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My SkyWatcher 190 MN - Maksutov - Newtonian

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#1 sonny486

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Posted 14 October 2020 - 10:58 AM

My journey with this telescope began about 3 years ago.  I purchased this telescope from Woodland Hills Camera and Telescope.

 

I thought I knew everything I needed to know about collimation and alignment of a Mak-Newt.

 

I immediately purchased a Moonlite focuser, the 2” (CR) version.  I lined it up with the factory center spot on the secondary mirror and I thought it would be great.

 

After replacing the focuser the scope exhibited oblong stars.  At one point, I thought the scope had astigmatism due to a bad mirror figure or such.

I removed the rear cell and removed the small cork squares in the mirror support structure and put in my own cork to support the primary mirror.  I removed the old center spot in the primary mirror, and put in my own (catseye center spot).

Put everything back together and still had the same issues.

 

I checked everything I could but still always had issues with improper illumination and star shape issues.

The scope sat in the corner gathering dust while I used my 140mm Refractor.

 

A read many posts here on Cloudy nights and found some great info on offset secondary mirror installation. 

Spent some time taking the whole scope apart and found the factory center spot on the secondary mirror was not in the proper place at all! 

I removed the factory spot with alcohol and began by looking at the support shaft of the mirror.

 

I looked at the secondary mirror arrangement and found the easiest way to mark the center spot was to look down the support shaft of the secondary mirror and put the center spot right in the middle of that.  

I marked the side centers of the mirror with a white board pen and then eyeballed the center mark with a permanent ink sharpie. (You can remove the mark with alcohol if needed)

 

The next major thing I did was change from the moonlite 2” CR to the Moonlite 2.5” CRL focuser.  I wanted the bigger focuser because I had an APS-C and Full Frame cameras.  I used a laser collimator to align the new focuser.  The new focuser could rotate a complete 360 degrees. 

 

This really helped me align my focuser by allowing me to rotate the focuser and observe the laser spot on the primary mirror.  I adjusted the bearings so the laser would not move at all while rotating the focuser.  This ensured my focuser had no angle at all. 

I placed a cheshire in the focuser and began working on moving the secondary mirror in and out of the tube to align the mark I made on the secondary mirror.  It was off quite a bit.  I made sure the secondary mirror mark was in the center of the cheshire cross hairs.  Then I put the laser back in the focuser and aligned the secondary mirror, then aligned the primary mirror.

Checked it again with the CatsEye Autocollimator and alignment looked great.

 

I took some shots last night and had fantastic images.

 

Conclusion: The SkyWatcher 190MN is a fantastic telescope, HOWEVER; the stock focuser is not good for astrophotography so you will need to be prepared for a lot of work to get alignment right after replacing the focuser. 

 

I recommend using the larger focuser (Moonlite 2.5 CRL) because it does allow you to completely eliminate and angle errors from the focuser to the secondary mirror.

 

Do not rely on the center spot mark on the secondary mirror unless you verify it is marked properly.  My center spot was in the center of the mirror, not on the mirror support shaft.

 

 

 

https://www.cloudyni...watcher-190-mn/

 

 


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#2 glend

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Posted 14 October 2020 - 03:42 PM

You are a victim of the classic mistake that MN190 owners made that ruined their scopes. The MN190 had a secondary mounted on the rear of the corrector glass, and the offset is set at the factory and should never be touched. Sadly, some people decided to do a focuser upgrade and acted like this was a standard newt, and changed the offset. The scope was then, as we say down under, " buggered".  

Moonlight was happily selling focuser upgrades until it was brought to their attention, by me, that the MN190 adaptor they provided did not allow the focuser to be mounted forward on the tube to where the focuser tube could be properly centred over the secondary (which was spotted just for that alignment by the factory). Once I brought this to Moonlight's attention, and provided drawing to indicate how the adaptor base should be machined to allow it to move forward, the secondary offset could be preserved (provided you never moved it in the first place).

I had the original Moonlight prototype adaptor in my MN190 for years, and never touched the secondary offset.

Some MN190s were sold on by owners that had tried to adjust the secondary, sadly these scopes may still be floating around the market, and should be avoided.

The MN190 is a wonderful scope, but the golden rule is never try to change the secondary offset.


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#3 rlillard

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Posted 17 October 2020 - 01:48 AM

Would you share that drawing and the date you observed Moonlight's redesigned focuser being shipped?  I have been looking for a MN-190 in the used market and want to be able to distinguish "buggered" from "unbuggered".

 

...and a followup question:  What is the effect (damage) one would experience in a photographic image when using a buggered ( a technical term) MN190 ?


Edited by rlillard, 17 October 2020 - 01:58 AM.


#4 sonny486

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Posted 19 October 2020 - 11:31 AM

Would you share that drawing and the date you observed Moonlight's redesigned focuser being shipped?  I have been looking for a MN-190 in the used market and want to be able to distinguish "buggered" from "unbuggered".

 

...and a followup question:  What is the effect (damage) one would experience in a photographic image when using a buggered ( a technical term) MN190 ?

What I noticed the stars bright center would be offset.  In extreme cases the scope looked like it had extreme coma over the entire image.  

 

When I figured out the secondary mirror center, and 'fixed' it, the stars had the brightest part is in the center of the airy disc.  

 

This is probably the best scope I have, now that it's fixed.  I really enjoy it.

 

In response to the focuser, I wish the scope came with a quality focuser to match the quality optics.  However the cheap focuser forces people to replace it, and sometimes the focuser screw holes do not match the center of the factory mirror.  That's when you would need to check everything.

 

In my case, it seemed the center spot was placed on the mirror as a center for the mirror, if your mirror is not placed on the support shaft properly, it won't be correct.  Taking the time to make sure you have the mirror center spot right down the center of the support shaft, then making sure that spot is right in the middle of the focuser drawtube (I used a cheshire for that) Than you can align the scope properly and get fantastic images!

 

I use this scope almost every session because of it's fast speed f5.3 @ a 1000mm focal length.  



#5 John Miele

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Posted 19 October 2020 - 03:23 PM

Same here! Now that I finally fixed my collimation (caused by replacing the focuser and not understanding the importance of the SM position just as glend described) I LOVE this scope! It has replaced my TS130 apo triplet as my primary imaging scope. It hits the sweet spot for my ASI1600mm in terms of image scale and focal length and gives great star images all across the field. Except for being a tad on the heavy side, I cannot fault it. 

 

P.S. I just drove my MN190 250 miles to a dark site and when I chucked it up on the mount and checked the collimation it was still dead on. And when I drove it back home and mounted it back in my yard, the primary was still dead on and the SM required the barest turn of a screw to touch it up.


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#6 sonny486

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Posted 19 October 2020 - 03:45 PM

Same here! Now that I finally fixed my collimation (caused by replacing the focuser and not understanding the importance of the SM position just as glend described) I LOVE this scope! It has replaced my TS130 apo triplet as my primary imaging scope. It hits the sweet spot for my ASI1600mm in terms of image scale and focal length and gives great star images all across the field. Except for being a tad on the heavy side, I cannot fault it. 

 

P.S. I just drove my MN190 250 miles to a dark site and when I chucked it up on the mount and checked the collimation it was still dead on. And when I drove it back home and mounted it back in my yard, the primary was still dead on and the SM required the barest turn of a screw to touch it up.

Yes, it does hold it's collimation well.  I think it is a great scope, if you can make sure the secondary is where it needs to be.



#7 AstroBruce

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Posted 19 October 2020 - 05:23 PM

Yes, it does hold it's collimation well.  I think it is a great scope, if you can make sure the secondary is where it needs to be.

The secondary is where it needs to be when it comes from the factory. Don't bugger it up by moving it! It is already properly offset away from the focuser and down the tube. The only adjustment, other than standard collimation, is to slide the focuser up or down the tube to align the optical axis with the mechanical axis. This is necessary to align the primary with the meniscus.

 

Bruce



#8 JayS_CT

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Posted 25 November 2020 - 09:20 AM

You are a victim of the classic mistake that MN190 owners made that ruined their scopes. The MN190 had a secondary mounted on the rear of the corrector glass, and the offset is set at the factory and should never be touched. Sadly, some people decided to do a focuser upgrade and acted like this was a standard newt, and changed the offset. The scope was then, as we say down under, " buggered".  

Moonlight was happily selling focuser upgrades until it was brought to their attention, by me, that the MN190 adaptor they provided did not allow the focuser to be mounted forward on the tube to where the focuser tube could be properly centred over the secondary (which was spotted just for that alignment by the factory). Once I brought this to Moonlight's attention, and provided drawing to indicate how the adaptor base should be machined to allow it to move forward, the secondary offset could be preserved (provided you never moved it in the first place).

I had the original Moonlight prototype adaptor in my MN190 for years, and never touched the secondary offset.

Some MN190s were sold on by owners that had tried to adjust the secondary, sadly these scopes may still be floating around the market, and should be avoided.

The MN190 is a wonderful scope, but the golden rule is never try to change the secondary offset.

A very timely post...  I have the SW MN190 and was considering a Focuser upgrade.  I assume (since you worked so diligently with Ron at Moonlight), that the MN 190 focuser they have now is properly machined?  Thanks again!

Jay S.



#9 glend

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Posted 25 November 2020 - 03:33 PM

Actually the original drawing went to Moonlight during consulting in the focuser adaptor design, I will see if I still have a copy. I can assure you that the current Moonlight adaptor plate for the MN190 is as per the original drawing. I do have some photos of the prototype and I will try to find them to post here. In the mean time, the base adaptor must have slightly slotted holes that allow the focuser to be properly positioned directly over the secondary ('in its original factory set position). 



#10 glend

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Posted 25 November 2020 - 04:02 PM

Ok I have found my original thread on the Moonlight focuser upgrade with the custom adaptor plate.  The link is here:

 

http://www.iceinspac...t=MN190 focuser

 

It was originally published on the Southern Hemisphere IIS forum. Photos are part of the thread.



#11 JayS_CT

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Posted 28 November 2020 - 10:32 AM

Ok I have found my original thread on the Moonlight focuser upgrade with the custom adaptor plate.  The link is here:

 

http://www.iceinspac...t=MN190 focuser

 

It was originally published on the Southern Hemisphere IIS forum. Photos are part of the thread.

Thanks!  :-)



#12 Eric Seavey

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Posted 05 December 2020 - 03:17 PM

I just came across this thread, and I replaced the original focuser with a feathertouch.  I too messed up my collimation beyond belief.  I did figure out how to get the collimation correct, and basically what it comes down to is having the meniscus and primary mirror parallel to each other.  Depending on the position of the eyepiece (and the focuser) you will need to make sure that the distance of the secondary mirror to the meniscus is such that the image circle is in the centered in the eyepiece.  In order to do that, you determine how far the secondary mirror needs to be from the meniscus, which you must do with the secondary mirror flush against the meniscus.  In order to have the secondary mirror flush against the meniscus, you need to temporarily remove the tension spring in the secondary mirror.  Once the secondary mirror is flush against the meniscus, you need to make sure the secondary mirror is not turned.  Using good quality collimated laser collimator in the eye piece, you will see that the laser will not be cast the red dot in the center of the primary mirror.  First, turn the secondary such that the laser dot is centered in the horizontal direction.  Second, measure accurately how far the laser dot needs to move in the vertical direction to be centered.  Let's say you measured 2.4 mm, then the secondary mirror needs to be also moved 2.4mm away from the meniscus. All this required disassembling your scope, and I even removed the primary mirror to attach a paper ruler along the primary mirror to determine the offset of the secondary mirror.  Now I have fantastic collimation with beautiful round stars. 



#13 JayS_CT

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Posted 05 December 2020 - 06:59 PM

Ok I have found my original thread on the Moonlight focuser upgrade with the custom adaptor plate.  The link is here:

 

http://www.iceinspac...t=MN190 focuser

 

It was originally published on the Southern Hemisphere IIS forum. Photos are part of the thread.

Hi Glen,

So I read the other article and have spoken with Ron about getting what I need to upgrade the focuser on my MN190.  I already have the focuser body and spacers..  I'm planning on adding the High Res. Stepper Motor on mine as well.  Ron indicated this will compromise the fine focuser a bit because of the slip clutch assembly, but not enough to make it unworkable.

I did want to find out about your use of the 1" spacer vs. the 1/2" spacer they recommend.  Understand the impact to back focus.  Like you, I want to be able to add a filter wheel as well.  So just to be clear, it sounds like all I need to be able to do is slide the focuser and center on the secondary?  I have a Chesire eyepiece to do that job.  What was the large "orange" circle in one of the pics you had in the other thread after disassembly?

Appreciate any other thoughts you may have....

Jay S.
 



#14 sonny486

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Posted 17 July 2021 - 12:34 PM

Here is how I now align my SW190MN - 

 

https://drive.google...iew?usp=sharing



#15 Eric Seavey

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Posted 30 July 2021 - 05:13 PM

The key to properly collimating a MakNewt, is to have the primary mirror and meniscus parallel to each other.  This requires the offset of the secondary mirror from the meniscus to be correct.  Many people who replace the focuser end up with the secondary with a wrong offset, and that is what needs to be adjusted.  Also, it is easy to accidentally turn the secondary mirror while adjusting the collimation screws. It is important to make sure the rotation of the secondary is correct.

 

Enjoy my Little Cocoon Nebula (SH2-82) I imaged a the beginning of this month with my MN190.

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#16 sonny486

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Posted 31 July 2021 - 02:29 AM

Built a Carbon Fiber MN190.

Custom MN190 Carbon Fiber
Album: Custom MN190
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