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Collimation question

Collimation Beginner
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#1 RodgerDodger008

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Posted 27 October 2021 - 04:43 AM

Hi CNs

Very dumb question really as I know collimation is important.

My scope I started using 6 weeks ago came with no collimation cap, only instructions to use a old film holder cap and punch a hole in it. Who still has film holders, I wish I had haha.

I have not bought a collimation eyepiece yet nor a laser collimator.

What I did do is follow the instructions to check collimation with my eye only, i.e. seeing my eye centered and looking at the position of the primary mirror clips.

I know this is not accurate but it seemed quite close even perfect but obviously I can't say that with this method.

Secondly I viewed stars out of focus with a variety of eyepieces and can see almost perfect circles and in focus sharp dots.

This scope shipped like this and I am wondering do I need to urgently get a collimation eyepiece or is this ok for now?

F6 8inch Dob in my signature is the one I am talking about.

Clear skies! smile.gif


Edited by RodgerDodger008, 27 October 2021 - 05:06 AM.


#2 Medic002

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Posted 27 October 2021 - 06:02 AM

You can view with it without collimation. It will not hurt anything except if it is not collimated well it will just affect the view u see but if it is very close now from what ur seeing visually then it may not be out of collimation very much from shipping. Your star test is what will give u the best information and u say they were almost perfect but not perfect so there is still room for a little improvement. The center ring is what u want to look at when looking at the out of focus star to see if it is out of center or not. The thin outer rings should all be very similar but the larger center ring will be shifted in any direction if it is out of collimation.


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#3 belliott4488

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Posted 27 October 2021 - 06:44 AM

Will you be moving your Dob much? One of the reasons that collimation is such a concern for Newtonians is that by design the primary mirror is held only loosely, to avoid pinching the mirror by tightening the clips too much. This means that if you transport your Newt in a car or jostle it in any other way, the mirror can shift slightly, and you have to collimate it again. 

 

If you're only carrying your scope from indoors to outside, and you can avoid bumping it, it could hold its collimation for a good while. 

 

Once you have the tools, though, it's always good to check the collimation when you first set up. I do it as a regular part of my routine, and it never takes more than a minute.


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#4 Vic Menard

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Posted 27 October 2021 - 07:31 AM

...What I did do is follow the instructions to check collimation with my eye only,..it seemed quite close...
Secondly I viewed stars out of focus with a variety of eyepieces and can see almost perfect circles and in focus sharp dots.

...I am wondering do I need to urgently get a collimation eyepiece or is this ok for now?

If the scope is meeting your expectations, it sounds OK to me. An 8-inch f/6 has pretty relaxed alignment tolerances, and if you're not typically using high magnification (above about 200X), you may not notice any moderate collimation defects.

 

You can order a basic (and inexpensive) collimation cap here: https://agenaastro.c...t-eyepiece.html  It's better than a DIY film holder.


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#5 RodgerDodger008

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Posted 27 October 2021 - 07:45 AM

You can view with it without collimation. It will not hurt anything except if it is not collimated well it will just affect the view u see but if it is very close now from what ur seeing visually then it may not be out of collimation very much from shipping. Your star test is what will give u the best information and u say they were almost perfect but not perfect so there is still room for a little improvement. The center ring is what u want to look at when looking at the out of focus star to see if it is out of center or not. The thin outer rings should all be very similar but the larger center ring will be shifted in any direction if it is out of collimation.

Thanks very much for the advice on looking at the centre ring, will pay attention to that closely next time these clouds clear.



#6 RodgerDodger008

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Posted 27 October 2021 - 07:47 AM

Will you be moving your Dob much? One of the reasons that collimation is such a concern for Newtonians is that by design the primary mirror is held only loosely, to avoid pinching the mirror by tightening the clips too much. This means that if you transport your Newt in a car or jostle it in any other way, the mirror can shift slightly, and you have to collimate it again. 

 

If you're only carrying your scope from indoors to outside, and you can avoid bumping it, it could hold its collimation for a good while. 

 

Once you have the tools, though, it's always good to check the collimation when you first set up. I do it as a regular part of my routine, and it never takes more than a minute.

At the moment it is a short distance from the spare bedroom to the back garden. Saying that I am thinking my next purchase should be either a collimation eyepiece or a laser. 

 

Laser sounds easier tbh but maybe a collimation eyepiece is more reliable? what do you think?



#7 RodgerDodger008

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Posted 27 October 2021 - 07:52 AM

If the scope is meeting your expectations, it sounds OK to me. An 8-inch f/6 has pretty relaxed alignment tolerances, and if you're not typically using high magnification (above about 200X), you may not notice any moderate collimation defects.

 

You can order a basic (and inexpensive) collimation cap here: https://agenaastro.c...t-eyepiece.html  It's better than a DIY film holder.

so far I have gone to 240x with the 10mm eyepiece and Barlow x2.

 

I have briefly "tested' my 7mm plus barlow x2 on jupiter through moderate cloud for about 15minutes. This was Sunday when it got delivered, Wednesday night here now and not stopped raining since.

 

That would 341x the max I will be going to. what should I expect in good seeing if the colimation is out by a significant amount. would I see less contrast and sharpness maybe?

 

also mirror pinching, I wonder can that happen through bad collimation? I dont really understand exactly how a mirror is pinched.



#8 BlueTrane2028

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Posted 27 October 2021 - 08:01 AM

In the attached photo, you can see that the mirror is held to the cell with three clips.

This arrangement, though the implementation is slightly different from one manufacturer to another, is fairly standard among Newtonians.

There's a line between the mirror being too loose and too tight.  If it's too loose it can move around on you and will never be collimated  If it's too tight and the mirror gets pinched, it'll hurt the telescope's performance, often dramatically.

So, if you suspect your mirror is pinched, loosen the clips slightly and try again.

Attached Thumbnails

  • Newtonian Mirror Cell.jpg

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#9 RodgerDodger008

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Posted 27 October 2021 - 08:07 AM

In the attached photo, you can see that the mirror is held to the cell with three clips.

This arrangement, though the implementation is slightly different from one manufacturer to another, is fairly standard among Newtonians.

There's a line between the mirror being too loose and too tight.  If it's too loose it can move around on you and will never be collimated  If it's too tight and the mirror gets pinched, it'll hurt the telescope's performance, often dramatically.

So, if you suspect your mirror is pinched, loosen the clips slightly and try again.

thanks for the pics and explanation, very clear!

 

ok so on the bottom of the primary i have 3 screws that touch the mirror, I know from the instructions these are the ones to adjust when doing colimation. the other three screws hold it in place I think. 

 

so when you saying loosen the clips is it by turning those colimation screws?

 

also if a mirror did get pinched does it damage it or do you just correct the issue by loosening the clips?



#10 BlueTrane2028

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Posted 27 October 2021 - 08:16 AM

The screws on the bottom do not touch the mirror itself, they touch the metal piece that the mirror is attached to.  The pinch would've happened from whoever last installed the mirror into the telescope.  That could have been the factory if it's never been taken apart since, or a past owner/you when need arose for the mirror to be cleaned.


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#11 RodgerDodger008

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Posted 27 October 2021 - 08:54 AM

The screws on the bottom do not touch the mirror itself, they touch the metal piece that the mirror is attached to.  The pinch would've happened from whoever last installed the mirror into the telescope.  That could have been the factory if it's never been taken apart since, or a past owner/you when need arose for the mirror to be cleaned.

ok thanks, yea my views are very good so thankfully no issues like that and not planning on cleaning the primary for a long time so should be good.

 

good to know I can't pinch the mirror by doing colimation wrong.



#12 SteveG

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Posted 27 October 2021 - 12:39 PM

At the moment it is a short distance from the spare bedroom to the back garden. Saying that I am thinking my next purchase should be either a collimation eyepiece or a laser. 

 

Laser sounds easier tbh but maybe a collimation eyepiece is more reliable? what do you think?

 

Only if you purchase a quality laser. The cheap LaserMate non-barlowed lasers are pretty useless if you have a 2” focuser.

 

I recommend a combo tool, which is often called a collimating eyepiece and sometimes Cheshire. It has a 3 tools in one, a site tube for secondary centering, cross hairs for focuser axis, and a Cheshire for your primary. I prefer a collimating cap for the primary, or a true Cheshire (expensive).

 

Here is a good combo tool:

https://www.svbony.c...ating-eyepiece/


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#13 SteveG

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Posted 27 October 2021 - 12:40 PM

Thanks very much for the advice on looking at the centre ring, will pay attention to that closely next time these clouds clear.

One thing not often mentioned, when doing a star test, the star needs to be centered in the fov.


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#14 LDW47

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Posted 27 October 2021 - 12:51 PM

I had 2 SW 8" dobs and a SW 6" dob for years, they were transported by 4x4 and then 14mi by boat, back and forth  Never had a problem with collimation but then again they never got sharply banged around  My collimator sat around gathering dust  Most dobs of 8" or less are known to require very little collimation unless as I say they get banged around not just moved around the way they should be   PS  And the views on a clear, dark nite were awesome, always


Edited by LDW47, 27 October 2021 - 12:54 PM.

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#15 LDW47

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Posted 27 October 2021 - 12:52 PM

Collimating unnecessarily could make it worse, its been known ..........


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#16 Vic Menard

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Posted 27 October 2021 - 01:11 PM

...so far I have gone to 240x with the 10mm eyepiece and Barlow x2.

If you're getting good/sharp planetary views at 240X (detail in Jupiter's equatorial belts (festoons, barges, etc.), or surface detail on Saturn's disk), I wouldn't worry about your collimation. 


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#17 belliott4488

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Posted 27 October 2021 - 03:29 PM

At the moment it is a short distance from the spare bedroom to the back garden. Saying that I am thinking my next purchase should be either a collimation eyepiece or a laser. 

 

Laser sounds easier tbh but maybe a collimation eyepiece is more reliable? what do you think?

I think the laser is more complicated, since you have to make sure the laser itself is collimated*.

 

Since I still have old film cannisters lying around, I made my first collimation cap from one of them, but I soon got one of these: https://www.rigelsys.com/telecoll.html. It's made more accurately than I could, plus it has a nice reflective insert that makes it very easy to use. I use this when I'm adjusting the secondary mirror, although you can use it to collimate the primary as well.

 

Instead of the Rigel Aline cap, I use a combo Cheshire like the one SteveG linked to collimate the primary. I like the convenience of the cross-hairs for getting everything lined up.

 

*EDIT: The main benefit of a laser collimator, I believe, is that it's easier to use on very long Newtonian tubes. For them it might be impossible to reach the adjustment screws while looking through the focuser tube, so it helps to be able to see the guide dot from a slight distance away.


Edited by belliott4488, 27 October 2021 - 03:31 PM.

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#18 Spile

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Posted 27 October 2021 - 04:03 PM

I am more confident about alignment of my secondary and primary with my Celestron Cheshire eyepiece and sight tube combination tool than anything else and that is what I would recommend. I was able to get close with the cap, and yes a film canister did not fit my eyepiece, but the sight tube is easy to use and is my default tool. 


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#19 RodgerDodger008

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Posted 27 October 2021 - 06:35 PM

I had 2 SW 8" dobs and a SW 6" dob for years, they were transported by 4x4 and then 14mi by boat, back and forth  Never had a problem with collimation but then again they never got sharply banged around  My collimator sat around gathering dust  Most dobs of 8" or less are known to require very little collimation unless as I say they get banged around not just moved around the way they should be   PS  And the views on a clear, dark nite were awesome, always

this explains lots as to why mine seems ok. wow sounds like you took those scope to an amazing place!



#20 LDW47

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Posted 27 October 2021 - 06:47 PM

this explains lots as to why mine seems ok. wow sounds like you took those scope to an amazing place!

On the clear nites the skies were Bortle 1 and my SQM-L consistently read 21.9 - 22.05 unless you pointed it directly at the MW

 

ECFB67BA-1EBB-41DB-AD7B-4D998882447A.jpeg

 

2B5D4C5E-5EA7-48A5-804E-4BEBC224861E.jpeg

 

The Big Dipper looking north and the MW looking south out over the Ottawa River  PS  Please bear in mind that the MW has been edired to bring out its full colors but the density of stars is fairly representative when looking through one of my scopes


Edited by LDW47, 27 October 2021 - 06:55 PM.

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#21 BlueTrane2028

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Posted 27 October 2021 - 07:18 PM

RE: lasers and such.  I had a OneSky.  It came with a cheap Cheshire.  I kept it when I sold it and that's all I ever use for collimation.  Can easily get away with just a pinhole cap too.  I don't see the need for a laser.


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#22 JOEinCO

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Posted 28 October 2021 - 03:33 AM

One thing not often mentioned, when doing a star test, the star needs to be centered in the fov.

 

And the other thing is Don't Defocus Too Far.

 

You don't want a giant donut star. Just barely turn the focus knob and you'll see the star turn into one, then two bright rings, with a bright dot in the middle. One or two bright rings is far enough. Then center the dot...it's much more accurate than trying to make a uniform giant donut star.


Edited by JOEinCO, 28 October 2021 - 03:34 AM.

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#23 RodgerDodger008

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Posted 28 October 2021 - 04:47 AM

And the other thing is Don't Defocus Too Far.

 

You don't want a giant donut star. Just barely turn the focus knob and you'll see the star turn into one, then two bright rings, with a bright dot in the middle. One or two bright rings is far enough. Then center the dot...it's much more accurate than trying to make a uniform giant donut star.

thanks you and SteveG gave me excellent advice, i wont try and collimate to a star since it is a manual dob but I will definitely use this method to test collimation.


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#24 JOEinCO

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Posted 28 October 2021 - 07:41 AM

.....i wont try and collimate to a star since it is a manual dob but I will definitely use this method to test collimation.

 

Polaris is your friend. Doesn't move, and it's the perfect brightness for collimating.

 

:::::::::::::::::::::::::::

 

EDIT:  Oooops. I didn't catch your southern hemisphere location. Use a star near the south celestial pole,,,,


Edited by JOEinCO, 28 October 2021 - 09:12 AM.

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#25 RodgerDodger008

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Posted 28 October 2021 - 08:51 AM

Ok I have learnt a few things tonight...

1) I saw what I wanted to see when I thought my scope was kind close to being colimated.

Thanks heaps for all the advice, looking again tonight at stars out of focus I noticed it is out, then I did the eye colomation test again, focused on having my pupil over the target and it visibly out. Not sure how I missed that!

2) I have been spoilt by good seeing since I got this scope. Tonight transparency was great but even though Jupiter was close to the zenith it was like focus was dropping in and out, dont think I have had that before. So this made me look closer at colimation also...

Ok so cheshire is what I am buying asap as in tomorrow.

thanks again!


Edited by RodgerDodger008, 28 October 2021 - 08:53 AM.



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