Collimation guide

[Baz6170]

I highly recommend this guide to collimation, it takes away a lot of the mystery about aligning your scope, and just works. I collimated my Revelation 8" dob in about 15 minutes following this guide, and that was the first time I'd ever done it.

http://www.garyseronik.com/?q=node/169

Hope it helps!

Baz

[FunkyKoval35]

Hmm.. I am not an expert, but there is something wrong with this guide... It is not possible to perform correct collimation, especially for imaging, without correct eyepiece holder position and centering secondary mirror holder(spider) - and that was not mentioned in this guide at all.

[NGC 1502]

Hmm.. I am not an expert, but there is something wrong with this guide... It is not possible to perform correct collimation, especially for imaging, without correct eyepiece holder position and centering secondary mirror holder(spider) - and that was not mentioned in this guide at all.

Hope you don't mind me saying, but are you reading the same link ? http://www.garyseronik.com/?q=node/169

Step # 2, about 2/3 of the way down the link, says how to align the secondary. Easy to miss with a quick read.

Regards, Ed.

[Captain Harlock]

That's the link I used as well a couple of months ago, and, as a complete beginner, found it easier to understand than any other guides on collimation I found online.

[lensman57]

I highly recommend this guide to collimation, it takes away a lot of the mystery about aligning your scope, and just works. I collimated my Revelation 8" dob in about 15 minutes following this guide, and that was the first time I'd ever done it.

http://www.garyseronik.com/?q=node/169

Hope it helps!

Baz

This is a very good and simple tutorial for collimating a newtonian for observing or basic imaging for most beginners. I am afraid that if you are an owner of a fast scope with imaging in mind this level of collimation will not do. IMHO the makers of the telescopes could help quite a bit by providing reference points for the center of the focuser ( to aid orthogonality ) and even the secondary to aid collimaton the same way that nowadays the center of most primaries are marked to aid collimation. I have seen experinced users reorting to use of expensive tools and software to get the light distribution right, these could easily be avoided by just having 3 reference points.

Regards,

A.G

[Baz6170]

This is a very good and simple tutorial for collimating a newtonian for observing or basic imaging for most beginners. I am afraid that if you are an owner of a fast scope with imaging in mind this level of collimation will not do. IMHO the makers of the telescopes could help quite a bit by providing reference points for the center of the focuser ( to aid orthogonality ) and even the secondary to aid collimaton the same way that nowadays the center of most primaries are marked to aid collimation. I have seen experinced users reorting to use of expensive tools and software to get the light distribution right, these could easily be avoided by just having 3 reference points.

Regards,

A.G

You make a good point A.G; however, I posted the link in this section specifically for beginners who I (maybe wrongly) presumed would just be setting up a scope for observing rather than imaging.  I completely appreciate that for imaging, this guide is probably too simple, but for observing I have yet to find another guide that takes the mystery out of collimation and explains how to achieve it without going into tonnes of theory and pages of text, something which could quite easily put beginners off owning/using a reflector.

[jetstream]

Hmm.. I am not an expert, but there is something wrong with this guide... It is not possible to perform correct collimation, especially for imaging, without correct eyepiece holder position and centering secondary mirror holder(spider) - and that was not mentioned in this guide at all.

Seroniks guide is good and there are many levels of collimation. He doesn't mention an autocollimator either, but this tool is what is really needed for imaging collimation. His guide will give people a nice start in the collimation process.

If anybody wants a bit of fun, try an AC

[kirkster501]

That's an interesting article in that he recommends twiddling with the primary collimation bolts FIRST to get the collimation cap hole centred in the primary as a first task.  I have always got the secondary centred first and then fiddled with the primary..

[lensman57]

That's an interesting article in that he recommends twiddling with the primary collimation bolts FIRST to get the collimation cap hole centred in the primary as a first task.  I have always got the secondary centred first and then fiddled with the primary..

I think that this makes sense as  it will take the issue of the orthigonality of the focuser tube to the optical axis out of the equation. If the primary is centered  to the focuser first then all other adjustments will be correct to this reference, this way if the focuser is not dead orthonal it does not matter.

A.G

[Astrosurf]

This is a very good and simple tutorial for collimating a newtonian for observing or basic imaging for most beginners. I am afraid that if you are an owner of a fast scope with imaging in mind this level of collimation will not do. IMHO the makers of the telescopes could help quite a bit by providing reference points for the center of the focuser ( to aid orthogonality ) and even the secondary to aid collimaton the same way that nowadays the center of most primaries are marked to aid collimation. I have seen experinced users reorting to use of expensive tools and software to get the light distribution right, these could easily be avoided by just having 3 reference points.

Regards,

A.G

Can you provide a link to a good guide for imagers? I'm never happy with my collimation. It confuses me! That's why I've always used simple guides like this thread's one.

[lensman57]

still

Can you provide a link to a good guide for imagers? I'm never happy with my collimation. It confuses me! That's why I've always used simple guides like this thread's one.

Hi Alex,

It took me six months to get my Quattro 8s to a stage that is suitable for imaging but just. There is still a small degree of error in the rotation of the secondary, about 2~3 degrees, and some small issues with centering but in the interest of sanity i have called it quits. I think so long as you get round stars that look like a star then you should leave it alone. I think that the crude focusers fitted to these scopes causes more problems than critical collimation . I have a 150 PDS that suffers from this and one day I have to take the focuser apart and sort it out.

I followed Astro Baby's guide initially and then this video is worth a watch.http://www.youtube.com/watch?v=8ROvNH5uwDo.

Regards,

A.G

[Astrosurf]

Many thanks A.G.

[Jason D]

Personally, I do not recommend Gary's guide -- the one referenced in this thread.

Gary stated: "So what are we trying to do when we collimate our scopes? Just this: ensure that the eyepiece is aimed at the center of the primary mirror, and that the primary is aimed at the centre of the eyepiece. That’s it. End of story."

According to Gary, centering/rounding the secondary mirror under the focuser for optimal illumination is not part of collimation.

Gary stated:  "How do you spot overly complicated collimation advice? Here’s one fool-proof way. If step #1 is “square the focuser,” you’re in for a rough ride — guaranteed." then later he stated "The first thing you’ll want to do is square the focuser. Just kidding!"

Gary is belittling guides that start off with ensuring the focuser is squared yet his diagrams suggests a setup that starts with a squared focuser and even centered/rounded secondary mirror. Basically he is saying not to worry about the hassle of squaring focusers and centering/rounding secondary mirrors because you can safely assume these are always done when you start collimation. Look carefully at all his diagrams. There isn't a single diagram that shows a non-centered/non-rounded secondary mirror.

If you compare the diagram titled "In this illustration, neither the primary mirror or secondary is correctly positioned" and the one titled "After Step #1 is completed." you can see how the primary mirror reflection shifted. This is inaccurate. There is nothing you can do with primary mirror adjustments that will end up shifting its reflection within the secondary. All you are doing is changing the tilt of the primary mirror -- you are not shifted.

In step#2 section, Gary stated "Because even if you have collimated your scope so that the eyepiece is aimed at the centre of your primary mirror and the primary is aimed at the centre of the eyepiece (which you did by performing step #1)," This is grossly inaccurate. When you align the primary mirror center spot reflection with the collimation cap pupil reflection, you are ONLY guranteeing that the primary mirror is aimed at the eyepiece but not the other way around. In fact, in his diagram of step#1 it is clear that the eyepiece is NOT aimed at the primary center.

Then Gary continues by stating "you still want to make sure that the secondary mirror is feeding 100% of the primary mirror’s light to the eyepiece". Now he is saying that centering the secondary mirror under the focuser is an important collimation step. But initially he said collimation is only about aiming the eyepiece at the primary and vise versa. What is confusing is that the secondary mirror in his diagrams is already centered/rounded yet he walks the reader through the steps of placing a paper behind the mirror to align it.

I found the next paragraph to be ironic because he made remarks at the start of his article about the complexity introduced by other guides that start with squaring the focuser yet he himself present us with an even more complex procedure: "Use a tape measure or ruler to measure the distance from the top of the tube to the centre of the focuser. The distance from the top of the tube to the centre of the secondary mirror should be the same. The easiest way to judge the centre of the secondary is to mark that point on back of its holder with a pencil, that way you don’t have to worry about touching the mirror itself".

After step#2, he kept the primary mirror spot reflection aligned with the collimation cap pupil reflection. This is inaccurate. When you adjust the secodary mirror, the reflection of the optical axis will no longer intercept the focuser axis at the collimation cap. Try it.

He describes step#3 as a repeat of step#1. This is inefficient. Step#1 is useless since step#2 will undo step#1. So, basically his guide comes down to step#2 then step#3. Step#1 should have been centering/rounding the secondary mirror under the focuser but he skipped this step.

In the last section, he stated "If instead you aim your eyepiece slightly away from the centre of the focal plane, the image will be blurred somewhat by a nasty optical aberration called coma." The wording of this statement is inaccurate. If should have been stated as "if instead you MOVE your eyepiece slightly away from ......etc". Aiming the eyepiece away from the center will NOT introduce coma but rather a focal plane tilt between the eyepiece and the primary mirror.

Another inaccurate statement "In fact, strictly speaking, the secondary doesn’t really influence collimation — its positioning only affects the illumination of the focal plane." But Gary stated that aiming the eyepiece at the primary center is part of collimation and the only way to do it is by adjusting the secondary mirror.

Gary is confused about the secondary mirror alignment. There are two distinct secondary mirror alignments:

1- Centering/rounding the secondary mirror under the focuser. The main objective of this alignment is to optimize field illumination by centering the 100% illumination area in the FOV.

2- Fine adjust the secondary mirror to align the center spot with the cross-hairs of the sight-tube (or to direct the laser to the primary center). The main objective of this alignment is to eliminate the focal tilt between the eyepiece and primary mirror focal planes.

3- The 3rd alignment is the primary mirror alignment which involves aligning the center spot reflection with the cheshire (or redirecting the laser beam reflection back to its source). The main objective of this alignment is to eliminate coma by ensuring both the focal point of the primary mirror falls along the focuser axis.

In summary, collimation consists of 3 alignments.

Jason