collimating 127 mak

[davekelley]

Hi everybody.  Just after a bit of general advice. I have a new scope skywatcher 127mak.  So far I've been able to see amazing detail on the moon but the sky is mostly cloudy so nothing else just yet.  Looking into a cheshire type collomation cap all seems great but I also have a laser collimator and that tells me all is out of collimation by a mile!  Now I do not want to start using the laser and adjusting the collimation I think I could make things a lot worse and it could just be a rubbish laser collimator I'm using?   Are lasers not practical with a Mak?  Should I wait till I can  do a star test?  Whilst I am here, will upgrading to a dielectric diagonal be worth the cost or should I save my money?

Thanks

Dave

[John]

Definitely wait until you do a star test and don't be tempted to fiddle unless that shows something is amiss.

Mak-cassegrains generally maintain their collimation well. Laser collimators are often out of collimation themselves plus, for scopes with perforated primary mirrors such as the mak-cassegrain, the star test is a much more reliable guide.

A dielectric diagonal will be an improvement over the stock item but don't expect startling improvements - the optical improvements are subtle, mostly, I feel but the better build quality and, ideally, a compression ring eyepiece fitting are worth having.

As long as the secondary shadow is central within the expanded airy disk of a star (Polaris is a good one to choose) inside and outside of focus, your collimation is good. Let the scope cool fully before star testing and use around 150x - 200x magnification.

 

[John]

I found this image of the star test from a 127mm mak-cassegrain in good collimation from an Italian review so this is what to look for outside (extra) and inside (intra) focus:

 

[johninderby]

Laser colimators are pretty useless for colimating a mak. Because the seconday mirror surface is curved just the smallest misalignment or slop in the diagonal or the laser itself will throw the beam way out.

As mentioned above star testing is the best way to check colimation with a mak.

Edited May 20, 2019 by johninderby

[RT65CB-SWL]

Hi Dave.

1. Have you checked the collimation of your laser? - some of the cheaper ones have little rubber plugs and underneath should be some screws or grub-screws. You will need to make some form of 'V' block - I recommend you watch this first... 
2. Does it appear out of collimation with or without a star diagonal attached?  - sometimes star diagonals can be out of collimation too!
3. There are YouTube videos on how to collimate Mak's and SCT's + other internet sites, with or without video.
4. As @John says, a dielectric will be an improvement. Below are some images of my 're-modded' Meade ETX105 with an Altair Astro 2" SCT star diagonal [1] and a 1.25" star diagonal attached to the visual back and ETX to SCT adaptor ring [2]. I can also attach other SCT accessories to the adaptor ring [3]... and without the adaptor ring [4].

[1]            [2]    

[3]             [4]

Edited May 20, 2019 by Philip R

[Cornelius Varley]

1 hour ago, davekelley said:

Hi everybody.  Just after a bit of general advice. I have a new scope skywatcher 127mak.  So far I've been able to see amazing detail on the moon but the sky is mostly cloudy so nothing else just yet.  Looking into a cheshire type collomation cap all seems great but I also have a laser collimator and that tells me all is out of collimation by a mile!  Now I do not want to start using the laser and adjusting the collimation I think I could make things a lot worse and it could just be a rubbish laser collimator I'm using?   Are lasers not practical with a Mak?  Should I wait till I can  do a star test?  Whilst I am here, will upgrading to a dielectric diagonal be worth the cost or should I save my money?

Thanks

Dave

The only way to collimate a Mak is by either a star test on a medium magnitude star or by using an artificial star.  Collimating with a laser can give misleading results, the telescope can be perfectly collimated but the laser says otherwise.  

[Cosmic Geoff]

My 127 mm Mak has never needed collimation, ever.  Read the advice above. And bin the laser.

[Alan64]

This 90mm Maksutov upon my larger alt-azimuth, fell over one day.  The telescope itself did not hit the floor, as the girth of the mount prevented that...

It's not my own, a relation's, but I'm the only one who has used it in an astronomical manner.  I don't know if it's out of collimation from the factory, or as a result of happenstance, but it is off a bit according to my collimation-cap.

There are instructions online, and the process akin to a Chinese finger-puzzle for those who have yet to attempt the procedure, including myself.  But I feel responsible in this instance, so I get to have some fun.

Of the three mirrored designs of telescopes commonly encountered within the marketplace -- Newtonians, Maksutovs, and Schmidts -- the Maksutov is the most difficult to collimate, with the Newtonian running a close second.  A Schmidt is not necessarily a cake-walk however, but is the easiest of the three.

If you have a 1.25" diagonal that came with the kit, and are wanting to replace it with another 1.25", I humbly suggest a star-prism, rather than a star-mirror(dielectric), like this one...

https://www.365astronomy.com/Celestron-Diagonal-Star-1.25-in.html

The Lacerta appears identical, but I would write or telephone first to ensure that it is in fact a star-prism... 

https://www.365astronomy.com/Lacerta-Star-Diagonal-1.25-inch.html

Then there's this one, and not for too terribly much more than an entry-level dielectric...

https://www.firstlightoptics.com/diagonals/takahashi-125-diagonal.html

Edited May 20, 2019 by Alan64

[RT65CB-SWL]

47 minutes ago, Alan64 said:

This 90mm Maksutov upon my larger alt-azimuth, fell over one day.  The telescope itself did not hit the floor, as the girth of the mount prevented that...

It's not my own, a relation's, but I'm the only one who has used it in an astronomical manner.  I don't know if it's out of collimation from the factory, or as a result of happenstance, but it is off a bit according to my collimation-cap.

There are instructions online, and the process akin to a Chinese finger-puzzle for those who have yet to attempt the procedure, including myself.  But I feel responsible in this instance, so I get to have some fun.

Of the three mirrored designs of telescopes commonly encountered within the marketplace -- Newtonians, Maksutovs, and Schmidts -- the Maksutov is the most difficult to collimate, with the Newtonian running a close second.  A Schmidt is not necessarily a cake-walk however, but is the easiest of the three.

If you have a 1.25" diagonal that came with the kit, and are wanting to replace it with another 1.25", I humbly suggest a star-prism, rather than a star-mirror(dielectric), like this one...

https://www.365astronomy.com/Celestron-Diagonal-Star-1.25-in.html

The Lacerta appears identical, but I would write or telephone first to ensure that it is in fact a star-prism... 

https://www.365astronomy.com/Lacerta-Star-Diagonal-1.25-inch.html

Then there's this one, and not for too terribly much more than an entry-level dielectric...

https://www.firstlightoptics.com/diagonals/takahashi-125-diagonal.html

At least I am not the only one that has a had mishap/accident with a Mak!

Mine is too, I think, is slightly off a bit. My ETX105 hit grass/lawn and damaged two mounting points and cracked the ABS flip-mirror cell.

One thing you could try, you can give it a gentle shake and if you hear a slight knock. The locking ring that slides the primary mirror on the baffle tube sometimes work loose. If you can remove the meniscus cell/corrector plate, (making note of its orientation for re-assembly), may need a slight tightening up. This is what I did with mine, before the 're-mod', (photos in my earlier post), and have not touched it since. If in doubt ask someone at your local astro-society/club who can fix it. 

[Alan64]

10 minutes ago, Philip R said:

At least I am not the only one that has a had mishap/accident with a Mak!

Mine is too, I think, is slightly off a bit. My ETX105 hit grass/lawn and damaged two mounting points and cracked the ABS flip-mirror cell.

One thing you could try, you can give it a gentle shake and if you hear a slight knock. The locking ring that slides the primary mirror on the baffle tube sometimes work loose. If you can remove the meniscus cell/corrector plate, (making note of its orientation for re-assembly), may need a slight tightening up. This is what I did with mine, before the 're-mod', (photos in my earlier post), and have not touched it since. If in doubt ask someone at your local astro-society/club who can fix it. 

Sorry to hear of that.  Have you either repaired the flip-mirror cell or bypassed it with the camera-port? 

[RT65CB-SWL]

5 minutes ago, Alan64 said:

Sorry to hear of that.  Have you either repaired the flip-mirror cell or bypassed it with the camera-port? 

Hi @Alan64... this is what my 're-modded' ETX105 now looks like...

12 hours ago, Philip R said:

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