Hopefully the Newt collimation questions answered once and for all?

[blusky]

Watch the part that "corrects" the intentional rotational error.

PS A sticky?

[sunshine185]

Brain surgery looks simpler!

[Skybrowser]

Anything about collimation always looks complex to start with. Looks good.

[Karen]

Watch the part that "corrects" the intentional rotational error.

PS A sticky?

Which brings us back to the good ole collimation cap / mirror clip method. There can't be much rotational error if you can see all the primary mirror clips spaced nice and evenly at the edge of the secondary.

[Parus major]

I'm going to be controversial. Dress it how you like but it didn't do very much more than any other video or write up I've seen but got over complicated with toys. If you need such basic direction on collimation you won't feasibly have £120+ of collimation toys on hand.

[Jason D]

I am afraid the person who made that video does not understand the theory of advanced collimation. Laser collimators don't lie as he stated many times. Quality laser collimators, if used properly, will always align the focuser axis with the primary mirror axis. Even when a secondary mirror rotate/tilt error is introduced, axial alignment can be met. The impact of the rotate/tilt error is marginal reduction of the 100% illumination in the FOV. But that impact is minimal and indiscernible for visual observation but might be discernable for astro photography.

Anyway, laser collimators are not the right tool for centering/rounding the secondary mirror under the focuser unless you are using a holographic attachment as shown in the attachmented photos. I use the Glatter laser collimator. Of course, a quality sight-tube can also be used for secondary mirror alignment under the focuser.

[Mr Q]

I think a more important question amateur astronomers should ask is "Does my scope NEED any collimation adjustments?" to begin with.

The answer (before any adjustments are made) is "Do a star test!"

When I got my 10" newt (new), and after splitting several close stars, I wondered the same question - could the scope do better? I was splitting stars down to 3" separation at the time - not bad out of the boxes.

After doing a star test during a hazy, steady summer sky, I tried tweeking the collimation and though only slightly off, my star splitting went down to just above 2" and about 1.5" for a Dawes limit.

No fancy tools - just eye sighting down the focuser tube and a final tweeking during a star test got me to the limits of my scope's designed performance.

So if I can get this kind of performance with an easy, tools free collimation during a simple star test, what's all the hype about? Unless a scope is severly out of collimation, any fine tweeking can be done during a simple star test to bring any scope up to its designed performance.

So the important question is not "How do I do a collimation?" or "What tools do I need to do one?" but should be "Do I need to do a collimation?", and a simple star test can provide the answer.

So save your money for better quality EPs or gas to a darker observing site instead of wasting it on fancy collimating tools that sometimes don't work in the first place due to quality of workmanship.

[Jason D]

How do you adjust your secondary mirror using star collimation? You have stated that a significant improvement was done with star collimation which I do not doubt. Have you tried any of the quality collimation tools? You might be pleased with the additional improvement you might see.

[Macavity]

Right or wrong, in an absolute sense, I do LIKE this bloke's approach to many common problems of setup. With more conventional advice, I began screw twiddling and knob turning FAR too early in the process! LOL. I found that a lot can be achieved by getting line of sight and mechanic adjustment "symmetrical" or as prescribed... I think Web / Video Cams have potential too.

But, having done my best "mechanically", I actually *did* get reasonable agreement with a "laser"... perhaps the "Cheshire" TOO. The "star test" was a bit off though. But then I do feel there can be a "delusion of accuracy" problem with the [iMO] often crude adjustment mechanisms of modestly-priced Newts? But you can significantly improve this latter by filing screw ends, adding a bit o' grease etc. Though my ambitions are less than many? My 8"/F4 Newt is only trying to cover the 8mm (diagonal) of a Watec VIDEO chip. Much of what I do (visually too!) is limited by "seeing"... I sense my eyesight ain't THAT great either.

The Newt is a great (video) "light bucket". If I want to look at Planets or split Double Stars, I'd tend to use my MAKsutov. Slightly imperfect, it may be, but then it STARTS OFF with fairly "text-book", concentric(!) diffraction patterns, both inside and outside focus - And actually retains them fairly well too...

[Catanonia]

If your scope is already "closely" pre colimated, then fine a star test would be great.

But alot of peoples scopes are widely off or they have been taken to pieces for flocking, cleaning or came dis assembled and hence the problem.

Messing with secondaries, primaries at night during limited clear skies is a pain, especially when the work can be done during the day and hence these types of videos are great.

Many people assume their secondary mirrors are ok out of the box and quite alot of the time they are out. Then you are p**ing in the wind with colimation of the primary.

This method on the video is precisely what the Cats Eye method does, but without the expensive auto collimator. Adjust, secondary, primary and back again till bang on.

The one thing I do like about this method is the concentration on the important part, the secondary.

Always remember, work from the focuser - secondary - primary in that order. Ie follow the light path. If the secondary is out, you are stuffed and no amount of messing with the primary will help.

Now as you approach F4 and below, this is VERY important as small errors are greatly magnified.

[Skybrowser]

Dion (who made the video and many more) is a good guy who did say he was about to be controversial in the vid.. I have to say I find this one (and all of his others come to that) to offer a common sense approach to the issues and topics he covers.

I had to watch this one twice though to completely get what he was saying. Got there in the end and will certainly consider all he was saying, especially on secondaries. All of the highly technical talk above doesn't rock many people's boats to be honest (IMHO) and I think the no frills approach he takes are valuable to those of us who want to improve on quality in perhaps a more easily understood way.

[MontyUK]

I have had a Dob 8" for a year and not collimated it yet, partly because star tests show that is appears to be aligned. Does a star test reveal all?

[Jason D]

I think the no frills approach he takes are valuable to those of us who want to improve on quality in perhaps a more easily understood way.

But the video is suggesting using a modified webcam and a laptop with special softwares to center/round the secondary under the focuser -- would you describe that as a no-frills approach? A quality sight-tube could do the same.

As far as the message made in the video several times about “laser collimators do lie” is inappropriate and misleading. After all, many beginners have laser collimators and here is a video with someone who comes across as an authority on collimation is telling them that their laser collimators lie. The appropriate message should have been: You can’t use a laser collimator to center/round the secondary under the focuser. A quality-sight tube is the appropriate tool.

[Jason D]

I have had a Dob 8" for a year and not collimated it yet, partly because star tests show that is appears to be aligned. Does a star test reveal all?

If you are getting nice concentric defocused star rings with a central donut on both sides of the focus at high magnification (>= 300X) then your collimation looks good. Make sure to defocus by a small amount at both sides of focus – enough to show around 6 rings.