total impossibility to collimate an MN190

[FABIAN MARIN]

For 1 year now that I am trying to collimate my MN190, with different optical elements, and finally I bought a self-adjusting laser, which continues to give me serious problems, there is surely someone in the forum who can give me that special information, that nobody has yet been able to provide , I swear I will try everything but I think I am getting worse, more and more, and I do not achieve anything, just frustration, this particular telescope has a mark on its secondary mirror that I try to place in the center with the optical aids but I achieve nothing . It is my wish that someone have that miracle that you can transmit to me, thank you very much in advance.

[AstroAndy]

Hi Fabian

Have a look at this video, maybe it'll help.

 

[wimvb]

The MN190 differs from standard netwonians in that the distance between the corrector plate and the primary mirror is critical and should not be changed. That's why the primary mirror doesn't have springs, but only rubber rings between it and the cell. Also, you shouldn't move the secondary mirror up or down the tube.

As a first step, see to it that the secondary is rotated right. There is a small circle on the secondary mirror that should be centered under the focuser draw tube. With my scope it's slightly off along the axis of the tube. This doesn't affect star shape, but  increases vignetting.

Second, align the secondary. Don't touch the central screw which holds the secondary in place. You should only need to adjust two of the three screws that move the secondary.

Finally adjust the primary mirror. Again, only two of three adjustment screws need to be used. Because of the lack of springs, you can't move the primary much. Make small adjustments.

As for tools, I use a barlowed laser for primary adjustment and a cheshire for secondary adjustment.

Finish with a star test.

Hope this helps. 

[wimvb]

10 hours ago, AstroAndy said:

Hi Fabian

Have a look at this video, maybe it'll help.

 

Thanks for the video link.

The MN190 differs from the Comet Hunter in how the secondary mirror is kept in place. There are no hex screws to hold the retainer ring.

I also would never put the scope vertical during collimation. It's all too easy for the secondary to come loose and fall on to the primary. If you search for MN190 collimation here on sgl, you'll come across one such incident.

[FABIAN MARIN]

THANKS, I am watching and reviewing this video, it was so much handled that it is very difficult to start again.
I did everything, but nothing worked. Now I will see everything in detail, but I know there is something ... something that will not work! I hope this time it is not like that!

[wimvb]

Just take one step at a time. Remember: the primary can't be off by much because of the way it sits in its cell. If in doubt, take images of how it looks and post here.

Good luck.

[almcl]

On 27/06/2021 at 17:28, wimvb said:

 Also, you shouldn't move the secondary mirror up or down the tube.

Do you know why this is so critical @wimvb ?  (Not arguing, just seeking enlightenment.)  I only noticed the focuser on my 190MN came with slots to allow it to be adjusted up or down the tube after I had moved the 2ndry down a bit...

And for the OP, you may find this thread (and some of the links others posted) helpful:

 

 

[wimvb]

2 hours ago, almcl said:

Do you know why this is so critical @wimvb ? 

In a standard newtonian, there's only one distance to take care of, and that's from the primary mirror to the focal point. If you move the primary up the tube, you also move the focus outward, and vice versa. Basically, you can move the primary, the secondary, and the focuser up or down the tube in unison, without changing anything.

In a Mak-Newt on the other hand, you have the critical distance from the fixed corrector plate to the primary. And just because the corrector plate is fixed, everything else is fixed as well. The only freedom you have, is tilting the optical components (secondary, primary and focuser), but you should not move things up or down the tube, because then you change the distance to the corrector plate.

Btw, I always have this site up as a good MN190 reference.

https://www.iceinspace.com.au/forum/showthread.php?t=140193

Rereading your thread, I see that I linked to this site before. I still have it open in a tab in my web browser. 😁

Edited June 28, 2021 by wimvb

[almcl]

Thanks, Wim!

[FABIAN MARIN]

HELLO, after trying a crazy thing, which was to remove the primary mirror and with a camera and placed a self-adjusting laser of excellent quality, I tried to hit the center of the secondary mark, it cost me but I succeeded, when I placed the primary, it was a devastating surprise that the laser was pointing so far out that it came out of the primary, I knew it was a little off but not at that level, axis everything, stop! And I told myself this is not for me, and I sent it to the seller to see if he can fix it, collimate it, I hope so, if not I will have to be pestering them for a while more. What a cute telescope it is, but the collimation ........

[wimvb]

Let us know how it is when you get it back.

Good luck!

[Skyline]

You shouldn't be having all this trouble collimating the MN190.

Are you far ?

[Mr Spock]

2 hours ago, Skyline said:

Are you far ?

Argentina I think. It's a shame because there are a few of us who could help if closer.

[Skyline]

Yes, agreed.

[FABIAN MARIN]

What a joy it gives me that this group whom I just met, is offered with such kindness. Thank you infinite, and as soon as I have my telescope, again, and it is my wish that I can fully overcome it, I will know it, and even more so if you cannot recover your potential, truly thanks to all of you!