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How to Collimate your Newtonian

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#76 Jason D

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Posted 19 April 2011 - 06:45 PM

If you are happy with that video and would like to share it with others, that is absolutely fine.
However, your words about Vic, Nils Olof, and Don were completely unnecessary – especially in a sticky thread. If you find their writing confusing, many others find the same writing helpful.
By the way, that video does not cover other aspects of good collimation such as how to optimally position the secondary mirror under the focuser.
If you want to discuss, I suggest starting a new thread. Leave this one alone.
Jason

#77 Vic Menard

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Posted 19 April 2011 - 07:34 PM

Collin,
I watched the youtube video you've described as "the absolute best collimation guide for the collimation-averse". The procedure is similar to the one I use with my scope when assessing and correcting the focuser and primary mirror axial alignments. I use a better laser with my procedure because I need better precision for my f/4 coma corrected Newtonian's axial alignments.

An economy laser may be sufficient for a longer focal ratio optic--ymmv. Of course, if you only use the procedure as demonstrated in the youtube video, it's quite likely the secondary mirror will soon need additional help. If you read through the last few posts in this thread (just page 4 should be enough), that's more or less what we've been discussing.

Finally, I don't speak any Slavik tongues either, but I do recognize that sometimes, trying to actually understand collimation principles can cause one's eyes to "glaze over" and having to deal with the often less than precision alignment mechanisms found in many economy Dobsonians can cause one's teeth to gnash and one's hands to wring. Id est quod id est.

To close, I think this quote by Albert Einstein is appropriate, "Make everything as simple as possible, but not simpler."

#78 fender2547886

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Posted 20 April 2011 - 11:54 AM

Hi Everyone,
I own the new at 12" f4 reflector and am beginning to love it. But I have a question.
1-I collimate the tube with it is a horizontal position.
2-I use the Orion deluxe collimator.
3-I have the laser pointed dead center on the mirror.
4-I have the return beam of the laser perfectly aligned on the primary mirror.
5-But when I leave the laser on and move the sope to a more vertical position the return laser beam from the primary is shifted and is not centered no longer on the center hole on the Orion Laser Collimator.
6-I did add washers to the outside of the spider since the spider nuts where too short .
7-everything is locked down.
8-Is this normal or is the primary shifting?
I would love some input.
Danny
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#79 hiddenwolf

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Posted 20 April 2011 - 04:20 PM

you want to collimate your scope with the ota level with the horizon so on its side. also rotate the laser in the focuser and watch the beam on your primary and see if it stays motionless , if it wobbles then your laser is out of collimation. also check for slop in your focuser tube clamp.

#80 nheacock

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Posted 20 April 2011 - 04:54 PM

Generally speaking, that's good advice, but I can tell you that if I collimate my 16" Meade Lightbridge when it's level I'd see nothing in collimation because as soon as I raise it 20 degrees or so it's out again. This is because of shift in the primary and slop in the overall design of the trusses.

I always collimate at 50 or 60 degrees or so altitude (which of course means exceedingly careful handling of the tools).

If I stick my laser in the focuser and move the scope in altitude, the dot moves on the primary. Not because the laser is out of collimation, but because of the play in the system. Danny is likely experiencing some form of this as well.

It's not uncommon for large Newts (Truss Dobs in particular, though Danny didn't mention what form of reflector he's got) to have collimation shift at different altitudes. In my case, the Meade Lightbridge in particular is more severe then what I've seen on others, either ATM or commercial. I'd say from personal experience of looking through dozens of Dobs ranging from 12" to 40" that I've never seen one hold perfect collimation at all altitudes (with rigid, high tension string Dobs performing the best).

So my advice to someone who has this problem is to collimate in the middle of your typical viewing altitude and you'll go out the least at either extreme.

-Neil

#81 Jason D

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Posted 21 April 2011 - 09:10 PM

http://www.cloudynig...5/o/all/fpart/1

#82 Tesselator

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Posted 14 June 2011 - 07:02 PM

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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#83 Jason D

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Posted 14 June 2011 - 09:46 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


#84 Twilight

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Posted 15 June 2011 - 12:53 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.

#85 Tiebreaker

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Posted 05 September 2011 - 03:09 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 :grin:) 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??

#86 Vic Menard

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Posted 05 September 2011 - 04:05 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.

#87 mwtse

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Posted 15 October 2011 - 08:20 AM

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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#88 mwtse

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Posted 15 October 2011 - 08:55 AM

I've found the answer:

http://www.cloudynig.../fpart/all/vc/1

#89 sixela

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Posted 15 October 2011 - 12:52 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.

#90 dodgerm37

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Posted 12 February 2012 - 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

#91 Jason D

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Posted 12 February 2012 - 07:52 PM

I suggest starting a new thread with your question.

#92 NickS

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Posted 19 February 2012 - 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?

#93 Jason D

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Posted 19 February 2012 - 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."

#94 Joe_C

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Posted 21 May 2012 - 03:44 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.cloudynig.../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.

#95 Husbyggarn

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Posted 22 May 2012 - 02:25 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.

#96 Joe_C

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Posted 22 May 2012 - 07:15 AM

After reviewing Astro Baby's "A Simple Guide to Collimating a Newtonian Reflector" writeup: http://www.astro-bab...ation guide.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?

#97 Husbyggarn

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Posted 23 May 2012 - 03:24 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.

#98 JoeM101

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Posted 04 June 2012 - 04:09 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!!!

#99 Jason D

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Posted 05 June 2012 - 09:41 AM

Hello Joe,

Thank you for the kind words.

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

#100 JoeM101

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Posted 05 June 2012 - 11:40 AM

Hello Joe,

Thank you for the kind words.

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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