anyone suggest/recommend for star testing? 

The scope has a focal length of 1000mm and aperture of 200mm

Ross

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I've always understood that you want to star-test with an eyepiece of the same number as that of the telescope's focal-ratio.  The telescope's focal-ratio is f/5, therefore a 5mm eyepiece.  In addition, it is said that the same eyepiece is also the highest power possible, whilst maintaining a sharp image(200x), but under better seeing conditions you can certainly go higher, especially on the Moon, if of interest.

You could choose a 6mm just as well, or 2x-barlow a 10mm or 12mm for same.

 

Edited by Alan64

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Alan64's method is sound and spot on. Its also the theory I would adopt, matching the eyepiece to the size of the focal ratio of the telescope, not only for a star test, but a simple way of choosing an eyepiece for high magnification. For me thats a 6mm eyepiece.
The 6 mm can be exceeded, but using a 6mm for me provides me with 200x power ( matching the size of the aperture in mm, as a guide to my realistic magnification / power ) when conditions allow. The 12mm comes next and about 30mm for my eyes ( f/6  = 6 x size of pupils ) though you will see I actually use a 32mm. Everything else is a luxury.

Try the eyepiece that you have (?) but the higher the power the better.

 

  

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On 03/04/2017 at 21:05, Ricochet said:

It's worth noting that if you do a star test the star has to be in the centre of the field of view. An off centre star defocuses in the same way as one in a scope that needs to be collimated. 

This is a very good point, and one that seems to be rarely mentioned in discussions.  Wondering why this might be, since it's so fundamental?  An eyepiece with cross-hairs helps establish centre, of course!

 

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Best to learn with a collimation-cap and/or Cheshire Sighting-Tube. Then you can get a laser if you wish. But learning about what you're doing is why the Cheshire and colli-cap win my approval.

Dave

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12 hours ago, Dave In Vermont said:

But learning about what you're doing

I agree with this, I learned a huge amount about how things on my telescope worked when I completed my first collimation a few weeks ago.

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I'm in agreement with Dave on this one - I actually a think a collimation cap on it's own is fine for visual in an f5 Newt. It provides enough to tell:

1) Can you see the primary centred under the focuser (i.e. in the middle of the hole in the cap, a couple of mm either was is fine) and is it nice and round?

2) Can you see all three mirror clips and they all about the same distance out from the centre (if they are a bit out, leave it, you're more likely to do harm than good - this only needs adjusting if something is significantly out)?

3) Is the reflection of the hole in the collimation cap bang on the centre of the hole in the primary mirror centre spot? This is the only one that needs adjusted with any regularity.

If you've got all that your scope is collimated and good to go.

Billy.

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All budget lasers require collimation themselves.  Unless you're 100% certain that the laser is well collimated, you're wasting your time.  Stick with a colli cap and a sight tube. Collimation is so simple and straightforward once you grasp what you are actually seeing when you look down the focuser.  Just my opinion of course. 

Ally

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I bought the cheapy Saben too... Yep, way off collimation. However I did get a certain pleasure building this contraption to collimate the collimator. Now I just need to collimate the collimator collimator.

 

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