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Equipment Discussions >> Reflectors

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Jason D
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Re: How to Collimate your Newtonian new [Re: nheacock]
      #4535477 - 04/21/11 10:10 PM

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4531553/page/0/view/collapsed/sb/5/o/all/fpart/1

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Tesselator
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Reged: 07/16/10

Loc: Japan
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4639237 - 06/14/11 08:02 PM

Quote:

I've already posted my "procedure" before, but I'll be happy to do it again.




Thanks! I recently investigated collimation myself too. I recently added a Vixen Super Polaris R-130-S to my scope collection (of 2 ). This is my first reflector. It's a Newtonian telescope... what a neat names you cosmologists come up with. I almost feel like in owning one of these I'll now be able to command gravity or something. I guess I got a good deal on it (??) $50 for the scope, 3 eyepieces, a motor driven mount that seems to weigh several tons, and some fairly sturdy legs. Anyway, being me, I had to find out everything I could about it and found out that these types of scopes occasionally need to be Collimated. Not having any idea what Collimation was nor what skills and tools were involved I began searching. After reading just about every tutorial and watching just about every video I finally came across a guy making a little sense! Yay for making sense!!! So here's a playlist and the nine parts!

Playlist: YouTube - Broadcast Yourself.


Embeded videos:

Part 1:
YouTube - ‪Newtonian Collimation Part 1‬‏

Part 2:
YouTube - ‪Newtonian Collimation Part 2‬‏

Part 3:
YouTube - ‪Newtonian Collimation Part 3‬‏

Part 4:
YouTube - ‪Newtonian Collimation Part 4‬‏

Part 5:
YouTube - ‪Newtonian Collimation Part 5‬‏

Part 6:
YouTube - ‪Newtonian Collimation Part 6‬‏

Part 7:
YouTube - ‪Newtonian Collimation Part 7‬‏

Part 8:
YouTube - ‪Newtonian Collimation Part 8‬‏

Part 9:
YouTube - ‪Newtonian Collimation Part 9‬‏



Whew! Well worth the watch tho however you choose to view it - either automatically in series at the playlist link or by clicking on the individual parts.


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Jason D
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Re: How to Collimate your Newtonian new [Re: Tesselator]
      #4639486 - 06/14/11 10:46 PM

Sorry, but that is NOT the best collimation series out there.
9 videos and the guy does not even cover how to align the focuser axis by redirecting the laser beam to the primary center. In fact, he talks against it. This guy does not understand collimation well. He is mixing focuser axial alignment with secondary mirror positioning. These are different alignments but he thinks they are the same. Interestingly, he has Vic's book as shown in the video. Maybe he should spend little more time reading that book to improve his understanding of the collimation theory.
Furthermore, he collimates the primary while the OTA is in a horizontal position -- not a good idea.
Jason


Edited by Jason D (06/15/11 12:46 AM)


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Twilight
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Reged: 06/03/10

Loc: Englewood Tennessee
Re: How to Collimate your Newtonian new [Re: Jason D]
      #4639661 - 06/15/11 01:53 AM

I would love to see Vic Menard, Jim Fly and Howie Glatter put together a video on CD for sale for about 20.00 to 25.00 bucks with the complete procedure like in Vic's book. I don't know if it could be done for 25.00 but it sure would get my buy after reading Vic's book. The video would be worth lets say 2500 words. Come on guy's I know you can do it. It would be a best seller for astronomy! Let me see here. $25.00 times 100,000 copy's. That would be a good starting point.

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Tiebreaker
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Reged: 10/12/09

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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4790735 - 09/05/11 04:09 PM

Hello All,

I refer back to the very last sentence of Vic's original post that "All tools should agree". Therein lies my problem. I've had my new Orion XT10g goto Dob for a little less than two months and have been very happy with the performance so far. But this is my first experience with a reflector and so am concerned that I can and do collimate the scope well, which I've read is especially important in a fast f4.7 scope. When I first got the scope, I used the included collimation cap and after reading the instruction manual carefully, achieved what I consider to be good collimation verified by a star test at first light. Maybe I should've left well enough alone but being obsessed with collimation, I bought a good quality laser collimator, the kind with a side window for ease of collimating from the primary end. I do recall when I first used the laser collimator, it seemed like I had to do quite a bit of adjustment from what I had achieved just using the collimation cap. I just chalked it up to that the original collimation was off from moving the scope in and out of the house several times. Then I learned about barlowed collimation for the primary and have been using that technique before each of the past two to three observing sessions. Again star tests seem to indicate that the scope was in good collimation.

But then just today (told you I was obsessed ) I decided to check the collimation. I put in the collimation cap, which I hadn't used since the first couple of collimations and much to my surprise, the collimation seemed to be significantly off. It appeared that the secondary was centered well but the primary was not very centered in the secondary (in fact, one of the four mirror retaining clips wasn't even visible) plus the primary center donut was off center as well. So I went ahead and re-collimated (first secondary then primary mirrors) using the collimation cap then inserted the laser collimater in the focuser and saw that it was out of collimation - the laser was about a quarter to half an inch off of the primary center donut and the return laser was off center on the side window to about the first concentric circle from the center spot. I went through collimation again by centering the laser on the primary center donut, put in the barlow and centering the donut shadow in the side window.

Well if you haven't been too bored and have read this far, you can guess what happened next. I removed all the laser and barlow stuff and put the collimation cap back in and again the collimation was well off. Frustrating to say the least. I've read elsewhere about laser collimators being out of collimation so I clamped a wood quarter round piece of molding in a workbench, put the laser collimator in it and slowly turned the laser while watching the laser on a white wall about six feet away. The point seemed to pretty much stay in one spot.

Star testing under both collimation techniques produce good results but how could the two techniques be so far off from each other? Any idea what I'm doing wrong??


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Vic Menard
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Reged: 07/21/04

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Re: How to Collimate your Newtonian new [Re: Tiebreaker]
      #4790847 - 09/05/11 05:05 PM

Let's start with "star testing". To precisely verify the primary mirror axial alignment on a star, you'll need to keep the star carefully centered and use a magnification of about 250X or more, defocusing the star just enough so you can see a few diffraction rings (if you can see the silhouette of the spider in the defocused star, you've defocused too much). Assuming the primary mirror center spot is well placed on the primary mirror surface, the Barlowed laser and/or the collimation cap should deliver a good star test. You can verify both of these primary mirror alignment tools by simply rotating them in the focuser drawtube--resecuring the locking screw each time before you read the alignment. Both tools should easily reveal errors in the alignment read as small as 0.02-inch, and since both tools magnify the actual primary mirror axial error 2X, you should be able to correct the primary mirror axial error to a precision of 0.01-inch.

The unBarlowed thin beam laser is useful when aligning the focuser axis. Although you usually adjust the secondary mirror tilt to aim the laser at the primary mirror center spot--you are actually aligning the focuser axis. Many users believe they are actually aligning the secondary mirror, but you can quickly prove to yourself what's really happening by either rotating the secondary mirror or adjusting it closer to or further from the primary mirror. No matter what you do to the secondary mirror placement, you can always adjust the tilt screws to align the focuser axis with a thin beam laser.

The confusion then is how do you properly place (rotation and fore and aft adjustments) the secondary mirror under the focuser so the three alignments (primary mirror and focuser axes and secondary mirror placement) are all corrected simultaneously? The answer lies in separating the axial adjustments (the axial lines that define the primary mirror and focuser axes--or the centers of the circles) from the secondary mirror alignment (the edges of the circles).

The first adjustment is always secondary mirror alignment. This involves aligning three circles--the bottom edge of the focuser drawtube, the actual edge of the secondary mirror, and the reflected edge of the primary mirror. Assuming the secondary mirror is reasonably centered in the OTA and the focuser is reasonably "squared" to the OTA, you can optimally place the secondary mirror by adjusting its rotation, fore and aft position, and relative tilt. When the three circles are concentric, the primary mirror center spot should also be almost perfectly centered, which leads to the second, focuser axial adjustment. After you've tweaked the focuser axial alignment with the thin beam laser, you need to make the third, and final, primary mirror adjustment with the collimation cap. Always make the adjustments in the sequence described. If you go back to tweak the focuser axial alignment, always finish with a precise primary mirror alignment.

I suspect the discrepancy between the various reads is related to the tools you're using. While the collimation cap does a good job aligning the primary mirror, it's not the best tool for optimally placing the secondary mirror. Even a small error (+/-0.1-inch or 1-percent of the primary mirror reflection diameter) is an obvious error when using a thin beam laser to align the focuser axis. I also suggest verifying the thin beam laser accuracy in the focuser by rotating (and resecuring the locking screw between reads) the laser and observing the position of the beam relative to the primary mirror center spot. Without a Paracorr, this alignment can be +/-0.3-inch, but I prefer to verify the laser to at least +/-0.1-inch (with a Paracorr, the tolerance is reduced to +/-0.05-inch).

Barlowing a side window laser is OK for coarse primary mirror alignment, but I suggest following this coarse alignment with your collimation cap (which should also be verified through various rotated positions in the focuser drawtube). If the collimation cap consistently agrees with the side window Barlowed laser (within +/-0.02-inch), you can probably skip the final tweak with the collimation cap. If the two tools differ significantly, even if it's 80-percent hit, 20-percent miss, you should always finish with the verified collimation cap.


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mwtse
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Reged: 06/03/11

Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4862091 - 10/15/11 09:20 AM Attachment (96 downloads)

I find that the secondary mirror is not positioned at the center of the spider, should I center the spider or offset the spider so that the mirror is centered in the optical tube?

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mwtse
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Reged: 06/03/11

Re: How to Collimate your Newtonian new [Re: mwtse]
      #4862122 - 10/15/11 09:55 AM

I've found the answer:

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4222723/page/0/view/collapsed/sb/5/o/all/fpart/all/vc/1


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sixela
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: How to Collimate your Newtonian new [Re: mwtse]
      #4862529 - 10/15/11 01:52 PM

The answer is that the attachment was meant to implement a centred holder and spider and an offset diagonal -- just to be sure you jumped to the right conclusion.

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dodgerm37
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Reged: 02/10/12

Loc: N.E Ohio, USA
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5069409 - 02/12/12 06:52 PM

Does anyone have "RECENT" instructions for the Zhumell Z-10? After assembly I'm trying to check collimation on a new Z-10. Instead of the screws mentioned in instructions, mine has three white knobs and three black knobs. Has anyone run into this situation? HELP!! The skys might clear in the next few months. Thanks

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Jason D
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Reged: 10/21/06

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Re: How to Collimate your Newtonian new [Re: dodgerm37]
      #5069497 - 02/12/12 07:52 PM

I suggest starting a new thread with your question.

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NickS
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Reged: 02/17/12

Loc: Oxford, England.
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5079681 - 02/19/12 07:44 AM

Hi I'm a very new astronomer and the mirror thing worries me quite a bit. I'm fine with the process of alignmet. But is there an issue of getting the primary mirror to focus it's magnified image at an exact spot on the secondary? If that is the case, then how is that achieved?

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Jason D
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Re: How to Collimate your Newtonian new [Re: NickS]
      #5079921 - 02/19/12 10:47 AM

Can you start a new thread with your questions? Do clarify your question. It is unclear what you meant by "getting the primary mirror to focus it's magnified image at an exact spot on the secondary."

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Joe_C
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Reged: 12/14/11

Loc: Gold River, CA, USA
Re: How to Collimate your Newtonian new [Re: Jason D]
      #5232811 - 05/21/12 04:44 PM

I have a (relatively) inexpensive Dob: Zhumell Z12. I have collimated using a combination Celestron cheshire / sight tube, following (as far as possible with the tools at hand) the "Collimation And the Newtonian Telescope V4" writeup by Donald E Pensak at www.cloudynights.com/item.php?item_id=2677.
The results have been less that spectacular for viewing, even at 300X magnification:
Mars - I see the planet, but no detail
Jupiter - I see three moons, no planet detail
Saturn - I see two rings, no planet detail

I'm pretty sure that collimation is the issue, and have some questions related to this:

1. Is this scope and its Crayford focuser of good enough quality to purchase and use the Catseye system of collimation products?

2. I would like to remove the primary and check / replace the center spot, but (being new to this hobby) I am quite nervous about removing the primary. I looked at: http://www.cloudynights.com/ubbarchive/showflat.php/Cat/0/Number/1552280/page/0/view/collapsed/sb/1/o/all/fpart/1. Since I will be doing this alone, I would rather not have the tube standing upright on the floor. I would like to leave it in its "cradle", and (somehow) support the primary as I remove the screws. Any help / thoughts on accomplishing this would be greatly appreciated.


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Husbyggarn
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Reged: 12/12/08

Loc: Sweden
Re: How to Collimate your Newtonian new [Re: Joe_C]
      #5233553 - 05/22/12 03:25 AM

I also used a Cheshire/sight tube but was never satisfied with the views i was getting, i always suspected the collimation was not correct.
Finally i bought a laser collimator and a 2x barlow. I payed about 100$ for both.
First i use the laser without barlow to center the laser dot on the primary mirror center marking by adjusting the secondary mirror and looking down the telescope. When that is ok i use the laser with the barlow, and now since the laser beam is wider i get a reflection of the whole primary mirror doughnut center marking on the lasers collimator's tilted viewing screen, now i center the reflection by adjusting the primary mirror.
I always do this before every viewing session and it takes about 5 minutes now.
Then i know that the scope is working at optimum so i don't have to worry about that.
Well worth the investment and the time.
Oh, and wait about 30 mins to let the mirror cool down before doing serious observations.


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Joe_C
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Reged: 12/14/11

Loc: Gold River, CA, USA
Re: How to Collimate your Newtonian new [Re: Husbyggarn]
      #5233698 - 05/22/12 08:15 AM

After reviewing Astro Baby's "A Simple Guide to Collimating a Newtonian Reflector" writeup: http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm
I'm beginning to think that I may have a scope with damaged optics.

The airey disk I see in Intrafocus and Extrafocus looks very much like his last image of an "Optical Surface Damaged - defocused". There are no concentric "rings", just outward-radiating ring-like "spikes". They are interesting / almost beautiful to look at, but certainly not "rings" as seen in the other images.

Any suggestions about how I might take a picture of one through my (Dobsonian) eyepiece, so that I can post it here online to show what I am seeing?


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Husbyggarn
sage


Reged: 12/12/08

Loc: Sweden
Re: How to Collimate your Newtonian new [Re: Joe_C]
      #5236020 - 05/23/12 04:24 PM

I don't think your optics is damaged, it may just be atmospheric turbulence.
You may have to look for a while to catch those moments when the atmosphere is steady.

IMHO, I would advise you to invest in a laser collimator and barlow. Then you can atleast narrow the issue down when the scope is properly collimated.


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JoeM101
scholastic sledgehammer


Reged: 04/09/12

Loc: 45.66086, -73.54702
Re: How to Collimate your Newtonian new [Re: Husbyggarn]
      #5255014 - 06/04/12 05:09 PM

I have a question for Vic, I also have an f/4 scope, mine with a Baader MPCC (multi purpose coma correcter), when collimating, do I take the MPCC out or can it be done with it in?? What difference does it make if any and what is the recommendation for faster coma corrected scopes?

One more thing, if i may...
I have to say that reading Vic's thread(s), JasonD, sixela, and Nils, have opened my eyes a little wider with regards to collimation. Though at times the esoteric eludes me, all in all, they have given us the very best and most detailed explanations imaginable and i for one am absolutely thrilled that these people put in the time to share with all of us their vast collective knowledge and experiences. i'm getting better at collimation, slowly but surely and understand more than ever, though i have to say, if anyone is interested in watching a video on collimation, this guy (Dion) isn't so bad Advanced Newtonian Collimation he has a way about him.. fun to watch! It may be a tad simplistic , but i think you will enjoy it, for what it's worth, not the best but offers a different prespective although doesn;t cover all the points.
Anyhow, armed with the knowledge gained on CN, with kudos to Vic, Jason , Nils , sixela, and last but not least Howie Glatter, compliment your skills... while looking at differing methods and perspectives. the more you learn, the the easier collimation gets, since the whole process has a bit of a learning curve involved.

keep an open mind but most of all open eyes

clear skies!!!


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Jason D
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Re: How to Collimate your Newtonian new [Re: JoeM101]
      #5255964 - 06/05/12 10:41 AM

Hello Joe,

Thank you for the kind words.

Quote:

if anyone is interested in watching a video on collimation, this guy (Dion) isn't so bad Advanced Newtonian Collimation he has a way about him




Unfortunately, references to the above video have been popping up in various forums. It is unfortunate because Dion makes a serious misleading claim. He discredits laser collimators by stating that laser collimators “lie.” Dion made the mistake of expecting laser collimators to be used to center/round the secondary mirror under the focuser. Unless a laser collimator is used with a holographic attachment, it is not expected to center/round the secondary mirror under the focuser.

Jason


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JoeM101
scholastic sledgehammer


Reged: 04/09/12

Loc: 45.66086, -73.54702
Re: How to Collimate your Newtonian new [Re: Jason D]
      #5256093 - 06/05/12 12:40 PM

Quote:

Hello Joe,

Thank you for the kind words.

Quote:

if anyone is interested in watching a video on collimation, this guy (Dion) isn't so bad Advanced Newtonian Collimation he has a way about him




Unfortunately, references to the above video have been popping up in various forums. It is unfortunate because Dion makes a serious misleading claim. He discredits laser collimators by stating that laser collimators “lie.” Dion made the mistake of expecting laser collimators to be used to center/round the secondary mirror under the focuser. Unless a laser collimator is used with a holographic attachment, it is not expected to center/round the secondary mirror under the focuser.

Jason




Jason, i agree that he goes a little far with regards to laser collimation in saying that they lie, hence my comment that it's a tad simplistic and doesn;t cover all the points. He does say that the laser is not intended to line up your secondary though, even though with a holographic attachment, as you stated, you certainly can... but anyhow, i wanted to see if you or any of the others, Vic? Nils?, Alexis (sixela).. would have a gander at a thread i started with regards to using a coma correcter while collimating and give some feedback as Howie has stated you guys (ray-tracers lol) were probably able to give some insight

The thread: Help Collimating an F/4 with coma correction

Since Vic is also using a coma corrected F/4, he may be able to shed some more light on this

thanks


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