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Old 28-09-2020, 11:51 AM
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mental4astro (Alexander)
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mental4astro is offline
 
Join Date: Jun 2008
Location: sydney, australia
Posts: 4,979
Ryan,

When it comes to collimation, the hardest part is just the term "collimation". It only means "aligning the optics".

Too much is made of this process being difficult, and this scares off many people from using Newts. People are not familiar with the term, read about things such as Cheshire eyepiece, auto collimator and then LASERS, and OMG!!! FREAK OUT!!

Collimating tips
There is plenty of info on collimating Newts, and Astro Baby's site is one of the best for newcomers to follow.

There are two things you need to be aware of when it comes to sorting out the mirrors of a Newt:

1, Get the secondary mirror right FIRST!

The secondary is the ugly cousin of the primary and is not recognized by new comers as being just as critical as the primary in the optical train. Not get the secondary sorted first & it doesn't matter what you do with the primary, the alignment of the optics won't work out.

Mess around with the primary first, and you are asking for a world of pain and frustration with the process

2, A laser alone will not do it all!

A laser WILL NOT fix the secondary. A laser is only a tool to help tweak the primary only after the secondary has been sorted out. A laser will not tell you if the secondary is square with the focuser, nor if it is centered with the focuser draw tube, nor if it is sufficiently aligned with the primary. This is the purpose of the Cheshire Eyepiece and the Auto Collimator (collimation cap).

It is possible to "collimate" a Newt with only a laser, but it will be a false collimation, and over time the secondary will be more and more misaligned and the final image will just get worse and worse. This is entirely because the secondary has not been proplerly sorted because a laser cannot determine the unique job/requirements/position of the secondary.

Actually, a laser is not necessary at all! It is only a convenient tool to make the tweaking easier. A Cheshire eyepiece is all that is needed, and star testing to tweak the final part of the primary, which in reality even when using a laser, a star test should be the final verification test that everything is right... but I too am a creature of comfort and I do use a laser, but I also use both a Cheshire eyepiiece and collimation cap to sort out the secondary first.

The terms "primary" & "secondary" are often confused with meaning an order of significance. Truth is that when it comes to aligning Newts, it is the secondary that comes first, not the other way around. And I too made this mistake too when I started out with Newts. I did not understand the role of the secondary in the optical train and I also thought a laser would do it all. I hope this post will help out you and everyone else new to collimating to avoid some of the traps that are not immediately obvious and that astro retailers just cannot know your experience in collimation when you buy a laser from them.

Alex.

Last edited by mental4astro; 29-09-2020 at 08:24 AM.
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