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Collimating a Newtonian

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#1 kevinbreen

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Posted 12 May 2021 - 10:17 AM

I'm new to Newtonians, having recently bought a 10" f/4, and curious as to how you collimate yours.
I use a laser collimator in the daytime and that's easy to use to get "collimated", but what then if a star appears comet-like at night? My understanding is that if the star exhibits a tail due to bad collimation, then the primary mirror should be adjusted so as to move the star tail-first out of the FOV. I've been advised that this is is way to achieve better collimation. Does this sound correct?
I haven't had a clear night yet but I'd like to get ready as best as possible for when it is clear.

Any pointers would be much appreciated.

Kev

#2 f300v10

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Posted 12 May 2021 - 10:49 AM

There are numerous threads on collimation in the Equipment/Reflectors forum.  You would also likely get more responses to any questions if they were posted to that forum. 

 

I recently started using a 12" F4 Newt myself for DSO astrophotography.  I found using a barlow/laser an excellent way to achieve very accurate collimation in the field at night.  Here is an excellent video explaining this method:

 

https://www.youtube....h?v=ZCAy0kYnk9g


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#3 spereira

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Posted 12 May 2021 - 11:11 AM

Moving to Reflectors.

 

smp



#4 schai

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Posted 12 May 2021 - 11:25 AM

This is a pot of stew with wayyyyy too much meat and stuff.

lot of nutrition but no clarity

 

the short answer is find a mentor locally who can show you the ropes.

 

the long answer would go for pages and pages

 

my first comment would be to move the star in question around your field of view. See how the shape changes as it goes from central to peripheral and how asymm it is and directionality

mindful what power you are using.

report back and see the myriad responses

 

my second comment is search and read the web

Howie glatter does a decent job regarding laser collimation

Once you grasp the basics start to get your head around the limitations of laser collimation

catseye goes into a lot mor depth 

you enter the realm of amateur expert once you read suiter’s star testing astronomical telescopes

 

if you dare, wade into the myriad posts in the reflector forum on this topic



#5 Starman1

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Posted 12 May 2021 - 02:18 PM

This thread is pretty much all you need.  Even the first post is sufficient.

https://www.cloudyni...your-newtonian/



#6 Jeff Morgan

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Posted 13 May 2021 - 12:24 AM

Vic Menard's New Perspectives in Newtonian Collimation will be the best money a Newtonian owner can spend.

 

And it is only about $20.


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#7 B 26354

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Posted 13 May 2021 - 12:33 AM

Vic Menard's New Perspectives in Newtonian Collimation will be the best money a Newtonian owner can spend.

 

And it is only about $20.

https://www.catseyec...rspectives.html


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#8 CHASLX200

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Posted 13 May 2021 - 05:43 AM

Stars will still look like a comet at the field edge thanks to coma at F/4.  Hope you have a Paracorr.


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#9 kevinbreen

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Posted 13 May 2021 - 05:52 AM

Stars will still look like a comet at the field edge thanks to coma at F/4. Hope you have a Paracorr.


Indeed I do

#10 kevinbreen

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Posted 13 May 2021 - 05:52 AM

Thanks very much for all the help, folks

#11 eastwd

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Posted 13 May 2021 - 06:08 AM

I have a custom, equatorially mounted 375mm f/6 Newtonian John Pratte made for me that I use for planetary and lunar imaging. Precise collimation is hugely important when using a Newt for planetary imaging, and I typically recollimate multiple times a night, including anytime I slew the scope any meaningful distance at all. If it fits your budget, you can’t do better than the Catseye “2” Deluxe Triplepack XLKP Set:”

 

http://www.catseyecollimation.com/
 

It’s a joy to use. There are videos on YouTube that make using it a breeze, even on your first night out. This one is particularly helpful:

https://m.youtube.co...h?v=Vj12cx3tnsM

 

At roughly $400, it’s pricey — kind of the Rolls-Royce of collimation tools. But it makes achieving precise collimation lightning fast and easy. The component in the set that’s most useful for achieving critical collimation is the “INFINITY XLKP 2-pupil Autocollimator.”  The set comes with the Menard book included, but the tools and videos make the process so easy that you won’t really need to read it. I also have a Glatter laser collimator and TuBLUG, which is great for aligning the primary mirror on Newts whose tubes are too long to allow you to reach the primary mirror collimation knobs while looking through the focuser. But the Catseye XLKP set takes the process to another level entirely. I hope this helps.

 

Larry


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#12 CHASLX200

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Posted 13 May 2021 - 06:16 AM

The faster the optics the more picky you gotta be about collimation. Just a little bit off with my 18" F4.5 will really show up in a image of a planet. I have super steady seeing and only view planets at higher powers. I use Tectron tools.  My laser is off and will need to buy another 1.


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#13 MellonLake

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Posted 13 May 2021 - 07:52 AM

I'm new to Newtonians, having recently bought a 10" f/4, and curious as to how you collimate yours.
I use a laser collimator in the daytime and that's easy to use to get "collimated", but what then if a star appears comet-like at night? My understanding is that if the star exhibits a tail due to bad collimation, then the primary mirror should be adjusted so as to move the star tail-first out of the FOV. I've been advised that this is is way to achieve better collimation. Does this sound correct?
I haven't had a clear night yet but I'd like to get ready as best as possible for when it is clear.

Any pointers would be much appreciated.

Kev

Collimation is 3 steps:

 

1) Centre and round the secondary under the focuser.  This is best done with a sight tube or combo tool (Astrosystems Lightpipe[short] or Telecat)

2) Align the secondary. This is best done with a thin beam laser (your laser may be acceptable provided it is well aligned).  I prefer the Farpoint laser.

3) Align the primary mirror.  This is best done with a Calibrated Cheshire like the Farpoint or Catseye.   I would not recommend using a laser with a target for this step (which it sounds like you have) as these are not particularly accurate for aligning the primary mirror.  

 

These steps must be done in order.  Steps #2 and #3 should be done every time you set up the telescope (i.e. outside just before you start using it).  Step #1 rarely needs to be done but should be periodically checked.  Each time I use my telescope I check the collimation with a star test just to be sure it is right. 

 

As your telescope is F/4, step #3 is particularly critical.  If you get a coma corrector, which would be nice for an F/4 telescope, step #2 becomes critical as well.  

 

Rob


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#14 happylimpet

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Posted 13 May 2021 - 02:50 PM

Collimation is 3 steps:

 

1) Centre and round the secondary under the focuser.  This is best done with a sight tube or combo tool (Astrosystems Lightpipe[short] or Telecat)

2) Align the secondary. This is best done with a thin beam laser (your laser may be acceptable provided it is well aligned).  I prefer the Farpoint laser.

3) Align the primary mirror.  This is best done with a Calibrated Cheshire like the Farpoint or Catseye.   I would not recommend using a laser with a target for this step (which it sounds like you have) as these are not particularly accurate for aligning the primary mirror.  

 

These steps must be done in order.  Steps #2 and #3 should be done every time you set up the telescope (i.e. outside just before you start using it).  Step #1 rarely needs to be done but should be periodically checked.  Each time I use my telescope I check the collimation with a star test just to be sure it is right. 

 

As your telescope is F/4, step #3 is particularly critical.  If you get a coma corrector, which would be nice for an F/4 telescope, step #2 becomes critical as well.  

 

Rob

Yeah agree with the above though i think for #3 a barlowed laser (assuming primary is centre spotted, and accurately!) will do a fine job.

 

And regardless of anything, I would finish with a star test, and use the 'move stars tail first out of the FOV' method!!! Mustve been a certified smart-**** told you that one.



#15 MellonLake

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Posted 13 May 2021 - 03:00 PM

Yeah agree with the above though i think for #3 a barlowed laser (assuming primary is centre spotted, and accurately!) will do a fine job.

 

And regardless of anything, I would finish with a star test, and use the 'move stars tail first out of the FOV' method!!! Mustve been a certified smart-**** told you that one.

The calibrated Cheshire is more accurate than the Barlowed Laser. The shadow of the mirror marker on the Tublug target (Or Blug or similar) is a little more difficult to centre.  With and F/4 and the accuracy required for the primary alignment, I would personally prefer the Cheshire.   Also, if you are using the Barlowed laser with a "cheap Targeted Laser" this technique is far less accurate than the Tublug, Blug or similar methods where the beam does not come back through the Barlow.  I have built and designed many Collimation devices and a good Calibrated Cheshire, where you centre the mirror marker in the ring of the Cheshire (like Farpoint or Catseye) is more accurate. 

 

(I have 3D printed many collimation devices and developed two new ones of my own design). 

 

Rob   


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#16 Starman1

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Posted 13 May 2021 - 05:14 PM

The calibrated Cheshire is more accurate than the Barlowed Laser. The shadow of the mirror marker on the Tublug target (Or Blug or similar) is a little more difficult to centre.  With and F/4 and the accuracy required for the primary alignment, I would personally prefer the Cheshire.   Also, if you are using the Barlowed laser with a "cheap Targeted Laser" this technique is far less accurate than the Tublug, Blug or similar methods where the beam does not come back through the Barlow.  I have built and designed many Collimation devices and a good Calibrated Cheshire, where you centre the mirror marker in the ring of the Cheshire (like Farpoint or Catseye) is more accurate. 

 

(I have 3D printed many collimation devices and developed two new ones of my own design). 

 

Rob   

I tend to agree.

I can see a deviation of 1/100 the diameter of the center marker in a calibrated Cheshire, where it is hard to be that accurate with a center mark shadow in a Barlowed laser setting.

However, if the Barlowed laser surface is itself calibrated, like the Howie Glatter Tublug, there is an incredibly thin ring of red light inside the center mark shadow but outside the hole in the Barlow screen.

That thin ring of red is easy to make completely uniform in thickness, and that degree of accuracy is the same as a calibrated Cheshire.

After all, the error we see is actually 2X the error in the mirror alignment.

 

I prefer the Cheshire, but then I always do my final collimation shortly after sunset when everything is highly visible, finishing off with an accurate first-surface autocollimator and Cheshire repetition.

If one collimates in complete darkness, a barlowed laser is normally where one stops.  An autocollimator  used in the dark requires a special red light that illuminates the center marker strongly enough to see all the reflections, as does a Cheshire.



#17 CHASLX200

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Posted 13 May 2021 - 06:16 PM

I tend to agree.

I can see a deviation of 1/100 the diameter of the center marker in a calibrated Cheshire, where it is hard to be that accurate with a center mark shadow in a Barlowed laser setting.

However, if the Barlowed laser surface is itself calibrated, like the Howie Glatter Tublug, there is an incredibly thin ring of red light inside the center mark shadow but outside the hole in the Barlow screen.

That thin ring of red is easy to make completely uniform in thickness, and that degree of accuracy is the same as a calibrated Cheshire.

After all, the error we see is actually 2X the error in the mirror alignment.

 

I prefer the Cheshire, but then I always do my final collimation shortly after sunset when everything is highly visible, finishing off with an accurate first-surface autocollimator and Cheshire repetition.

If one collimates in complete darkness, a barlowed laser is normally where one stops.  An autocollimator  used in the dark requires a special red light that illuminates the center marker strongly enough to see all the reflections, as does a Cheshire.

Every time i roll my 18" Dob out i need to touch up collimate, Hard to do at nite with my Tectron Cheshire. But i use a flash light and get enough light for it to work pretty good.  Most times i roll out before sundown and have not trouble in the day light. But now that the planets are up around 5 am it is a pain without a laser.  My laser was shot and way off.



#18 kevinbreen

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Posted 14 May 2021 - 05:35 AM

Yeah agree with the above though i think for #3 a barlowed laser (assuming primary is centre spotted, and accurately!) will do a fine job.

And regardless of anything, I would finish with a star test, and use the 'move stars tail first out of the FOV' method!!! Mustve been a certified smart-**** told you that one.


Ha ha. Yes, it was a contented mollusc alright


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