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Both the laser collimator and cheshire eyepiece are tools used in astronomical telescope collimation. What are the main advantages/disadvantages of each? Which one might be best suited to start with for telescope newbies?

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  • $\begingroup$ What is your source? What are you trying to achieve? $\endgroup$ – Carl Witthoft Aug 24 '17 at 13:23
  • $\begingroup$ @CarlWitthoft what do you mean by "my source" I heard collimation lasers need also to be collimated which is tricky and are more expensive and are not always reliable. I just want advice from somebody with experience using both tools to tell its advantages and disadvantages I don't get the downvote $\endgroup$ – PbxMan Aug 24 '17 at 14:17
  • $\begingroup$ By "source" I mean the object which is creating your photons $\endgroup$ – Carl Witthoft Aug 24 '17 at 15:15
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    $\begingroup$ I think it's better to turn to the edit button than the insta-close button when the only problem is the way the question is phrased. This is certainly a good question and was pretty clear from the beginning. Saying "unclear what you're asking" is not the most helpful response here. I'm going to point to the this excellent, accepted answer as supporting evidence that the question was already both clear and excellent and there was absolutely no need of closing it. SE is not Space Invaders and the goal here is not to shoot things down. $\endgroup$ – uhoh Aug 26 '17 at 6:10
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Why not both? (if you can afford them)

Both will do the job, but each has its strengths.

Cheshire eyepiece (or, more properly, Cheshire/sight tube combo, which is the popular combination nowadays):

It's easier to use when the scope is grossly out of alignment. Like, when you put it together for the first time, or after it dropped on the ground and rolled downhill for a minute. But can you do that with a laser? Yes.

It's easier to align the secondary mirror, and it tends to produce dead-on results for this purpose. But can you do that with a laser? Yes.

It is not immune from precision issues. Most parts of the Cheshire are usually well aligned (because they are machined on a lathe), but the crosshairs on the sight tube may or may not be perfectly centered. But can lasers also suffer from alignment problems? Yes.

Recommended Cheshire / sight tubes: the ones made by Catseye.

http://www.catseyecollimation.com/

They make much more than just Cheshire eyepieces, and all their tools are very high quality.

Laser collimator:

It's faster and arguably easier to use for normal daily collimation before you begin your normal observing sessions. But could you use a Cheshire instead? Yes.

A laser is only as good as its own alignment precision. A misaligned laser will not collimate your scope properly. But do Cheshire sight tube combos suffer from precision issues with their crosshairs? Yes.

Recommended laser collimators: the laser collimator and the tuBlug combo made by Howie Glatter. Unfortunately Howie has passed away recently, so either wait until someone picks up where he left off, or find a used laser/tuBlug combo somewhere on eBay or classified ads.

http://www.collimator.com/

Howie's lasers are essentially guaranteed to have zero collimation errors from factory. From anecdotes told by users, these devices tend to keep their perfect collimation even after being dropped to the ground repeatedly.

The tuBlug is not mandatory, but it makes primary mirror alignment much easier.


Keep in mind that you also need a precision center mark on the primary, for these methods to work well. Hopefully it's been placed there precisely from factory; otherwise there are ways to re-center it.


How to verify if the laser is centered:

Place it in the focuser. Do not tighten the screws too much, allow the laser to rotate in the focuser a little bit.

Turn the laser on. Watch where the spot hits the primary. Now rotate the laser in the focuser. If the spot describes a circle as you rotate the laser, then the laser is misaligned.

Different method: Make a V-shaped trough from 2 pieces of wood or aluminum. Placed the through horizontally on a sturdy table. Put the laser on the trough. Turn it on, projecting the spot on a distant flat object, like a wall or fence across the street.

Now rotate the laser in the trough and watch the spot. Does it stay put? Then the laser is fine. Does it move in a circle? Then the laser is misaligned - find the adjustments screws (if it has them) and adjust it until it's perfectly square.

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  • $\begingroup$ Regarding your last sentence, rather than say say the laser is bad, it would be more accurate to say the laser need adjusting, albeit some models are not easily adjustable. $\endgroup$ – Dr Chuck Aug 26 '17 at 9:20
  • $\begingroup$ @DrChuck - you are correct. I've fixed my answer. Thanks! $\endgroup$ – Florin Andrei Aug 28 '17 at 18:49
  • $\begingroup$ I've had a lot of success with the "Barlowed Laser collimation" - e.g. obsessiontelescopes.com/learning_center/collimation/index.php . It uses a laser collimator but rather neatly gets around the problem of the collimation of the laser and/or slop holding it in the focuser. It's very easy if you have a laser collimator, a spare Barlow and if your primary mirror center is marked accurately $\endgroup$ – MartinV Aug 28 '17 at 20:43

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