Problems with collimation of my Maksutow-Newton - any advise? - Forums

Topic starter

Sep 16, 2021

Hi out there,

some time ago I bought an Explore Scientific Maksutow-Newton (MN-152 Comet Hunter). The first images were ok and the learning curve was high with all the new equipment I had at that time. I realized, that some of my filters were nearly unusable and fixed this problem by upgrading to something different. Not reached the goal, yet, but I get closer

.

Anyway, the first images seemed to be quite ok for what I was able to achieve. One of the results is my image of the fishhead nebula, where I used really cheap filters (that's where the halos came from)

https://www.astrobin.com/2gtpgw/0/#

Then something went wrong with the scope. I must have done something really bad to it. Suddenly, I had really strong color artefacts around bright stars. The problem can be seen in this image of M101.

https://www.astrobin.com/jcwvqe/

The difference between both photos are the filters (LRGB vs Ha and OIII) but they are not the reason for the problem.

After some research I accidently found a possible solution. I must have dropped the collimation laser at some point and I realized, that it was badly misaligned. If I rotated the laser in the focuser, it does not stay at one position but draws circles on the main mirror. So I adjusted it and thought I had solved the problem. I collimated the scope manually (which I did nearly all the time but with a misaligned laser) and checked the settings with the newly adjusted laser and with the "unsharp star test". It feels like the image quality is a bit better now. It seems, that the artefacts became a bit smaller. The problem is, that I am not sure if I really improved the image quality. Maybe the use of better/other filters reduced the effect and it is now less obvious (especially with narrowband where less light hits the sensor). But the problems are still there. Also, the effects tend to be dependent on the color, because the artefacts have different ones on opposite sides.

I really dont know, what's going on here. I love the scope and the first images were really good. But with those problems, it is unusable.

Can anyone give me some advise, please? What do we see here?

Thank you

CS

Christian

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andrea tasselli

Frequent contributor

Sep 16, 2021

Not sure what is going there or what you have, not seeing the scope in person it is always difficult to judge. But the main points is: do you collimate the scope visually with a star test and if so how does it look (extra-focal and intra-focal). Also how does a bright star looks at high magnification (300x-400x). My take is that you have a tilted corrector (w.r.t. the primary) so it might be a bit complicated to get it fixed as I don't know the mechanics of the scope. Having owned 3 M-Ns and using one currently all I can say is that it doesn't look just a matter of mis-collimation but I'm I hope I'm wrong in this. Send us images of the intra- and extra-focal scope exit pupil and we might be able to help you there.

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Andre Vilhena

Sep 16, 2021

Hello Christian,

I bought the same scope some months and it came with that issue but actually in only half of the image (I used no filters). I sent for repair but instead I got a new one as it seems that is caused by the front lens and it needs specific optical instruments. Over the internet I found someone with the same issue: https://www.cloudynights.com/topic/603592-mn152-comet-hunter-collimation-with-red-and-blue-flares/.

I must add that the replacement one had the focuser train misaligned and it made impossible to properly square the secondary mirror. After that, I quit, returned it and bought an APO. It was a pity because I think that Comet Hunter ticks all the boxes in terms of specs but quality was not that great. And apparently MN design needs to have good quality standards to work fine.

So, apologies for not helping solving that specific issue but I think it's relevant to share my experience with that scope.

Cheers,
André

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Christian Großmann

Topic starter

Sep 16, 2021

Andre Vilhena:
Hello Christian,

I bought the same scope some months and it came with that issue but actually in only half of the image (I used no filters). I sent for repair but instead I got a new one as it seems that is caused by the front lens and it needs specific optical instruments. Over the internet I found someone with the same issue: https://www.cloudynights.com/topic/603592-mn152-comet-hunter-collimation-with-red-and-blue-flares/.

I must add that the replacement one had the focuser train misaligned and it made impossible to properly square the secondary mirror. After that, I quit, returned it and bought an APO. It was a pity because I think that Comet Hunter ticks all the boxes in terms of specs but quality was not that great. And apparently MN design needs to have good quality standards to work fine.

So, apologies for not helping solving that specific issue but I think it's relevant to share my experience with that scope.

Cheers,
André

That is bad news. Thanks for sharing your experiences. I may have to think about the possibilities how to fix it and at the same time try to contact ES. I am not sure, if this will help

Stephan Linhart

Sep 16, 2021 · Edited: Sep 16, 2021

Hi Christian, something else that could cause this is some pinched optics. Maybe mirror/ corrector lens is too tight?

If you rotate your focuser or camera and the artifacts stay in the same orientation relative to the chip, it has something to do with the rotated parts. If they move it is caused by the main optics/ tube.

Good luck in finding the root cause.,

Stephan

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Jan Svagr

Sep 16, 2021 · Edited: Sep 16, 2021

Hi Christian,

unfortunately I had the same issue and it was issue with the meniscus :/ contact your dealer (mine was TS).

regards

Jan

MirachsGhost

Sep 16, 2021

So… Have the same telescope. Had the same problems. I had several calls with Explore Scientific. I sent them star tests. Images down my site tubes. Ultimately, they told me that it was a characteristic of the optics. I hate to be the bearer of bad news. I will say, I love using it visually.

Concise

Andre Vilhena

Sep 16, 2021

Stephan Linhart:
Hi Christian, something else that could cause this is some pinched optics. Maybe mirror/ corrector lens is too tight?

Ich you rotate your focuser or Camera and the artifacts stay in the same orientation relative to the chip, it has something to do with the rotated parts. If they move it is caused by the main price/ tube.

Good luck in finding the root cause.,

Stephan

@Christian Großmann , if I were to fiddle myself I'd follow Stephan's hint. Check two things:

1) The screws that hold the meniscus (the lens) in the outer diameter. They should be slightly tightened but not too much; and evenly tight;

2) When you open the cap in the center of the meniscus, you'll find a large bolt in the center. When tightened, this bolt will press three pins against the meniscus to hold secondary mirror support firm - make sure this bolt is NOT tight during normal operation.

I hope this helps.

André

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Christian Großmann

Topic starter

Sep 16, 2021

Andre Vilhena:
Stephan Linhart:
Hi Christian, something else that could cause this is some pinched optics. Maybe mirror/ corrector lens is too tight?

Ich you rotate your focuser or Camera and the artifacts stay in the same orientation relative to the chip, it has something to do with the rotated parts. If they move it is caused by the main price/ tube.

Good luck in finding the root cause.,

Stephan

@Christian Großmann , if I were to fiddle myself I'd follow Stephan's hint. Check two things:

1) The screws that hold the meniscus (the lens) in the outer diameter. They should be slightly tightened but not too much; and evenly tight;

2) When you open the cap in the center of the meniscus, you'll find a large bolt in the center. When tightened, this bolt will press three pins against the meniscus to hold secondary mirror support firm - make sure this bolt is NOT tight during normal operation.

I hope this helps.

André

Beside the fact that it could be a problem with the optics, your comments are a shimmer of hope. The fact, that it worked well in the beginning is maybe an idicator for the meniscus issue. I am quite sure, that the screws are tight. If I'm correct, I tightened them once after I wondered how loose they are. This is worth a try.

I hope you are right and I can fix it. I will post the results...