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More mak newt collimation questions/help needed.

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24 replies to this topic

#1 chunkymak

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Posted 05 August 2021 - 01:08 PM

Hi all from the grey skies of the U.K. 
First off, I’m new to this site, so please go easy on me! 
I think that I’m going to have to bite the bullet (so to speak) and collimate my Intes mn78. I purchased it second hand, and overall, it’s in fair condition. The seller did inform me that collimation might be needed. It has at some point been fitted with a Moonlite focuser. To be honest, it also appears that someone has used the wrong size screwdriver to adjust the secondary adjusting screws and, as a result, the screws will need  replacing. It also appears that the meniscus has been moved at some point. I’ve tried to get it under the stars to check it optically (cloudy nights at present!!)  and will not adjust anything until I carry out a star test. If all looks ok, I will CAREFULLY  replace the screws on the secondary holder and problem solved. If I do have to collimate from scratch, am I correct in that (In this order)  the meniscus will need to be centred on the optical axis of the OTA.  I will also have to centre the focuser over the secondary and square the focuser in relation to the OTA. Please correct me if I’m wrong, but I assume that once the steps mentioned previously are completed correctly, getting the secondary and primary mirrors lined up is pretty much the same as a Newtonian. Any advice very much appreciated.  P.S. Although I joined the site some years back, due to work/life commitments, I have only just started to have the time to get back into observing seriously. Now that I have more time on my hands, I want to sort out this potentially fine scope before the winter nights start drawing in.

 

Thank you all, and clear skies (one night soon!)
 


Edited by chunkymak, 05 August 2021 - 01:53 PM.


#2 luxo II

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Posted 06 August 2021 - 06:01 AM

Ok...

 

In this case, once you have the replacement screws I'd lift the whole secondary and diagonal out before you replace the screws; it would be a tragedy if something untoward happened (eg the secondary falling off and hitting the primary. Personally I would use stainless allen-head grub screws (see accu.co.uk) not "Bobs Knobs".

 

You also need:

 

- a $2 plastic hand-spray bottle, a litre of 100% pure isopropyl alcohol (industrial solvent suppliers, its cheap) and a bottle of 100% demineralised water. Fill the hand-spray with a 50/50 mix ready for the final clean during reassembly. You'll also need half a dozen Q-tips or the cotton pads women use to remove makeup.

 

- a bottle of ladies nail-polish (colour not important),

 

- a business card, a pair of scissors to cut it, tweezers and/or a toothpick (you'll see why at step 6).

 

1. Place scope on a bench with something soft covering the work area, eg a thick plush towel in case you drop something expensive. Put a clean well-washed tea towel over that so small screws etc wont get lost in the towel, and the scope on that. I have done this on a carpeted floor, that way there's nowhere for anything to fall.

 

2. The front ring with all the holes is cosmetic, serves no real purpose. Remove 3 screws and lift off.

 

3. Under the ring you should find three half-moon metal tabs with small retaining screws holding the corrector in place. Before you undo these, place a piece of tape on the cell in line with the focuser assembly, and put a pencil mark on the ground edge of the corrector (not the polished surface !!) so you can replace it in the same orientation.

 

If you study the corrector carefully you should find three small shims between the glass and the metal of the cell, these are crucial - they allow for differential expansion/contraction of the cell without crimping the corrector - localised force of metal on glass is a good way to produce a clamshell fracture or worse, break the corrector.

 

Loosen the 3 screws (they should only be finger-tight), turn the half-moons and lift out the corrector and put it aside. Put the shims somewhere safe too. if one is not looking so good you can make a replacement by cutting up a business card. 

 

Park the OTA somewhere safe.

 

4. Now deal with the secondary mirror assembly, aiming to replace the screws and put the diagonal back together in the same orientation. Study the assembly; the ones I saw have a knurled ring around the outside of the secondary mounting which, if loosened, allows you to rotate the secondary with respect to the corrector, and the three little screws are for adjusting tip/tilt. The centre bolt adjusts its position along the optical axis. It is advisable to measure the space between the back of the cell and the mounting in the corrector with callipers so you can get this correct again when re-assembling.

 

5. Clean the optics - including primary mirror - by spraying hard with the water/alcohol mix - not wiping or scrubbing with anything - and allow to drain. The last few drops can be removed by touching each drop with a Q-tip or corner of a cotton pad, if you can do this without touching the glass there will be no lint left behind. 

 

6. Reassemble and place in a warm place - in the sun on a hot day is good, or near a radiator - to drive out the last of the water/alcohol mix. Don't worry if the glass fogs on the inside, it will evaporate later. Don't use a fan - this will blow lint onto the optics.

 

When replacing the corrector in its cell:

 

A. make sure the little card shims are in between the glass and the mirror - both under the bottom edge, as well as the side, so glass does not touch metal. This can be quite fiddly and you may need tweezers or a toothpick to manipulate the shims.

 

B. there are no adjustments to centre the corrector laterally in the cell - the shims take care of that. 

 

C. turn the little half-moon tabs so they are over the edge of the corrector, securing it. Tighten the little screws to hold these in place just finger-tight. if you over tighten these, you will strain the corrector which can have catastrophic effects on image quality. To stop these screws working loose, apply a dab of nailpolish over the screw, it is easily chipped off again if you need to redo all of this.

 

7. Collimation. This works as per any newtonian, ie rotate the cell to get the primary centred on the secondary and then adjust the tip/tilt screws.

 

The last part - given the focusser was replaced - is to establish whether the focusser is co-axial with the secondary mirror, it may have to be moved along the OTA. You'll need a cheshire or laser collimator to check this.

 

8. When all done, point the OTA down somewhat (stops water running inside) and spray the outside of the corrector again to take off any fingerprints, dust or lint.

 

9. Replace the outer ring with all the holes.

 

10. After several nights use when you are thoroughly satisfied with the collimation, apply a dab of nail polish to the secondary adjustment screws to stop them moving inadvertently. 

 

With practice it is possible to clean the surfaces as free of lint and dust as Intes made them, and it's spectacular in the "flashlight test".


Edited by luxo II, 06 August 2021 - 06:29 AM.


#3 chunkymak

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Posted 06 August 2021 - 06:35 AM

First off, thank you Skylab for taking the time out to reply-very much appreciated.

Fortunetely, I already have a bottle of 100% iso and d water. I have dissembled optics before (7” Meade Mak and Celestron C8) successfully. My main concern (apart from the damaged screws) is the correct rotation of the corrector plate (not sure if it’s been moved-if so, how do I set it back to factory setting?  And also the optical alignment of the corrector to the centre of the primary mirror. Do you (or anyone else) know if the corrector plate is shimmed from underneath to centre it perpendicular to the primary? As I understand it, the centre of  corrector plate has to be pointing to the centre of the primary mirror-the same principle as adjusting a secondary mirror (with laser or Cheshire) to hit the centre of the primary mirror. If this has been tampered with, I’ll need a method of checking the alignment.  Also, I read about “squaring the focuser” on a mak newt. Does this mean the X+Y axis as well as centring over the secondary- the focuser has tilt screws fitted to allow adjustments in two axis, back and forth and side to side. Apologies if this a bit long winded, it’s just that the more I learn about optics, it seems the less I know. I just want to make sure that I’ve done my homework before taking things to bits. 
 

Once again, thank you.



#4 luxo II

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Posted 06 August 2021 - 06:56 AM

Sorting out the rotation of the corrector is something you cannot do DIY as it is normally done at a lab with a DPAC optical test bench and interferometer.
 

And it may not matter much. If the scope has a good star test without obvious asymmetry at high power don’t worry about it.  Most of the intes glass seems to have good circular symmetry; defects if any tend to be zones or slight spherical aberration. 
 

There are also no tilt adjustments for the corrector; the mechanical assembly of the cell by Intes is accurate so nothing needed (don’t ask how they managed it). The only thing to watch is that if replacing a shim, replace all three so they’re all the same thickness, that way you won’t create any tilt error.

 

Squaring the focuser means getting the focuser coaxial with the optical axis. If it has been replaced or futzed with, it’s possibly not in the right place. Intes used a base plate for the focuser with slotted holes allowing it to slide lengthwise along the ota either way by a cm or two. You’ll need a Cheshire or laser collimator to check this (eg the Howie Glatter). Basically same as any Newtonian except you move the focuser, not the secondary mirror.


Edited by luxo II, 06 August 2021 - 07:17 AM.


#5 chunkymak

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Posted 06 August 2021 - 07:48 AM

Thank you once again Skylab. You’re a star!  I’m going to follow your advice step by step. I’ll report back when I have sorted out any issues with the scope and tested it under the stars. It’ll probably take a few weeks, as the weather is quite poor at present and I need to order some new screws and get everything together before I start. Hopefully I can get everything spot on and start enjoying what these scopes are known for-excellent planetary/Luna and double star views.

 

clear skies to all.



#6 TG

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Posted 09 August 2021 - 03:58 PM

Did you review this thread?

https://www.cloudyni...wt-collimation/



#7 chunkymak

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Posted 10 August 2021 - 09:19 AM

Hi TG

Just read it through-I now have a better understanding of the process of collimating my mak newt, thank you. Also a big THANK YOU to everyone who has taken the time to reply to my questions. 
Clear skies and big eyes!
 



#8 chunkymak

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Posted 10 August 2021 - 09:33 AM

BTW, I managed to find some replacement Allen head grub screws For my Intes Micro MN78 (in my Astro bits n bobs box-result!) and I’ve managed to get a fine file in the slot of the central secondary screw/bolt. I put the OTA horizontally on a blanket, then used my Giotto air blower to remove any brass filings. Seems to have worked. At present, the weather is  showers/rain/sunshine-not good for testing out the scope. Hopefully, the predicted high pressure weather front will arrive over where I reside soon. Itching to see what this scope can do. 
Once again, thank you all.



#9 Jeff B

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Posted 10 August 2021 - 09:39 AM

You have a MN78!?



#10 chunkymak

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Posted 10 August 2021 - 09:39 AM

FD294F37-1E5B-4940-BD70-971EC36A937C.jpeg

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#11 chunkymak

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Posted 10 August 2021 - 09:55 AM

Hi Cosmos

Yes, got it some time back. As I stated in an earlier post, overall, it appears in fair condition. One or two minor scratches on the paintwork (not bothered) and the collimation has already been “adjusted” It came fitted with the Moonlite focuser. All of the optical surfaces look pretty good. I have just (today) CAREFULLY replaced the  three grub screws that allow for secondary mirror adjustment. I was going to leave them well alone, but the more I thought about it, the more I realised that it’s better to replace them now, rather than try to replace them after a couple of cold/damp U.K. winters. There were a few nervous moments trying to get the little things out-but all good now (I hope!) 
Roll on clear skies!


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#12 chunkymak

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Posted 10 August 2021 - 10:05 AM

F28DA7C3-5971-4B13-A5E9-149DBE7310BE.jpeg CDBAA5FC-8427-4CEC-B503-9925843C9B46.jpeg

The rear fan was missing from the scope when I got it. The seller (or someone) had attached a very small fan to the side of the OTA. I’m sure I can fabricate something that will work and approximate the original  (the dogs feeding bowl’s made of stainless steel and looks about the right size!!) 
 

woof woof!!


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#13 chunkymak

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Posted 10 August 2021 - 10:11 AM

9D5A3706-0511-4955-BCC4-53372BEC356A.jpeg

 

Apologies to all for the various pictures over several posts-still finding my way around the site.


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#14 chunkymak

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Posted 10 August 2021 - 10:13 AM

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#15 chunkymak

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Posted 10 August 2021 - 10:24 AM

Here’s a picture of some of the gang!
 

From the back, left to right Meade LX10, Meade 7” Mak,  Meade 7” Mak  (yes 2, I know, I know!!) Big binoculars anyone??!!  Then (the slim whit tube) Orion Optics (U.K.) OMC140, Celestron C8, Intes-Micro Alter M603.

And in the front row, Meade’s mighty ETX90 and an Intes MK67. There is a Meade ETX125 hiding in my observatory (shed) which made a strange noise when I went to power it up recently-it seems to have blown a fuse or something. Probably best to defork it to be honest.
Anyway, this lot plus the MN78 and a few others that are not Catadioptrics and thus are not allowed on this blog!
 

peace


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#16 Jeff B

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Posted 10 August 2021 - 01:38 PM

Mak attack!!

 

That MN78 looks wonderful.  I really like the spanner grooves added to the secondary holder, allowing you to keep it in place with a spanner while tightening the outer nut. waytogo.gif

 

There was some carping about the NM58, 68 and 78 as, at those focal ratios, there is little coma.

 

So why do an F8 MN?  Well, like the joke about male dogs, "because they can", but also, no annoying spiders and at F8 the scopes will be essentially coma free, with lower astigmatism and notably less field curvature than a newtonian of the same focal ratio.

 

Good stuff!

 

Jeff.  



#17 chunkymak

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Posted 10 August 2021 - 03:22 PM

Thanks Jeff.

 

If I remember correctly, the central obstruction is around 13% (might be 16%-I’ll have to look it up)  As those numbers are very small for an obstructed system, I’m hoping it will perform as advertised-essentially an observatory class 7” apochromatic Luna/planetary/double star scope. I know that the Meade 7” maks have a large central obstruction (take your pick on how big-there seem to be many opinions) and are a different design, but when cooled to ambient temperature, they perform beautifully (to my eyes) Anyway, I know that it will be a challenge to collimate my MN78 (I do enjoy a challenge) I just hope that I can collimate it correctly, and once collimated, only a minor tweak every now and again. We shall see!
 

Thank you for your kind words.



#18 stuart keenor

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Posted 10 August 2021 - 04:55 PM

Great scope ! Congratulations my friend paul Cruickshank inns based in Yatey Hampshire has a mn78 paul is the leading man on all things maksutov Newtonian and cassegrain, he’s done loads for me over the years ( full refurbished my 10” mak newt spring loaded the secondary screws too👍), if you need any further advice contact paul 👍I’m sure he’d be happy to help
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#19 chunkymak

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Posted 10 August 2021 - 05:15 PM

Great scope ! Congratulations my friend paul Cruickshank inns based in Yatey Hampshire has a mn78 paul is the leading man on all things maksutov Newtonian and cassegrain, he’s done loads for me over the years ( full refurbished my 10” mak newt spring loaded the secondary screws too), if you need any further advice contact paul I’m sure he’d be happy to help

Thank you Stuart, I might just do that. In fact, thanks to all that have replied to me. I did try to get the MN78 checked over some time ago by someone in the U.K.  They seemed quite keen until I said the words“Maksutov Newtonian” they then informed me that they were difficult to service and weren’t interested in taking it on. When that happened, it didn’t inspire confidence in me. I feel a lot more at ease now I know there are people out there willing to give help and advice.

 

Thank you all.



#20 Jeff B

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Posted 10 August 2021 - 10:44 PM

Great scope ! Congratulations my friend paul Cruickshank inns based in Yatey Hampshire has a mn78 paul is the leading man on all things maksutov Newtonian and cassegrain, he’s done loads for me over the years ( full refurbished my 10” mak newt spring loaded the secondary screws too), if you need any further advice contact paul I’m sure he’d be happy to help

Stuart, how in the heck are you all doing!

 

Jeff



#21 chunkymak

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Posted 11 August 2021 - 09:26 AM

Hi all

 

As it was such a beautiful morning here in my part of the world today, I decided to have a look at what's what in regards to collimating my Intes Mak Newt. When I looked down the focuser tube (using a collimation cap) I could see that the focuser was not centered over the secondary mirror. To cut a long story short, as I had a morning to myself, I decided to tweak the scope. I used a collimation cap and a Cheshire tube. TBH, it was tricky-that secondary is really small! I ended up centering the focuser over the secondary, then tweaked the secondary adjustment screws to get everything as concentric as I could. I then had to make a very small adjustment to the primary mirror.  I'm not claiming that it's spot on, but for now, it should give reasonable results and I can get it under the stars and test it out. I still intend to follow the good advice you have all given me (if needed) I did do a visual check on the secondary holder while I was adjusting the focuser, it looked perpendicular(in line)with the optical axis so I've decided to leave alone for now. Anyway, I'm hoping that I got lucky. We shall see. Unfortunately, I'm having to work late every evening this week. I have the weekend free and will report back. 

 

Once again, thank you to all that have helped, it is very much appreciated. 

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#22 chunkymak

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Posted 11 August 2021 - 10:04 AM

BTW,  I mentioned in a previous post that someone had fitted a small fan to the side of the OTA just above the main mirror. When checking over the scope earlier, I noticed 3 holes approximately 20mm each in diameter, have been cut/drilled into the OTA opposite where the fan was. These holes appear to have been cut/drilled by the factory. All 3 holes have been fitted with a mesh filter behind them. The same for the hole where the side fan was. Cut/drilled hole fitted with a mesh filter.  I’m pretty sure this was done by the manufacturer, as there are no tell tale aftermarket marks anywhere. The edges of each hole are smooth and have the same paint as the rest of the OTA. I did try several times to download some photos from my phone (files too big) Anyone know if this is a standard modification? I have looked at a few images of other MN78’s but never noticed it before. I will try and get some photos tomorrow.

 

P.S. I took the pictures of the secondary with my phone -very tricky to say the least! The lines on the secondary on the first image are a reflection of a bath towel that just happened to be in the line of the OTA-nothing to do with a Foucault test!!! The second image (lower) was taken with the Cheshire collimation tube in place.

 

clear skies.


Edited by chunkymak, 11 August 2021 - 10:12 AM.


#23 Jeff B

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Posted 11 August 2021 - 08:01 PM

Hi all

 

As it was such a beautiful morning here in my part of the world today, I decided to have a look at what's what in regards to collimating my Intes Mak Newt. When I looked down the focuser tube (using a collimation cap) I could see that the focuser was not centered over the secondary mirror. To cut a long story short, as I had a morning to myself, I decided to tweak the scope. I used a collimation cap and a Cheshire tube. TBH, it was tricky-that secondary is really small! I ended up centering the focuser over the secondary, then tweaked the secondary adjustment screws to get everything as concentric as I could. I then had to make a very small adjustment to the primary mirror.  I'm not claiming that it's spot on, but for now, it should give reasonable results and I can get it under the stars and test it out. I still intend to follow the good advice you have all given me (if needed) I did do a visual check on the secondary holder while I was adjusting the focuser, it looked perpendicular(in line)with the optical axis so I've decided to leave alone for now. Anyway, I'm hoping that I got lucky. We shall see. Unfortunately, I'm having to work late every evening this week. I have the weekend free and will report back. 

 

Once again, thank you to all that have helped, it is very much appreciated. 

You're a tiny bit off, mostly front-to-back, but that's easy to adjust with the ability to slide the focuser.

 

Jeff



#24 chunkymak

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Posted 12 August 2021 - 04:57 AM

Thanks Jeff

 

I noticed it myself when studying the photos. I will try my best to “tweak” it.  It was a good experience trying to understand what was what in regards to collimation and adjustments. What I found was, the focuser need only move a slight amount to affect other things. I think this is due to the very small secondary-it has to be spot on. Anyway, I will give an update on my progress (if anyone’s interested) ASAP. Unfortunately, the blue, Sunny skies of yesterday are no more. Rain/showers and grey skies. Oh well, at least it’s warm rain!

 

Once again

Thank you.

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Edited by chunkymak, 12 August 2021 - 04:59 AM.


#25 chunkymak

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Posted 12 August 2021 - 06:04 AM

Hi all

 

These are the fan and ventilation holes in the OTA on my MN78. They are located just above where the primary mirror sits. When I first got the scope, a side fan was fitted (not working) I assumed that it was added on by the previous owner. I removed it from the scope (still have it)

I’ve looked at various images of other Intes Micro Mak newts online, never seen these before.

It was originally fitted with a rear fan as standard which was missing from the scope when I acquired it. I intend to refit a rear fan, and while I’m at it, repair or replace the side fan. I’ve no idea what, if anything was fitted over the three holes opposite thee side fan. All of the ventilation holes have had a fine mesh fitted internally (you can see it if you zoom in) Anyone got a link to any images or perhaps something similar?  Any help appreciated. BTW, I’m pretty sure the side fan and the ventilation holes were put there by the manufacturer. As I understand it, most of the Russian optical manufacturers are not making scopes for the consumer market anymore.It would be nice to get the scope back to it’s former glory. 

Once again

Thank you all .F38B3A16-5B80-4806-8539-EE97FBE8104B.jpeg 4579FAAC-463D-48DD-849E-2234260165A9.jpeg

 


Edited by chunkymak, 12 August 2021 - 06:06 AM.



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