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How bad is my collimation?


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Hi all. 

I'm really struggling with collimation. I've read multiple guides and watched videos but I just cant seem to get it right.

Pic attached is as good as I've managed. I know it's not perfect but is this at least usable? I've gone out with it and everything is a little fuzzy so I guess not? Unless I'm just imagining it?

Any tips would be much appreciated :)

Screenshot_20201122-235459_Gallery.jpg

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It doesn't look too bad in my humble opinion, a wee bit off in the centre, but I don't get too fussy if the stars will focus down to decent points of light. They can look like fuzzy, almost boiling blobs if the seeing conditions (not transparency) are poor. For example, nights when the stars really twinkle - that's actually a sign the jetstream is overhead or the atmosphere is unsteady. Also the mirror might not be cooled down or there are heat thermals rising off a roof or area you are viewing over, etc. Just thinking of other things that might affect this. 

I can see one of the primary holders in the bottom of the pic but not the other two, most guides call for all three showing equally, but I recall reading somewhere about secondary mirror offset and that some reflector telescopes may never have all three clamps showing in the Cheshire. But I am not 100% sure on that!

I'm a 'lazy collimator' and just use a cheap, non-barlowed laser to make sure the secondary is properly aligned so that the laser hits the centre of the primary mirror's white circle, then collimate the primary with the three screws on the bottom to get the laser into the bullseye on the collimator tool.

I then sometimes check it with a Cheshire, but don't think it was ever out enough to bother me. I'm a nebula and galaxy observer, no photography, so not too fixated on tight star points, but I do want things reasonably sharp. I tell a bit of a lie, I did stack some photos from an f4 dob which requires good collimation, and the stars were nice and tight on those, so can't be too far off to notice visually!

I'm sure others will weigh in here on this, it's a common topic that has a lot of different answers and opinions!

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6 minutes ago, HutchStar said:

Having read a few more guides I think my primary mirror is off?

Do you have someone to help you? If so, look through the Cheshire while someone gently turns one primary screw at a time until the crosshairs are centred on the circle. If it starts to go the wrong way, have them immediately stop of course and pull it back the right direction. You can do this yourself by making a small adjustment, then checking the Cheshire and so on, but it takes a lot longer than having someone do the fine tuning to the primary. If I'm talking cobblers here anyone, please let me know! Once you've set it, it becomes a lot faster to do in the future should you need to.

Edited by Ships and Stars
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2 minutes ago, Ships and Stars said:

It doesn't look too bad in my humble opinion, a wee bit off in the centre, but I don't get too fussy if the stars will focus down to decent points of light. They can look like fuzzy, almost boiling blobs if the seeing conditions (not transparency) are poor. For example, nights when the stars really twinkle - that's actually a sign the jetstream is overhead or the atmosphere is unsteady. Also the mirror might not be cooled down or there are heat thermals rising off a roof or area you are viewing over, etc. Just thinking of other things that might affect this. 

I can see one of the primary holders in the bottom of the pic but not the other two, most guides call for all three showing equally, but I recall reading somewhere about secondary mirror offset and that some reflector telescopes may never have all three clamps showing in the Cheshire. But I am not 100% sure on that!

I'm a 'lazy collimator' and just use a cheap, non-barlowed laser to make sure the secondary is properly aligned so that the laser hits the centre of the primary mirror's white circle, then collimate the primary with the three screws on the bottom to get the laser into the bullseye on the collimator tool.

I then sometimes check it with a Cheshire, but don't think it was ever out enough to bother me. I'm a nebula and galaxy observer, no photography, so not too fixated on tight star points, but I do want things reasonably sharp. I tell a bit of a lie, I did stack some photos from an f4 dob which requires good collimation, and the stars were nice and tight on those, so can't be too far off to notice visually!

I'm sure others will weigh in here on this, it's a common topic that has a lot of different answers and opinions!

Thanks very much! It did cross my mind that the fuzziness was down to the atmosphere (or my scope still cooling) but I just couldn't shake the paranoia that I'd completely screwed up the collimation.

 

I've got a laser collimater coming this week which I hope will help.

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Just now, HutchStar said:

Thanks very much! It did cross my mind that the fuzziness was down to the atmosphere (or my scope still cooling) but I just couldn't shake the paranoia that I'd completely screwed up the collimation.

 

I've got a laser collimater coming this week which I hope will help.

I really like the laser - it's a doddle and going by the Cheshire, it works very well! Have fun!

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Both your primary and secondary look off to me. Firstly concentrate on centering the secondary before tackling the primary. a laser collimator will not help with the secondary, i use a camera live view and mire de collimation over the top to help centre the secondary.

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4 hours ago, barkingsteve said:

Both your primary and secondary look off to me. Firstly concentrate on centering the secondary before tackling the primary. a laser collimator will not help with the secondary, i use a camera live view and mire de collimation over the top to help centre the secondary.

Ok thanks. I'll have another go tonight and see how I get on.

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Collimation is just something that you can spend ages getting right, don't rush it.  If you find it difficult to center the secondary, carefully place some paper between the primary and secondary so you are only dealing with one mirror.  Then it's a matter of centering the circle of the secondary in the circle of the circle of the focuser draw tube.

Then remove the paper and adjust the primary so that you then get the edge of the primary centred in the focuser, and the reflection  of the primary in the secondary centred.  It doesn't have to be exact, but it needs to be closer than what you have it.  A laser such as Hotech or a cheshire (there are DIY option for a Cheshire) eyepiece will help.  You also don't need to do this at nighttime. 

Good luck

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That looks pretty good.

Try a star test. Point the scope at the pole star. Use a high power. Now see if you get circles either side of focus and a nice small star when in focus. If you do then your good. Also enjoy the blue pole star companion!

Mark

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In my opinion its better, but you are still not there yet.

Ignore the spider web on the mirror, I was in the process of cleaning the scope, and was documenting collimation before i removed the mirrors.  This is what you are trying to achieve (this is on a 200P Explorer, your scope might look a little different).  It wasn't great getting the image, and the camera was slightly off centre, but you can see how everything forms nice circles within a circle

If you then centre a bright star in the eyepiece or camera, and rack the focus all the way in both directions you should see concentric circles form

 

P1019092.JPG

airy rings.png

Edited by malc-c
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1 hour ago, malc-c said:

In my opinion its better, but you are still not there yet.

Ignore the spider web on the mirror, I was in the process of cleaning the scope, and was documenting collimation before i removed the mirrors.  This is what you are trying to achieve (this is on a 200P Explorer, your scope might look a little different).  It wasn't great getting the image, and the camera was slightly off centre, but you can see how everything forms nice circles within a circle

If you then centre a bright star in the eyepiece or camera, and rack the focus all the way in both directions you should see concentric circles form

 

P1019092.JPG

airy rings.png

Thank you, I appreciate the pictures. I'll use them as a comparison in future.

 

Took the scope out tonight and its significantly better than it was. Still not perfect but I can get a clear focus again which is nice. Was able to find M81 and M82 for the first time which has really made my night.

All in all I feel like I'm just about getting the hang of this now. Will try to get the collimation even better tomorrow. 👍

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A few years ago I had an issue with my 200P, and there was several members positive that the issue (additional diffraction spikes) was down to poor collimation.) was down to poor collimation  The thread ran for almost a year, and in that time I must have stripped the mirrors out, reassembled them and collomated the optics fifty times.  In the end it was proven that the issue was a manufacturing defect in how the stock secondary was coated, and the close tolerances in the focal path that was the cause not poor collimation, but all that collimation practice was good to learn.  Not to say that I'm an expert, there are guys on here with scopes that require fine tuning and the collimation has to be within a really tight margin of error, and are thus far more experienced in the subject than I am.

What telescope have you got?

Where abouts in the world are you?

It maybe that someone is local to you and could pop along with a collimator and set you up, and thus teach you the process. 

Edited by malc-c
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On 26/11/2020 at 01:30, malc-c said:

A few years ago I had an issue with my 200P, and there was several members positive that the issue (additional diffraction spikes) was down to poor collimation.) was down to poor collimation  The thread ran for almost a year, and in that time I must have stripped the mirrors out, reassembled them and collomated the optics fifty times.  In the end it was proven that the issue was a manufacturing defect in how the stock secondary was coated, and the close tolerances in the focal path that was the cause not poor collimation, but all that collimation practice was good to learn.  Not to say that I'm an expert, there are guys on here with scopes that require fine tuning and the collimation has to be within a really tight margin of error, and are thus far more experienced in the subject than I am.

What telescope have you got?

Where abouts in the world are you?

It maybe that someone is local to you and could pop along with a collimator and set you up, and thus teach you the process. 

It's a skywatcher 200p. 

I'm in the South West. Was thinking I'll probably look at joining a club once lockdowns are over. In the meantime I'm just relying on online guides and this forum for all my questions.

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Regretfully you are not local to me, so I can't help.

If I can locate that old thread and pick out any tips on collimation and post them here...  With Newts collimation is all part and parcel with ownership.  In reality, you don't need to do it often, and it will be set within tolerance from the factory.  It's only if you take the scope apart that it can be a daunting task.

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Here's a link to the post that detailed the issue I had, with all the attempts to collimate the scope.  Like I said, my issue turned out to be with the coating on my secondary, but there is a lot of information on overcoming collimation issues in the thread.  Sit down with a beer or a cuppa and have a read - might help

https://stargazerslounge.com/topic/159748-200p-colimation-or-poor-optics/

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