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MAK CASS Collimation

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#1 Chris Watts

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Posted 16 January 2017 - 11:38 AM

Looking at a mak cass optical tube.  Can a mak cass be collimated?  Are there issues with collimation on MAK Cass scopes?  Since the secondary is impregnated i guess or coated onto the correction place is this an issue at all?

 

Chris



#2 Gofr

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Posted 16 January 2017 - 11:55 AM

It can. I found a very  nice tutorial video on how to collimate a mak on youtube. It's a bit long, but he does an excellent job explaining every detail and how to do it. https://www.youtube....h?v=OlFf1GC70OA



#3 emontano2

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Posted 16 January 2017 - 12:38 PM

 The only problem is when the two mirrors are not well centered in the tube, in that case collimation will be impossible, but the same could happen with other catadioptrics not just Maks.  



#4 Peter Besenbruch

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Posted 16 January 2017 - 02:08 PM

The good news is that the Chinese Maksutovs have Allen headed screws for collimation located on the back of the scope. Thus you can adjust and look without getting off your chair. The bad news is they use two different sizes for their Allen screws. More bad news, the smaller sizes of Maksutov use six screws spaced equally around the back of the telescope. One set is for pushing, the other for pulling. The larger Maks pair the larger and smaller screws. Collimation for the larger Maks is very simple. Point at star (Polaris?). Loosen the smaller screws a lot (a full turn or two). Adjust the larger screws until the defocused star is round while centered in the field of view, preferably at 1x/mm, or higher. Tighten the little screws until they just encounter resistance, then tighten each a bit in turn until modestly tight. That's it.

 

The little guys? That's a different story. Here's some instructions.

 

A final note: Unless you know your diagonal is perfectly collimated, collimate without. Given that a standard diagonal reverses one of the axes, it's also less confusing to collimate without the diagonal.


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#5 Max Power

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Posted 16 January 2017 - 08:09 PM

Much easier to do it in the house with a Hubble star flashlight.
It has 5 'stars', I put plastic tape over 4 of them. Then all you need is about 40 feet of straight clear room to do the collimation or do it outside. The stars move, your flashlight won't.

Edited by Max Power, 16 January 2017 - 08:10 PM.


#6 Don Taylor

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Posted 16 January 2017 - 10:05 PM

Looking at a mak cass optical tube.  Can a mak cass be collimated?  Are there issues with collimation on MAK Cass scopes?  Since the secondary is impregnated i guess or coated onto the correction place is this an issue at all?

 

Chris

This depends on which Mak Cass scope - not all brands and designs are the same.  The Meade ETX series uses collimation screws on the primary only.  Some others (e.g. RuMaks and Klevstov Maks) may have collimation adjustments on the primary, secondary, and focuser. While others have no user collimation adjustments at all.

 

The more adjustments available - theoretically the better collimation can be achieved. Unfortunately the presence of these adjustments increases the likelihood that the telescope may be poorly collimated.

 

The ETX scopes were easy to collimate well and hold collimation. - but the alignment of the secondary/corrector and the focuser are not user adjustable and the level of collimation is determined by the manufacturing tolerances. My two were apparently well made so precise collimation can be achieved.  

 

I have no personal experience with Questar, Synta, or other Gregory-Maks, only the ETX 90 and 125 and the Vixen VMC200 style Field/Klevstov Maks.


Edited by Don Taylor, 16 January 2017 - 10:07 PM.


#7 Darren Drake

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Posted 17 January 2017 - 04:16 PM

I have found that de rotating the corrector lens on an etx 125 and also similarly on some refractors can improve collimation. Very slight changes occur as the lens assembly is rotated. This can have it fall in an improved alignment if checked over several orientation positions..

Edited by Darren Drake, 17 January 2017 - 04:52 PM.

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#8 aeajr

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Posted 23 January 2017 - 06:51 PM

Just got an old ETX 125 and was wondering about this.

 

Do I use the same collimation cap that I use for my Orion XT8i.  Will the mirror be center marked?  With a hole for the focuser I am not sure what I would be using as a reference.

 

Can I check collimation using the defocused star test that I use for my Dob


Edited by aeajr, 23 January 2017 - 06:59 PM.


#9 Peter Besenbruch

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Posted 23 January 2017 - 08:42 PM

You eyeball it straight through. I don't remember if the ETX had a flip mirror,but if so, flip it out of the way and look through the back end. If it didn't, but came with a visual back, remove it, and eyeball it. You can get pretty good collimation in the day time. There probably are directions floating around out there, somewhere.


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#10 AUricle

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Posted 24 January 2017 - 12:18 AM

You eyeball it straight through. I don't remember if the ETX had a flip mirror,but if so, flip it out of the way and look through the back end. If it didn't, but came with a visual back, remove it, and eyeball it. You can get pretty good collimation in the day time. There probably are directions floating around out there, somewhere.

Here's a daylight indoor method:

 

http://www.robincasa...ro/collimation/



#11 Marcsabb

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Posted 24 January 2017 - 03:34 AM

With my Intes I can collimate both the primary and the secondary, although the primary need a tweak usually only after disassembling the cell. The secondary is collimated like a SCT, very easy to do with a bright star. One of the advantages of a Rumak type, I guess...



#12 rogan

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Posted 24 January 2017 - 11:16 AM

Here's a look at the back end of an ETX 125 and the three adjustment screws. To get at them requires removing the plastic housing. or in my case the Wegat adapter plate.

 

IMG_0369.JPG

 


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#13 aeajr

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Posted 24 January 2017 - 12:26 PM

Thanks Regan.

#14 azure1961p

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Posted 27 January 2017 - 10:58 PM

Ed,

 

I will say this, collimating a mak for me took some patience and a cool head. Both my SCT and Reflector were easier. The deal with those mak screws is you want noth, push and pull to not be OVERLY tightened one way I'd the other. Each has to have this gentle tweak accommodating for the adjustment you just made .  Both push and pull want their own attention to give the resultant equalibrium between them act as the SET for the adjustment.

 

It's not fifficult. I only ran into trouble treating it like I was collimating my reflector.

 

Good luck.

 

Pete



#15 aeajr

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Posted 27 January 2017 - 11:59 PM

Does a defocus on a bright star work with the Cats?   I use this in my Newtonian/Dob to do a quick confirmation that comllimation is at least acceptibly close.   Can I do the same with the Mak?

 

Will my collimation cap from my Newtonian work with the Mak?  clearly there is no center dot for me to see.


Edited by aeajr, 27 January 2017 - 11:59 PM.


#16 emontano2

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Posted 28 January 2017 - 12:40 AM

You can check the collimation of a Mak with the star Polaris, it is very similar in the way of checking with a dob ( I have both), the inside and outside focus pattern should be centered and have the same balance or proportions.

However, the difference is that a dob can and should be collimated with a star, but for many types of Maks this is not possible, because the set of screws in the back of the scope require a much different approach.

I found that the best way to collimate a Mak is to bring it outside during the daylight and place a piece of white paper in the front of the scope with tape, in order of creating a white bright screen, then you go to the back of the scope and without the visual back look through the opening and center the image of the mirror accordingly, going back and forth with the collimating screws. It is not difficult, it is a matter of practice, can be done also inside your home  during the night with the scope facing a bright source of light just don't forget the piece of paper and don't try to collimate it with a diagonal or prism inserted, some times those are misaligned and will frustrate your efforts.


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