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Laser collimation for Newtonian

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#1 gfunkernaught

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Posted 03 August 2020 - 09:50 PM

I recently purchased the Meade Laser Collimator and I am trying to collimate my Meade 4" Newtonian.  I followed the instructions but I am having an issue getting a red dot.  I instead see a larger red dot.  When I point the laser at the wall I get a small dot.  I also made sure the laser itself is collimated by rotating the device in place and watching the dot, it did not make a circle, it stayed in place.  When I look at the window with the target or bullseye, I see a large red dot not the small dot.  I can see the small dot only when I tilt the device.  To test I held the device tilted and watched the small dot as I adjusted the collimation screws of the primary mirror, the dot did not move at all.  If I put the device all the way down into the focuser, secure it with the eyepiece screws then adjust the primary mirror, I can see the large red dot move but it covers the whole target so I cannot tell if it is centered.  Please see the attached pictures and advise. I don't know what I am doing wrong.  I noticed that there is a lens inside the focuser so I am thinking that could be magnifying the red dot.  Could someone help me out?

Attached Thumbnails

  • IMG_20200803_223625.jpg
  • IMG_20200803_223718.jpg
  • IMG_20200803_223742.jpg


#2 N3p

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Posted 03 August 2020 - 10:04 PM

Buy a Cheshire sight tube instead.. to learn how to do it.

https://agenaastro.c...reflectors.html

 

Read this

http://www.astro-bab...nian-reflector/

 

Others will help you with the laser.


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#3 Cames

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Posted 03 August 2020 - 10:46 PM

Look into the focuser tube in the photo you posted. See that there is a corrector lens present inside the focuser tube?  That lens has a diffusing effect on the laser beam similar to what we see when lasers shine through Barlow lenses.  It converts the coherent beam to one that is spread out like a flashlight. 

 

Telescopes with the built-in corrector like the one in the photo require unique collimation procedures.  Conventional collimation tools whether they be lasers or combination Cheshires are not designed for that type of telescope.

 

I have heard of cases where the lens can be unscrewed from the focuser so that there is an unobstructed path to the secondary mirror.  The laser will then operate as it does in conventional Newtonian design telescopes. Conventional Newtonians don't have that corrector lens in the optical train.  Once the OTA is collimated, the corrector lens is screwed back into the focuser tube.

-------------

C

 

I don't recommend unscrewing the corrector unless you are experienced.  It's possible to invert or incorrectly reassemble the compound corrector lens and then you will have a problem you can't fix.

 

Search for instructions on "Collimating a Bird-Jones Telescope"


Edited by Cames, 03 August 2020 - 11:09 PM.

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#4 gfunkernaught

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Posted 03 August 2020 - 11:19 PM

Look into the focuser tube in the photo you posted. See that there is a corrector lens present inside the focuser tube?  That lens has a diffusing effect on the laser beam similar to what we see when lasers shine through Barlow lenses.  It converts the coherent beam to one that is spread out like a flashlight. 

 

Telescopes with the built-in corrector like the one in the photo require unique collimation procedures.  Conventional collimation tools whether they be lasers or combination Cheshires are not designed for that type of telescope.

 

I have heard of cases where the lens can be unscrewed from the focuser so that there is an unobstructed path to the secondary mirror.  The laser will then operate as it does in conventional Newtonian design telescopes. Conventional Newtonians don't have that corrector lens in the optical train.  Once the OTA is collimated, the corrector lens is screwed back into the focuser tube.

-------------

C

 

I don't recommend unscrewing the corrector unless you are experienced.  It's possible to invert or incorrectly reassemble the compound corrector lens and then you will have a problem you can't fix.

 

Search for instructions on "Collimating a Bird-Jones Telescope"

Ah-ha!  The rabbit hole deepens....I figured that lens was causing the problem.  I just watched the first result that came up on google "Collimating a bird-jones telescope" and voila taking the lens out its extremely simple.  I will try this out.  Thanks for the info!



#5 JohnBear

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Posted 03 August 2020 - 11:28 PM

THis is what we call a "Bird-Jones" reflector design which unfortunately is used on mass produced to keep the costs to a minimum. That likely means that you also do not spherical mirror rather that the preferred parabolic mirror. 

 

It still could be a very usable beginner telescope to see planets and larger objects, but not at the best resolutions and higher magnifications. As you noted, there are a few ways to collimate bird-jones scopes, so do the best you can - then take it out and get some use out of it!  You will learn and eventually know more about what scope you want need for an upgrade. 

 

Also join a local astronomy club to really speed up the learning process and also learn about the wide variety of telescope you may want to go for next.

 

Best of luck and clear skies!



#6 gfunkernaught

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Posted 03 August 2020 - 11:46 PM

So it looks like the ring that holds the lens in is glued.  I can see the two small notches in the ring that hold the lens inside the tube (like in the video) but there is visible glue coming out of the sides, where the ring and tube meet.  I tried to turn it the way it was shown in this video https://www.youtube....?v=5yLJh31bWNQ  but it won't budge.  Honestly I have thought about replacing this focuser with a better one.  I've been using this scope for visual to have something to do while my SCT does my imaging.  The newt is actually pretty good.  Was able to see Andromeda clearly after about 2-3 hours of acclimation at a dark site.  I rather spend a little on this scope than buy a whole new scope just for visual.  



#7 JohnBear

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Posted 04 August 2020 - 12:33 AM

If you don't have one, you can read up on how to put a "center dot" on your primary mirror. Then read about the "barlowed laser" method of collimation. Since your scope already has the balow in the focuser, that should work reasonably well on a Bird-Jone scope. I have done it on two B-J scopes myself.



#8 Cames

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Posted 04 August 2020 - 04:48 AM

[snip]

 

Honestly I have thought about replacing this focuser with a better one.

 

 [snip]

The corrector lens is important for that telescope to perform satisfactorily.  If the performance of that telescope is to be preserved, replacing the focuser will be complicated and, I presume, very expensive. A better option might be a modified, two-stage collimation without modifying the telescope. 

 

Stage 1

  • Perfect the tilt of the secondary mirror inside, using the dispersed laser dot.  The broad dot should end up centered on the primary mirror when viewed from the front aperture.  Hold a sheet of paper over the aperture before peeking into the telescope in order to see the dot. You don't want the laser beam to hit you in the eyes.

 

Stage 2

  • Perfect the tilt of the primary mirror outside at night using Polaris.  Has to be at night, so you can see Polaris but your work area must be comfortably lit. Stage 2 takes a monumental amount of patience.  Get Polaris into the center of the field of view of a high power eyepiece.  Defocus Polaris a little just until you see the bullseye rings appear.  If the bullseye rings appear symmetrical while Polaris stays in the center of the field of view, you are done! 
  • If not, you must tilt the primary until you achieve centering and symmetry simultaneously.  I would make careful notes, as you work, about which screw does what effect on the symmetry.  Every time you twist a screw, you will need to re-center Polaris before evaluating bullseye symmetry.  Probably best done over two moonlit nights. Manipulating the push-pull collimating screws in order to achieve pure tilt without binding is a learning experience in itself and must be mastered whichever collimation method or tool you use.

Patience and organization in abundance will eventually get you there.

------------

C



#9 gfunkernaught

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Posted 04 August 2020 - 08:33 AM

If you don't have one, you can read up on how to put a "center dot" on your primary mirror. Then read about the "barlowed laser" method of collimation. Since your scope already has the balow in the focuser, that should work reasonably well on a Bird-Jone scope. I have done it on two B-J scopes myself.


I have looked it up and while it doesn't look crazy hard it does seem tedious. So would putting a center dot on the primary mirror cause a "shadow" to appear on the bullseye of the laser collimator? I'm thinking that would block the light indicating the center of the mirror.

#10 gfunkernaught

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Posted 04 August 2020 - 08:37 AM

The corrector lens is important for that telescope to perform satisfactorily. If the performance of that telescope is to be preserved, replacing the focuser will be complicated and, I presume, very expensive. A better option might be a modified, two-stage collimation without modifying the telescope.

Stage 1

  • Perfect the tilt of the secondary mirror inside, using the dispersed laser dot. The broad dot should end up centered on the primary mirror when viewed from the front aperture. Hold a sheet of paper over the aperture before peeking into the telescope in order to see the dot. You don't want the laser beam to hit you in the eyes.

Stage 2
  • Perfect the tilt of the primary mirror outside at night using Polaris. Has to be at night, so you can see Polaris but your work area must be comfortably lit. Stage 2 takes a monumental amount of patience. Get Polaris into the center of the field of view of a high power eyepiece. Defocus Polaris a little just until you see the bullseye rings appear. If the bullseye rings appear symmetrical while Polaris stays in the center of the field of view, you are done!
  • If not, you must tilt the primary until you achieve centering and symmetry simultaneously. I would make careful notes, as you work, about which screw does what effect on the symmetry. Every time you twist a screw, you will need to re-center Polaris before evaluating bullseye symmetry. Probably best done over two moonlit nights. Manipulating the push-pull collimating screws in order to achieve pure tilt without binding is a learning experience in itself and must be mastered whichever collimation method or tool you use.
Patience and organization in abundance will eventually get you there.
------------
C

I've learned how to adjust the primary mirror even indoors. I used a bright surface too illuminate the primary mirror and see the "spider" shadow of the objective that is off center. I can see it move while I adjust the screws. Although I centered it just by looking at it through the eyepiece hole, when I put the laser on, it doesn't seem centered. If I took the Focuser tube out completely, and managed to keep the laser collimator secured and centered within the open hole, would that work?

#11 JohnBear

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Posted 04 August 2020 - 10:42 AM

 

Patience and organization in abundance will eventually get you there.

That is true - EVENTUALLY!

You seem to be pretty much flying blind here. A lot of newbies fall into the experimental collimation trap - so you are not alone.  That usually results in a massively misaligned telescope in addition to a severely frustrated owner - not to mention missing weeks of enjoying really good views of the planets this time of year while the telescope is unusable. 

 

Your best course of action (IMHO) - if you want to use your telescope sometime this summer - is going to be finding a nearby experienced Newt owner and have them collimate it for you (a matter of minutes), or teach/show you how to do it (maybe an hour).  Find someone from your local astronomy club today and you'll be out tonight marvelling at the planets and stars. Otherwise, it may take a while (weeks), even with all the good advice from the forum.  Just sayin',


Edited by JohnBear, 04 August 2020 - 10:46 AM.


#12 Starman1

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Posted 04 August 2020 - 06:09 PM

So it looks like the ring that holds the lens in is glued.  I can see the two small notches in the ring that hold the lens inside the tube (like in the video) but there is visible glue coming out of the sides, where the ring and tube meet.  I tried to turn it the way it was shown in this video https://www.youtube....?v=5yLJh31bWNQ  but it won't budge.  Honestly I have thought about replacing this focuser with a better one.  I've been using this scope for visual to have something to do while my SCT does my imaging.  The newt is actually pretty good.  Was able to see Andromeda clearly after about 2-3 hours of acclimation at a dark site.  I rather spend a little on this scope than buy a whole new scope just for visual.  

The scope will not work without that lens.  Do not change the focuser.

There is a way to collimate it, but it is complicated and requires partially dismantling the scope to do so.

I would suggest you leave the secondary mirror alone and collimate the scope on a star, which is a primary mirror-only procedure.

These are good instructions:

https://garyseronik....pe-collimation/


Edited by Starman1, 04 August 2020 - 06:10 PM.


#13 Starman1

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Posted 04 August 2020 - 06:13 PM

I have looked it up and while it doesn't look crazy hard it does seem tedious. So would putting a center dot on the primary mirror cause a "shadow" to appear on the bullseye of the laser collimator? I'm thinking that would block the light indicating the center of the mirror.

You put a white paper cover on the bottom of the focuser.  That white paper has a center hole in it about 1/8" in diameter.

The laser goes through the hole in the paper and is defocused enough to cover the center marker on the primary mirror.

The shadow of the center marker is returned to the white paper on the focuser and you adjust the primary to center the shadow on the hole in the paper.

You do not have the laser pass back through the lens a 2nd time.

 

However, there is no reason to go to such lengths when the star collimation technique I posted in my last post will get you there without tools.


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#14 gfunkernaught

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Posted 05 August 2020 - 01:21 PM

Well we got hit by the storm, tree down and no power. my portable power station is being reserved so I won't be going out for a bit. I will ask around my local community to see if someone can actually show me how to do it. But just hashing out ideas here. If I took a piece of paper and put a small hole through it, then used the laser collimator, would that shrink the dot down to be more accurate? I can actually tell if it is centered just from looking at the primary mirror from the objective.

#15 JohnBear

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Posted 05 August 2020 - 02:41 PM

OK, I went ahead and googled "barlowed laser collimation" for you. Google is your friend when you don't know something and want to learn. 

 

This is about as simple as you will find it - with pictures

https://www.obsessio...ation/index.php

 

(Although they seem to prefer a very expensive TeleVue's big barlow, this will also work on a Bird-Jones with a cheap laser.)

Good luck.



#16 gfunkernaught

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Posted 12 August 2020 - 09:01 PM

OK, I went ahead and googled "barlowed laser collimation" for you. Google is your friend when you don't know something and want to learn. 

 

This is about as simple as you will find it - with pictures

https://www.obsessio...ation/index.php

 

(Although they seem to prefer a very expensive TeleVue's big barlow, this will also work on a Bird-Jones with a cheap laser.)

Good luck.

I actually did that first, and found many results for collimation for newts that dont have a barlow inside the focuser.  I know how to google smile.gif .  I didn't know about Bird-Jones until it was mentioned here.  So the technique you linked was kind of mentioned here already.  I was thinking of just taking a piece of hard paper and putting a perfect circle hole in the middle to make the red dot of the laser more narrow to make things easier.  Just got my power back from the storm and I am totally shot from collecting firewood.


Edited by gfunkernaught, 12 August 2020 - 09:01 PM.


#17 gfunkernaught

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Posted 15 August 2020 - 01:32 PM

So I just manually collimated the scope as per the manual lol.  Did it indoors with a bright yellow square piece of packing foam in front of the objective and its a lot better than before.  Didn't use any paper with holes in it or anything.  Just a screwdriver and alan key.




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