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Collimation and a Mak-Newt

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#1 Chaz

Chaz

    Mariner 2

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Posted 17 October 2005 - 05:14 PM

Hello everyone:

Could someone help me understand a few things about collimating a Maksutov-Newtonian? I was under the impression that like a Maksutov Cassegrain the meniscus lens is fixed at the factory and does not need collimation like an SCT. However, I've read several CN reviews that mention the difficulty of collimating one. I understand that they are superb telescopes optically, but suffer from long cool down times and problematic collimation.

Thanks alot,

Chaz
TV102
Nexstar 8i
10" Discovery Dob

#2 sixela

sixela

    Hubble

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Posted 17 October 2005 - 05:59 PM

It's necessary for the optical axis to lie perpendicular to the corrector, which means that secondary offset has to be perfect (which also means the primary and secondary have to be well placed in relation to one another, that the focuser is shimmed correctly, etc.). Same issue as on the SN (on which, fortunately, Meade seems to have implemented correct offset away from the focuser in the secondary holder).

In contrast, on a Newtonian, you can have good collimation with an imperfectly squared focuser and an imperfectly placed secondary - you'll end up with an optical axis that's not exactly along the tube axis and a fully illuminated field that's not of optimal size, but that's all.

#3 Matt Looby

Matt Looby

    Apollo

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Posted 17 October 2005 - 07:34 PM

Hi Chaz,

Regarding collimation, exactly like any newtonian but
simpler because the secondary is set on the optical axis
within the corrector lens.

I use an Intes Chesire sighting tube for the secondary.
(simple).

Move the focuser forward or back a tiny bit until secondary
is perfectly centered in the crosshairs. (3 mins.)
Make adjustment to seconday so reflection of the rear of tube is centered in secondary. (3mins)

I installed a Catseye collimation reflective triangle onto
center of primary mirror.


Use Catseye sight tube to adjust primary (3 minutes).
Collimation is now 99% complete and good enough for any
serious planetry work. Collimation will remain intact unless the optics are removed or subjected to stong vibrations.
I just moved 1200 miles and my MN86 lingered in the back of a rental van, sujected to all kinds of bumps etc, and to my amazement it needed no collimation-still dead on!

Since all my optical instruments are stored outside under a dry roof, cool down has never been an issue. Incidently I would never recommend shocking the optics of any telescope by exposing it to 20-30+ temperature variance. This scope deserves to be ready to go at a moment's notice.

I should note that I am not a marathon observer. I can't observe and make renderings for hour upon hour. I am usually good for 1-2 hours tops.

The Mak-Newt I own has ledgendary optics and it will out perform or at least equal any optical instrument in it's
aperture class.

I highly recommend the Intes-Micro, or Intes Mak-Newts.

I hope this helps!

Thanks,

Matt Looby

#4 matt

matt

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Posted 18 October 2005 - 04:11 AM

here's what I wrote to a guy I'm about to trade my mak-newt to:
"Yes collimating this scope needs some getting used to. It collimates like a regular Newtonian (fortunately enough, there is nothing to collimate the Maksutov corrector!). The difficulty arises from the fact that on a Newtonian, there is a spider, and you can hold on to the secondary's mount while you screw/unscrew to collimate. Here you can't hold the secondary's support, it's just stuck in the middle of the corrector, so when you screw/unscrew, you tend to rotate the whole secondary! My trick is I use a fondue fork (!) plucked on screws A and B while I adjust screw C, this keeps the secondary from rotating and then it's not different from a regular Newtonian. I would also add that both primary and secondary hold collimation quite well, after a (not too bumpy) 2-hour drive there is no need to recollimate."


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