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How to Collimate your Newtonian

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#401 Starman1

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Posted 09 October 2020 - 05:49 PM

I didn't see this was a Maksutov-Newtonian, so the offset in the secondary is probably already built in.

In that case, the main issue may be simply a matter of rotation of the secondary and touching up the collimation again.

Start with centering the crosshairs on the primary center marker after a bit of rotation.

How you reach in and rotate the secondary, I don't know.  You might have to rotate the meniscus corrector + secondary.



#402 Vic Menard

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Posted 09 October 2020 - 06:02 PM

...the main issue may be simply a matter of rotation of the secondary and touching up the collimation again.

Start with centering the crosshairs on the primary center marker after a bit of rotation.

How you reach in and rotate the secondary, I don't know.  You might have to rotate the meniscus corrector + secondary.

Before the OP jumps on rotation, it would be really helpful if we could see the actual edge of the secondary mirror in the image. It might also be helpful to have an image or two of the focuser relative to the OTA. I've collimated a few MakNewts and I was able to rotate the secondary mirror by loosening the knurled retaining ring that holds the secondary mirror assembly to the meniscus. 



#403 arg2020

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Posted 10 October 2020 - 05:05 AM

Hi Don and Vic, thanks again for taking the time! Since the pictures above I've had the primary cell out again to check the center spot is indeed correctly placed (it is), so everything is completely uncollimated again. See below image with a light shone behind the secondary to highlight the outline.

 

20201010_102258.jpg

 

It seems I have the following options;

(1) Rotation of the secondary via loosening a lock-ring which holds the secondary assembly to the front corrector.

(2) Tilt of the secondary via the three collimation screws.

(3) Longitudinal (down the tube) position of the secondary. I think this is achieved by a centrally located screw between the three knobs controlling tilt. However it doesn't seem to do anything just make the secondary feel loose. (I've been careful not to unscrew it too far and kept the tube horizontal in-case it detaches, apparently this screw is short)

 

I was able to follow the Catseye instructions quite easily and achieve and align the hotspot but I clearly should be doing something before that, I'm just unsure what! I've tried rotating the secondary but that doesn't seem to achieve any symmetry and I'm also not quite sure what I should be lining up. I've read that the distance of the secondary to the front corrector is very important in Mak-Newts and it would seem logical that that should be set first?



#404 Vic Menard

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Posted 10 October 2020 - 07:08 AM

OK--now I can see the edge of the secondary mirror closest to the primary mirror end of the tube assembly (green circle). The blue circle (and cross hairs) are the actual edge of the collimation tool, and the red circle is the primary mirror reflection (still being clipped by the front aperture).

 

You need to pull the combination tool away from the secondary mirror to make the apparent size of the green circle smaller than the blue circle, (it would also be helpful if you could get the cross hair/HotSpot alignment a little closer (using the secondary mirror tilt screws) and then post another image. And I would still like to see an image or two of your focuser so we can determine if it's relatively "square" to the tube assembly (also if it has any leveling screws). It also will be helpful to know the model and specs of your Mak/Newt, and whether you've made any modifications. I'm guessing your collimating tool is a 2-inch AstroSystems LightPipe--long or short?

 

 

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#405 arg2020

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Posted 10 October 2020 - 09:51 AM

Hi Vic, it's a brand new Skywatcher 190MN. The only change I've made is to replace the spot on the primary with a Catseye Hotspot and replaced the collimation screws with Bobs Knobs. The collimation tool we're looking through is a Catseye Telecat XLS.

 

20201010_153500.jpg

 

and the focuser assembly, this hasn't been touched.

 

20201010_152657.jpg

 

20201010_152601.jpg



#406 Starman1

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Posted 10 October 2020 - 10:15 AM

It's one of the LongPerng focusers with a telescoping focuser.

You might try running the focuser out until the focuser's outer drawtube is about half way through its travel, then running the inner drawtube in by the same amount, then pulling the Catseye TeleTube out of the focuser an inch or two.

The purpose of doing this is to have:

--the focuser about midway through its travel, where it has the best alignment with the focuser body.

--the inner drawtube more completely inserted into the outer drawtube, where it has more support and a somewhat better registration

--the Catseye TeleTube well supported but closer to a position where everything can be seen


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#407 Vic Menard

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Posted 10 October 2020 - 01:32 PM

Your secondary mirror needs to be offset (quite a bit) toward the primary mirror (the green circle needs to be moved to the orange circle position). If you don't feel comfortable moving it this far (noting your earlier concern that the center mounting screw will not be long enough), then you should return the scope to the dealer. 

 

Your secondary mirror minor axis is 64mm, I think that puts your required offset at about 5 or 6mm.

 

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#408 arg2020

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Posted 11 October 2020 - 08:11 AM

Hi Vic,

 

I've got the secondary shifting down the tube nicely, but I'm a little unsure what my reference is with regards to how far to go? I'm comfortable moving it and I've shifted it 'a bit', kinda aiming for concentricity with the sight tube wall. I know you said offset by 5-6mm but how would I go about measuring that?

 

In the image below the secondary has been moved down-tube and I've re-collimated using the (what I've just realised is your) CDP protocol. Rather sheepishly, I was just flicking through my copy of New Perspectives on Collimation and realised you in fact authored it 🤦‍♂️ Top stuff!

 

20201011_134837.jpg



#409 phsampaio

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Posted 13 October 2020 - 07:04 PM

Here's mine for evaluation. We were using a cheap shorty Cheshire/combo tool, and the crosshairs were impossible to focus correctly, even by backing away from the tool, so the secondary couldn't be 100% collimated. From what I had before, I think the image quality greatly improved.

As for the primary, I did collimate it correctly after (it's slightly off in the picture), and did a proper a star test later at night and from what I could notice, it seemed preety well collimated.

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#410 phsampaio

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Posted 13 October 2020 - 07:07 PM

Continued:

Here's the secondary under the focuser (still, not 100%)

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#411 Magnius

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Posted 14 October 2020 - 10:48 AM

Question. I've noticed after getting everything collimated well, I've noticed Jupiter and Mars are literally too bright too see anything details at all. I mean like shockingly. 

 

Is this significant increase in perceived brightness normal?

 

Views of starts are crystal clear so I think it's just a function of having never actually looked through the scope properly collimated but wanted to check to make sure there's not something else I should be considering.



#412 Starman1

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Posted 14 October 2020 - 11:27 AM

Jupiter and Mars are very bright right now.

Many are talking about turning the brightness down with a neutral density filter or a planet-specific filter like the Baader Contrast Booster.

If you want to see what that does, try observing through sunglasses to see if the reduced brightness helps you see details.

 

You also have some filters that would help:

23A red--to see dark markings on Mars

21 orange--the same, with light areas also enhanced

12 yellow--for light areas and dust storms.  

56 green--light areas enhanced

82A blue--excellent on Jupiter or Mars' polar cap and limb clouds

Moon filter--might make the brightness less and enable you to see details on the planets.

 

Also, using high powers will help--in the case of your 114mm, 100x or more.

 

You will also see them less bright if you are NOT dark-adapted, so keeping some lights in your observing area helps.

Of course, that makes viewing DSOs impossible, so perhaps you should end your night on the planets rather than observing them in between DSOs.


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#413 Vic Menard

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Posted 14 October 2020 - 01:06 PM

I've got the secondary shifting down the tube nicely, but I'm a little unsure what my reference is with regards to how far to go? I'm comfortable moving it and I've shifted it 'a bit', kinda aiming for concentricity with the sight tube wall. I know you said offset by 5-6mm but how would I go about measuring that?

The green circle is where your secondary mirror is currently positioned. The red circle is the correct placement for  your secondary mirror. If you consider the secondary mirror diameter is 65mm, then the distance you now need to move the secondary mirror is probably about 2mm. The references for optimal secondary mirror placement are the bottom edge of the sight tube and the reflected edge of the primary mirror--when all three are concentric, your secondary mirror placement will be correct. You're almost there...

 

(Edit. Sorry, I should have checked. I meant 64mm.)

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Edited by Vic Menard, 14 October 2020 - 01:07 PM.


#414 Vic Menard

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Posted 14 October 2020 - 01:14 PM

Continued:

Here's the secondary under the focuser (still, not 100%)

Was this taken through a collimation cap or a peep sight? If not, I have no idea how "centered" the camera is above the focuser. Also, you shouldn't cover the primary mirror (you've eliminated the important primary mirror center marker reference). Try again, but this time take the image through the shorty Cheshire--and leave the paper behind the secondary mirror opposite the focuser.


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#415 phsampaio

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Posted 14 October 2020 - 04:45 PM

Was this taken through a collimation cap or a peep sight? If not, I have no idea how "centered" the camera is above the focuser. Also, you shouldn't cover the primary mirror (you've eliminated the important primary mirror center marker reference). Try again, but this time take the image through the shorty Cheshire--and leave the paper behind the secondary mirror opposite the focuser.


Thanks Vic! Yes, it was from a collimation cap. So in theory, it was centered. The first picture was taken from the cheshire.

The second picture was to show the secondary under the focuser, I read in some guides that covering the primary might help in this part.

#416 Vic Menard

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Posted 14 October 2020 - 07:36 PM

Thanks Vic! Yes, it was from a collimation cap. So in theory, it was centered...The second picture was to show the secondary under the focuser, I read in some guides that covering the primary might help in this part.

Well, if you didn't have the primary mirror center marker covered, I could have told you if your focuser axial alignment was OK (the blue cross hairs should be aligned to the primary mirror center marker). And in your Cheshire image, the cross hairs are out of focus.

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#417 Vic Menard

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Posted 14 October 2020 - 07:37 PM

And your Cheshire alignment...

 

 

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#418 phsampaio

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Posted 16 October 2020 - 07:42 AM

Thanks again Vic! 

 

Seems a little off now with the overlay. Next time I' try to adjust the secondary. Thing is, it's very hard to judge on the spot if the blurred crosshair is really centered or not.

 

Regardless, I noticed a big improvement in image quality after aligning the secondary, even if it's not 100%.



#419 FlyingV74

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Posted 16 November 2020 - 09:56 PM

Greetings.  I recently purchased a Zhumell Z8 and I’m still trying to figure out the quality of the collimation that I am applying.  I currently only have the laser collimator that came with the scope.  And I have watched a ton of videos.......,,many of which claim that it is a snap!  But after watching videos of the autocollimator in action, I have a lot of doubts about the quality of the views that some of the folks are getting.  I have also ready many webpages on this subject.  I must say that I am very thankful for all of these great resources. 

 

Tonight I did give the star test a try.  The image was very turbulent.  The circles that I could see looked to be centered and concentric.  But with all of that turbulence in the image, it is hard to say.  

 

Something that I have noticed........when viewing Saturn or Jupiter, when I zoom out the image does not zoom out evenly.  It tends to either spill out on one direction or the planet splits into two.  Is this a sign of a collimation issue?

 

I really want to insure that my collimation is very good.  And I hope to eventually try the autocollimating method, though it might be a bit difficult to do since I usually fly solo.  In the meantime, would buying a good quality collimation cap/Cheshire be a good idea?  I plan on picking up a Barlow lens to give that collimation technique a try.



#420 Waynosworld

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Posted 16 November 2020 - 10:23 PM

 Do you know how a collimation cap works?

 

I made my own out of an old 35mm film container, it was easy to collimate my telescope with it and a laser once I understood how to do it.

 

002.JPG

 

Greetings.  I recently purchased a Zhumell Z8 and I’m still trying to figure out the quality of the collimation that I am applying.  I currently only have the laser collimator that came with the scope.  And I have watched a ton of videos.......,,many of which claim that it is a snap!  But after watching videos of the autocollimator in action, I have a lot of doubts about the quality of the views that some of the folks are getting.  I have also ready many webpages on this subject.  I must say that I am very thankful for all of these great resources. 

 

Tonight I did give the star test a try.  The image was very turbulent.  The circles that I could see looked to be centered and concentric.  But with all of that turbulence in the image, it is hard to say.  

 

Something that I have noticed........when viewing Saturn or Jupiter, when I zoom out the image does not zoom out evenly.  It tends to either spill out on one direction or the planet splits into two.  Is this a sign of a collimation issue?

 

I really want to insure that my collimation is very good.  And I hope to eventually try the autocollimating method, though it might be a bit difficult to do since I usually fly solo.  In the meantime, would buying a good quality collimation cap/Cheshire be a good idea?  I plan on picking up a Barlow lens to give that collimation technique a try.

 


Edited by Waynosworld, 16 November 2020 - 10:29 PM.


#421 Asbytec

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Posted 17 November 2020 - 10:44 PM

Greetings.  

 

I recently purchased a Zhumell Z8 and I’m still trying to figure out the quality of the collimation that I am applying.  I currently only have the laser collimator that came with the scope.  And I have watched a ton of videos.......,,many of which claim that it is a snap! 

 

Tonight I did give the star test a try.  The image was very turbulent.  The circles that I could see looked to be centered and concentric.  But with all of that turbulence in the image, it is hard to say.  

 

Something that I have noticed........when viewing Saturn or Jupiter, when I zoom out the image does not zoom out evenly.  It tends to either spill out on one direction or the planet splits into two.  Is this a sign of a collimation issue?

 

Collimating with a laser can sometimes be problematic. I understand it is best applied to the focuser axis when the thin beam is sufficiently collimated and runs true to the axis of the tool. Reflecting back from the primary mirror may not be the best primary axial collimation which is the most important and highest tolerance alignment for reducing coma. 

 

As I understand the thin beam laser method, if it doesn't strike the primary dead center the laser can reflect off the nearly flat center of the primary at some angle of incidence. This added angle of incidence will cause you to tilt the primary a little more than needed to bring the laser back up the primary axis and into the target. 

 

To align the primary, a Cheshire or collimation cap (as Waynosworld suggests) or a Barlowed laser might serve you better. I made one out of the plastic cover for the focuser. 

 

When you say zoom, do you mean using a zoom eyepiece? If the image is okay in focus at a given zoom, then it's probably not a collimation issue. 


Edited by Asbytec, 17 November 2020 - 10:46 PM.


#422 FlyingV74

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Posted 18 November 2020 - 11:57 AM

Thanks for the replies.

Wayne, I have enjoyed reading your travails with the Starplitter. But unlike many on this forum, I am not envious of you. That thing is a beast!

Unfortunately I don’t have any 35mm films canisters lying around. So I have been trying to figure out how to make a collimation cap from something that I have access to. The other day I picked up a 1-1/2” threaded PVC cap. The threaded area was about 2” in diameter. It fit sloppy in the focuser. So I wrapped it with E tape until it would fit more snug. Painted it flat black. Drilled a small hole in the center and then gave it a try. The fit is still s but sloppy. But I think that it is workable. Tilt it in the focuser didn’t seem to have any effect on what I was seeing through the little hole. Things looked pretty centered and circular to me. But I need to spend some more time with this to know for sure.

Asbytec, thanks for pointing out some things for me to consider. Get the laser exactly centered in the donut when aligning the secondary is likely more critical than I thought. So I will be mindful of that.

Also, I mistyped. I should have said when I focus in or out when viewing a planet, the image blobs out towards one side. At times it even diverges into two blurry planets. I’m just trying to figure out what this tells me in regards to collimation quality.

Finally, the other night I somehow left my laser on and batteries got very low. What I noticed is that with low batteries the laser beam is much more crisp and well defined. So the laser probably needs some tweaks to make it work a little better.

#423 phsampaio

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Posted 30 November 2020 - 12:59 PM

Following posts #409 and #410 (and also #417, Vic's response), I further improved on my collimation.

 

Frustrated with my cheap cheshire/sight tube, I bought a 2" Concenter from TS Optics (along with my new EPs) to help me properly align the secondary. For the primary I used the Collimation cap that came with the telescope.

 

Following are the pictures I took from the collimation cap (the concenter pictures were very bad, as the camera can't properly focus). Still not 100%, but I guess I'm getting there. I haven't had much time this weekend to properly collimate, besides I wanted some feedback on to what's missing and what should the next steps be.

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#424 phsampaio

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Posted 30 November 2020 - 01:01 PM

This is my own annotation. The tilt is still off, as seen by the blue and red circles.

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#425 Vic Menard

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Posted 30 November 2020 - 02:18 PM

OK--here's what I see. Your secondary mirror placement is only slightly off (which may be a slight offset error or a secondary mirror that isn't the "perfect" ellipse for your front end geometry--I'm not sure which, or if it's both)--the green circle is optimal. Your secondary mirror tilt (focuser axis) is about 0.1-inch off (blue cross hairs relative to the primary mirror center marker/donut--the red circle is optimal)--the allowable error for high magnification performance is about 0.4-inch for your 12-inch aperture (about 0.06-inch for a coma corrected 12-inch). If you're not using a coma corrector, I would leave the secondary mirror placement and the secondary mirror tilt "as is". 

 

Your primary mirror axial alignment error (primary mirror center marker/donut centered in the collimation cap) is also about 0.1-inch off (1/2 of the read error)--the allowable error for high magnification performance is about 0.025-inch for your f/4.9 primary mirror--so you need to fix that.

 

For the record--correcting the primary mirror tilt will not change the annulus defined by the red and blue circles (in your annotated image). But the primary mirror tilt is the critical error in your current alignment--if you're not using a coma corrector. If you are using a coma corrector, you may want to tweak the secondary mirror tilt alignment too, but I would start with the primary mirror and check the image performance with an eyepiece--and leave the secondary mirror placement "as is"!

 

 

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