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Collimating refractor

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#1 dron2015

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Posted 21 October 2019 - 08:11 PM

Dear fellow astronomers,

 

May I have quite a newbie question?

 

My main caliber has got some dust on the inner side of the objective recently (do not ask) and recently has got new focuser. it seems that I will have to remove the lens cell, clean it and when assemble back. so the scope surely will lose its collimation. Previously, I have not performed such an art. So, here are my questions:

 

1. What tools exactly do I need to have to collimate my refractor?  I have read a couple of CN topics re collimating refractors, including "adventures in Refractor Collimation", so I have a feeling that I have high level understanding (in general) of the steps to undertake. But what would be the best options for the tools? Reasonably priced - not sure if I want to go such great instruments as Howie Glatter mostly due to its high prices - for me it is (hopefully) going to be one time procedure, so do not want to expense a lot of funds, unless, you advise against this approach.

1.1. Laser collimator to ensure that focuser is aligned.  Which exactly?

1.2. Cheshire collimating tool, to fine tune the objective. Which exactly?

1.3 something else?

Or it is not a good idea for a newbie to explore this route and better to seek for help at local astronomy association experts?

 

2. Also, how do you remove the dust in between of the lenses in the cell? I am not going to disassemble the cell, but since the dust somehow appeared there - perhaps it is possible to remove? vacuuming or vice verse purging the compressed air? if the latter - what is the device? how exactly to do so? it is the masterpiece by LZOS (air spaced triplet).

 

Many thanks in advance!

 

collimating.jpg

 

 

Best,

Andrey



#2 Kunama

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Posted 21 October 2019 - 08:26 PM

Dear fellow astronomers,

 

May I have quite a newbie question?

 

My main caliber has got some dust on the inner side of the objective recently (do not ask) and recently has got new focuser. it seems that I will have to remove the lens cell, clean it and when assemble back. so the scope surely will lose its collimation. Previously, I have not performed such an art. So, here are my questions:

 

1. What tools exactly do I need to have to collimate my refractor?  I have read a couple of CN topics re collimating refractors, including "adventures in Refractor Collimation", so I have a feeling that I have high level understanding (in general) of the steps to undertake. But what would be the best options for the tools? Reasonably priced - not sure if I want to go such great instruments as Howie Glatter mostly due to its high prices - for me it is (hopefully) going to be one time procedure, so do not want to expense a lot of funds, unless, you advise against this approach.

1.1. Laser collimator to ensure that focuser is aligned.  Which exactly?

1.2. Cheshire collimating tool, to fine tune the objective. Which exactly?

1.3 something else?

Or it is not a good idea for a newbie to explore this route and better to seek for help at local astronomy association experts?

 

2. Also, how do you remove the dust in between of the lenses in the cell? I am not going to disassemble the cell, but since the dust somehow appeared there - perhaps it is possible to remove? vacuuming or vice verse purging the compressed air? if the latter - what is the device? how exactly to do so? it is the masterpiece by LZOS (air spaced triplet).

 

Many thanks in advance!

 

attachicon.gif collimating.jpg

 

 

Best,

Andrey

Andrey, 

I have just been through this today, it all depends on which model, which cell  etc.

With the TMB-LZOS 152 the cell unscrews from the countercell that allows you to clean the front of G1 and rear of G3 element.  There is no way for getting into the cell to do any other cleaning without disturbing not only the collimation of the cell but also the alignment of the lenses.  Are you sure the dust is within the lens elements?

 

I checked the collimation today before and after cell removal and saw no change.

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#3 dron2015

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Posted 21 October 2019 - 08:45 PM

Dear Matt,

 

Thanks much! Mine ilooks the same with S/N quite close to that of you lens! smile.gif

 

However, I do not see the pull and push screws on yours.. I see the thread on yours! hmmm perhaps mine is a bit different in the cell structure.

 

i thought that I saw small holes in the cell sealed with smthng white - to let the air move in and out and no dew accumulates, will have a look again!

 

Best,

Andrey


Edited by dron2015, 21 October 2019 - 09:12 PM.


#4 Jeff B

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Posted 21 October 2019 - 08:48 PM

You have the right tools in mind but like Matt said, leave the inner dust alone.  Also being a newbie, shining a bright light into the objective and viewing off axis WILL show some debris so I have to ask, how "bad" is it?  A few specks?  Even a couple of dozen specs, while annoying, will not affect the performance of the lens. 

 

Regarding the laser to use, just make sure that when you put the laser snugly in the eyepiece holder, shine it on a wall and then rotate the laser, the beam on the wall stays put and does not "orbit".  If it does, the laser itself is not collimated.  Get one that is.  Also what scope is it and does it have lens cell and focuser collimation features?

 

Jeff


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#5 Jeff B

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Posted 21 October 2019 - 08:50 PM

Dear Matt,

 

Thanks much! Mine ilooks the same with S/N quite close to that of you lens! smile.gif

 

However, I do not see the pull and push screws on yours.. hmmm perhaps mine is a bit different in the cell structure.

 

i thought that I saw small holes in the cell sealed with smthng white - to let the air move in and out and no dew accumulates, will have a look again!

 

Best,

Andrey

Leave those alone!!!

 

Those are the radial screws that center the lens elements!!

 

Jeff


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#6 dron2015

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Posted 21 October 2019 - 08:51 PM

Thanks much, Jeff!

 

the inner part has some than a couple of dozens frown.gif

 

regarding the “small holes” - thanks much Jeff for warning!

 

Best,

Andrey


Edited by dron2015, 21 October 2019 - 08:52 PM.


#7 Jeff B

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Posted 21 October 2019 - 08:58 PM

Thanks much, Jeff!

 

the inner part has some than a couple of dozens frown.gif

 

Best,

Andrey

That's too bad. 

 

If you are in the EU contact Markus Ludes at APM for service.  Well, even if you are not in the EU, contact him.  There will a good sized fee but he's a good guy, will do a good job for you and if it is a 152mm F7.9 LZOS triplet, the charge will be well worth it..  I have had several APM/TMB LZOS triplets and they were all truly excellent lenses.  

 

Jeff


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#8 dron2015

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Posted 23 November 2019 - 03:00 AM

Fellows,

 

This is one of mine refractors. Howie Glatter is in the focuser. Rotating laser  the dot does not move. The paper attached directly to the lens cells. Looks symmetrical attachment to me.

 

Should I deliberate the process of not underestimating the importance of beginning   to move forward to the conceptualization of starting to worry?

 

Thanks!

 

Best,

Andrey

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#9 John Huntley

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Posted 23 November 2019 - 06:42 AM

Looks like the optical axis of the focuser is not quite aligned with the optical axis of the objective. The adjustment needed is to tilt the focuser slightly to get the laser dot centred.


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#10 dron2015

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Posted 27 November 2019 - 10:18 PM

Well, I am getting better at the refractor collimation!

Now - star test is to be performed and (hopefully) pass!

Best,

Andrey

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#11 Steve Allison

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Posted 28 November 2019 - 12:18 PM

Perfection!


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#12 syxbach

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Posted 29 November 2019 - 01:50 PM

Andrey

 

How did you do that? Any tips? Thank you 

 

Yuexiao

Well, I am getting better at the refractor collimation!

Now - star test is to be performed and (hopefully) pass!

Best,

Andrey



#13 Jeff B

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Posted 29 November 2019 - 02:31 PM

Andrey

 

How did you do that? Any tips? Thank you 

 

Yuexiao

Depends on the focuser and how it is attached to the end of the main tube. 

 

If the focuser is attached to the end of the main tube with screws, those can be loosened slightly and the focuser nudged to line up the laser with the center.  You then carefully tighten the screws while watching the laser dot.  If the stock screws are counter-sunk, replace them with regular screws and washers.  

 

The larger diameter Feather Touch focusers have three small alignment screws in their end caps which can be used to align the focuser as well as lock the end cap in place so it will not auto-rotate.

 

Jeff 


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#14 dron2015

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Posted 29 November 2019 - 03:46 PM

Yuexiao,

 

First of all, most probably you do not need to do anything of that. Nowadays, refractors are being manufactured very well, and producers align and collimate everything. and refractors are well known for keeping collimation vey well.

 

Also note - that I am not yet a grandmaster of collimation - so take all my advice with a grain of salt.

 

In my particular case - I have quite old refractor on which I decided to change focuser (Moonlite - I really like Ron's products!). do to the age of the scope this change happened not without 'tricks" so it was quite a must for me to check the collimation.

 

First step of any collimation process is to check if optical axis of focuser and that of the lens are aligned.  To do this test you need a laser.  On my first picture  the axes are not aligned, on the second they do. How did I do that? this sort of alignment should be done at the side of focuser (not the lens!). it depends on the focuser. I knew that my focuser is new and collimated (it can rotate so it required manufacturer's collimation. when it rotates - it should always point the laser to the same place.) - so I avoided change position of collimation screws of the focuser and  added collimation plate between the scope and my new focuser   - it  took like 20 minutes to align axes after I added this plate. If I would change positions of the screws on the focuser instead of adding the plate - It would A) break the manufacturer's collimation of the focuser 2) align focuser and lens only for one specific position of focuser rotation ring and I  rotate the focuser - the lens and focuser would become again misaligned.    After aligning focuser and lens - I did rotate my focuser several times like 360 deg and it was always the same spot on the lens - perfect!

 

Note - is all depends on the focuser - other types of focuser might be aligned differently and might not require adding collimation plate - here might be other techniques.

 

Having aligned optical axis, the second step is to check how well lens collimated - it is usually done with the help of an artificial start (or special EPs). I used so takahashi collimating refractor, which I sourced here on CN - so I could do this Lens collimation indoors. At this step, you should have perfect concentric airy disks use push and pulls screws on your lens (do not touch focuser for now). Do NOT do this step until step 1 is performed.

 

Third step would be to repeat step 1 and 2 again smile.gif

 

My next step is test thru artificial star - but it is raining frown.gif. Artificial start testing  requires outdoors - and distance like 100-150 meters .here is a book a whole book on that - Star Testing Astronomical Telescopes: A Manual for Optical Evaluation. Whatever I could do indoors I already did. Using takahashi collimating scope I am pretty much sure - my scope is collimated well (at least better than it was) but anyway - artificial star test is to be performed.

 

Ultimate step is of course test on a real star. Artificial star testing - is much easier - it can be cloudy, artificial star does not move, etc.

 

Good luck!

 

Best,

Andrey


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#15 dron2015

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Posted 11 December 2019 - 02:50 AM

It is a kind of sunny weather all the days but rainy every evening. Today, I run away from my office earlier to catch "good weather" and to do artificial star test.

 

My scope FL is 1200 mm and I used initially TV Nagler 5mm. I placed Artificial star like 60 m from the scope.  It works  very well. Did see all airy disks(do not forget - I am quite newbie)  and they are symmetrical and co-centrical! Basically the pictures were as you can see them in the books!  I was really surprised! Meaning that I collimated everything just fine. 

 

However, perhaps I  would never be able to collimate my scope with artificial star only -  every time you touch the scope or the mount the setup vibrated and it took some time to see the picture... and these push and pull screws!  I would lost my patience very soon. Tak collimating scope is much more convenient - and also you can do that indoors. But artificial star is a good test in the end of the processes.

 

Having tested w/ Nagler 5 mm, I decided to use Meade ploss 6mm (very basic one) -  guess what - rain started again - so cannot say anything :(

 

Next step would be to make a photo of all airy disks  using artificial star and EP projection technique.  

 

 

Thanks!

 

Best,

Andrey



#16 syxbach

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Posted 11 December 2019 - 05:13 PM

Thank you Andrey, really appreciate you description. My refractor has a built-in tilt adjuster at the end of the focuser. I know use is to adjust until stars are round all over the sensor. Still a little painful before my each imaging starts

 

Best

 

Yuexiao

 

 

Yuexiao,

 

First of all, most probably you do not need to do anything of that. Nowadays, refractors are being manufactured very well, and producers align and collimate everything. and refractors are well known for keeping collimation vey well.

 

Also note - that I am not yet a grandmaster of collimation - so take all my advice with a grain of salt.

 

In my particular case - I have quite old refractor on which I decided to change focuser (Moonlite - I really like Ron's products!). do to the age of the scope this change happened not without 'tricks" so it was quite a must for me to check the collimation.

 

First step of any collimation process is to check if optical axis of focuser and that of the lens are aligned.  To do this test you need a laser.  On my first picture  the axes are not aligned, on the second they do. How did I do that? this sort of alignment should be done at the side of focuser (not the lens!). it depends on the focuser. I knew that my focuser is new and collimated (it can rotate so it required manufacturer's collimation. when it rotates - it should always point the laser to the same place.) - so I avoided change position of collimation screws of the focuser and  added collimation plate between the scope and my new focuser   - it  took like 20 minutes to align axes after I added this plate. If I would change positions of the screws on the focuser instead of adding the plate - It would A) break the manufacturer's collimation of the focuser 2) align focuser and lens only for one specific position of focuser rotation ring and I  rotate the focuser - the lens and focuser would become again misaligned.    After aligning focuser and lens - I did rotate my focuser several times like 360 deg and it was always the same spot on the lens - perfect!

 

Note - is all depends on the focuser - other types of focuser might be aligned differently and might not require adding collimation plate - here might be other techniques.

 

Having aligned optical axis, the second step is to check how well lens collimated - it is usually done with the help of an artificial start (or special EPs). I used so takahashi collimating refractor, which I sourced here on CN - so I could do this Lens collimation indoors. At this step, you should have perfect concentric airy disks use push and pulls screws on your lens (do not touch focuser for now). Do NOT do this step until step 1 is performed.

 

Third step would be to repeat step 1 and 2 again smile.gif

 

My next step is test thru artificial star - but it is raining frown.gif. Artificial start testing  requires outdoors - and distance like 100-150 meters .here is a book a whole book on that - Star Testing Astronomical Telescopes: A Manual for Optical Evaluation. Whatever I could do indoors I already did. Using takahashi collimating scope I am pretty much sure - my scope is collimated well (at least better than it was) but anyway - artificial star test is to be performed.

 

Ultimate step is of course test on a real star. Artificial star testing - is much easier - it can be cloudy, artificial star does not move, etc.

 

Good luck!

 

Best,

Andrey




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