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Orion (A)MN55 Collimation Guidance.

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#1 gdjsky01

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Posted 06 July 2019 - 01:39 AM

Hi All.

I know this has been brought up, but give me a break as I am new to Mak-Newts

very good friend of mine loaned me an Orion 5.5 Mak-Newt (saya AM55 on the back)

I set it on a Celestron Advanced GT mount with quite a few Pounds/Kilos of weight and got it to balance on the mount.

The scope has an amazing Moonlite 2 inch focuser and was at one point returned to Mike Palmeri for service/tuning.

 

However...

 

I let it sit out in 40* weather for a good 30 to 45 minutes.

I then did a star test and the image was horrible. It almost resembled pinched optics. Almost.

 

I put a laser in and the laser missed the center of the mirror (marked by a paper circle) by a good inch or more.

I did not have a hex wrench small enough to move the collimation screws. So I packed it in for the night and used my UC22. ;)

 

So... I did some research here on CN. But it dealt a lot with offset and such. I am gonna assume, and I am not gonna futz with, that the offset is fine. 

 

So please, I have no instructions (but I have the MN180 instructions - Chinese version). Should I proceed as a newt?

I have a super nice LaserMax as well as single beam lasers and barlowed lasers. And sight tubes etc... 

 

There seems to be precious little on mak newts. But my understanding is these AM55s were the bomb optically. And that is why I borrowed it.

 

Thank you for your advice!!!

 



#2 ngc7319_20

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Posted 06 July 2019 - 08:24 AM

 

So please, I have no instructions (but I have the MN180 instructions - Chinese version). Should I proceed as a newt?

I have a super nice LaserMax as well as single beam lasers and barlowed lasers. And sight tubes etc... 

 

Yes, it is nearly the same as a Newt.  The main difference is that the light path needs to be centered on the corrector, whereas it doesn't matter much on a Newt.  So proceed as if it were a Newt and use the Barlowed laser.  Then check the centering of the light path on the corrector. This is where the LaserMax will come in handy -- you can use the grid pattern thing and look at the pattern projected through the scope and onto the ceiling, and see if you are centered on the corrector.

 

If you can't find a solution where everything lines up, it probably means your focuser is tilted, or something like that.  You can put some shims under the focuser, if needed (or maybe it has adjustment screws for tilt).

 

Once you have it all set with the lasers, you can do the final tweak on a real star at high power pointing overhead.



#3 TG

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Posted 06 July 2019 - 10:13 AM

Start with the secondary base as square with the corrector as possible and then proceed as with a Newt. As @ngc7319_20 indicated, the aperture stop in a Mak-Newt is the corrector which has to be square to the optical axis or you will have astigmatism and/or coma. With a Newt , the aperture stop is at the mirror so you can tilt the whole optical axis, including the focuser w.r.t the tube without any ill effects but not so in a M-N. Proper collimation of a M-N relies on it having been built well to begin with.

#4 gdjsky01

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Posted 12 July 2019 - 08:55 PM

Ya know I thought I had it just about tweaked. But one last thing... (or the start of starting over):

Outside focus using a 6mm Baader Ortho I get nice clean centered diffraction rings.

But inside focus the secondary shadow is not quite centered??

 

The images it's putting up are getting to (or are at) snapping to focus (tho a narrow range)

And checking with the LaserMax it seems the secondary is centered.

 

Single Laser is in the primary doughnut, and a barlowed laser the doughnut centered.

Focuser not square??

Ideas?


Edited by gdjsky01, 12 July 2019 - 08:56 PM.


#5 Paul Hyndman

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Posted 12 July 2019 - 09:17 PM

Here ya' go for starters (courtesy of Company 7), THE instruction manual for the Orion® Argonaut™ 6" Maksutov-Newtonian.

 

PS: rotate the laser a full 360 in the focuser and ensure the beam stays centered at the same point on the primary and does not paint an "excursion" pattern on the primary (indicating if the laser itself is properly aligned) or all bets are off.



#6 luxo II

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Posted 13 July 2019 - 08:26 AM

A laser will get it close but there are limits. The final tweaking is best done with a real star.
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#7 Paul Hyndman

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Posted 13 July 2019 - 03:53 PM

A laser will get it close but there are limits. The final tweaking is best done with a real star.

 

Yep. The final tweaks from my MNx6 how-to article:


"A little trick I use to make things easier... When checking with a real star, the importance of having it centered in the FOV was previously stressed (so as to not skew the error). This phenomena  can be used to our advantage, as it actually makes it easier to do a solo collimation. If the defocused image shows a non-concentric pattern (bulls-eye), move the scope so that the star is on the side of the FOV that had the "thin" side of rings, noticing that the error has lessened (If not, try the opposite direction). With the error lessened, tweak the corresponding screws on the primary to move the star back to your center of field. This not only keeps the star in your FOV (making adjustment far easier), but as you re-center the star, the diffraction pattern is being adjusted closer to the ideal. Repeat till perfect."



#8 luxo II

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Posted 13 July 2019 - 11:32 PM

What’s more the Poisson spot should be visible in the centre at high power.

Edited by luxo II, 13 July 2019 - 11:33 PM.


#9 gdjsky01

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Posted 14 July 2019 - 12:08 AM

I do not trust the laser blindly. I was star testing.

What I was asking is

Do any of you know, If the secondary shadow is center outside of focus, but a little off inside of focus, what does that mean?

Maybe I just have to compromise?



#10 TG

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Posted 14 July 2019 - 01:42 PM

Here ya' go for starters (courtesy of Company 7), THE instruction manual for the Orion® Argonaut™ 6" Maksutov-Newtonian.

 

PS: rotate the laser a full 360 in the focuser and ensure the beam stays centered at the same point on the primary and does not paint an "excursion" pattern on the primary (indicating if the laser itself is properly aligned) or all bets are off.

Unfortunately, the collimation procedure in this manual is simply that of a Newtonian. Where the Newtonian differs from the MN is in the initial secondary adjustment for which the manual helpfully says:

 

"If [the secondary isn't centered in the focuser tube], it must be returned to Orion Telescopes to be adjusted, as this cannot be corrected by the user."

 

For the original Argonaut and several subsequent Intes versions, the primary is held to its cell with a central plug preventing the use of autocollimation tools. You can use a sight tube and cheshire, and if you have it a laser, but these are sufficient as long as you start with the secondary centered in the focuser tube *and* its base flat against the corrector, i.e, all collimation screws are evenly tightened. Final tweak is on a star, either real or artificial.




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