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How to Collimate your Newtonian

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#26 Paulin

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Posted 27 September 2008 - 08:23 PM

Hello Vic. Thank you for your answer. Here in Mexico City I have had cloudy nights everyday, but I´m sure that this mak-new telescope is discollimated because I can see that the secondary was turned during the transport. I have not tried to evaluate the telescope because I´m searching for a complete way to collimated this kind of optics. With respect a tools collimation I have your book ( fourth edition)with the three basic tools. I have too a barlowed laser. I have collimated my reflectors but this mak is different. I can use the general guidelines to collimate this optics but I don´t have any idea about how to do the primary collimation or how to move the secondary if this is neccesary.

Thanks a lot Vic
Regards
Paul

#27 Vic Menard

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Posted 28 September 2008 - 12:01 PM

...Here in Mexico City I have had cloudy nights everyday, but I´m sure that this mak-new telescope is discollimated because I can see that the secondary was turned during the transport...

I've had some experience collimating a similar scope for a friend. His secondary mirror was also rotated out of alignment and routine axial alignment with a simple thin beam laser did not improve the image performance. Like a Schmidt/Newt, this scope is collimated by aligning the corrector axis (the axis of the meniscus lens) to the focuser axis.

Since there's no accommodation for rotating the secondary mirror, we gambled and rotated the meniscus lens (and the secondary mirror with it) in its cell (followed by routine axial alignment to correct the secondary mirror tilt) until the skewed secondary mirror looked "textbook." As I recall, the OTA was pretty long and the secondary mirror appeared to be mounted centered relative to the meniscus, so the final alignment was centered, not offset. The image performance improved dramatically after the secondary mirror alignment was corrected.

As I said--it's a gamble. In this case I don't think you have much to lose, worst-case scenario you send it back for realignment. We got a lot of fingerprints on the meniscus lens making the rotational adjustments, but they cleaned off easily after the alignment was corrected. (You can index the meniscus "starting point" for reference somewhere along the edge with a permanent marker if you decide you would like to undo the meniscus rotation adjustment.)

#28 Paulin

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Posted 29 September 2008 - 05:57 PM

Hello Vic, thank you for the information. I have some questions about this collimation that you did with a similar scope.

Does the secondary mirror can be aligned in axial way but not can be rotated?... You had to move all the meniscus, so I suppose that the secondary does not have independent movement. When you say about aligning the corrector axis to the focuser axis if I understand well, there is only a right position to left the meniscus lens. If only the meniscus lens is turned and the secondary not ( the secondary keeping his right position), this is going to affect the performance on this kind of telescope?..

Sorry for so many questions. The collimation seems to be something harder that in standars newtonians.

Regards
Paul

#29 Vic Menard

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Posted 06 October 2008 - 09:00 AM

Does the secondary mirror can be aligned in axial way but not can be rotated?...

Is this the scope you're trying to collimate?
http://www.cloudynig...hp?item_id=1548

You had to move all the meniscus, so I suppose that the secondary does not have independent movement.

The reason I asked if you're trying to collimate an Intes Micro MN66 is that I just got back from the Peach State Star Gaze where I was asked to collimate a MN86, which did accommodate secondary mirror rotation. I had to loosen a knurled retaining ring (after removing the screw-on cover to expose the tilt adjustment screws.) The knurled retaining ring had a small set screw that had to be loosened with a jeweler's screwdriver, but once the ring was loosened, secondary mirror rotation and tilt were readily adjustable.

When you say about aligning the corrector axis to the focuser axis if I understand well, there is only a right position to left the meniscus lens. If only the meniscus lens is turned and the secondary not ( the secondary keeping his right position), this is going to affect the performance on this kind of telescope?..

Perhaps--but if your scope is an Intes Micro, and it has the same secondary mirror alignment adjustment as the MN86, you won't have to rotate the meniscus.

Sorry for so many questions. The collimation seems to be something harder that in standars newtonians.

Although making fine adjustments to accurately align the secondary mirror can be tedious, from what I've read about the optical configuration, the scope is supposedly more tolerant of small axial misalignments when compared to a simple f/6 Newtonian.

FWIW--when I was reading about the scope (in a recent edition of Astronomy Technology Today), I was led to believe that the knurled retaining ring setscrew enabled the user to simply twist the knurled retaining ring to adjust the secondary mirror rotation. On the scope I collimated, the ring needed to be loosened first, as it was tight enough to prevent manual rotation (at the meniscus). I suspect the rotation alignment error resulted after someone accidentally loosened two or more tilt adjustment screws at the same time, allowing the secondary mirror to rotate on the central mounting screw...
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#30 Timber

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Posted 08 November 2008 - 08:11 PM

Vic, I posted in the wrong place, I'll try this. Do you have a link to Tectron, I have been unable to find their website for the Infinity XL Autocollimator and Cheshire. Thanks

#31 CatseyeMan

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Posted 08 November 2008 - 11:54 PM

Vic, I posted in the wrong place, I'll try this. Do you have a link to Tectron, I have been unable to find their website for the Infinity XL Autocollimator and Cheshire. Thanks


I sent you a PM.

Regards,

#32 Timber

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Posted 09 November 2008 - 03:09 PM

Thanks Jim, I don't know what a PM is but I found your website, will be in touch

#33 Don W

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Posted 09 November 2008 - 03:45 PM

PM is a private message. Look at the top left of your Cloudy Nights screen for a blinking envelope.

#34 Gianluca67

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Posted 05 December 2008 - 12:39 PM

Thank you all for this interesting thread. I have an f/4 Newtonian so collimation is crucial to get good images. I use a sight tube and fine align on a star whenever the seeing is excellent. The curious thing is that although the in focus star seems to be perfectly circular with concentric rings the shadow of the secondary mirror of the defocused star is shifted. The amount of the shifting is higher if I defocus inward (10-12 wavelenghts). Does it mean that collimation is wrong? I can often use extremely high power if the scope is at thermal equilibrium.
Thanks
Gianluca

#35 jayw65

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Posted 03 April 2009 - 09:10 AM

Is this confusing or what? I hope when I get my Astro Sky 15" it will not be so perplexing. It has not been a big problem with the 8" Orion I am currently using or maybe ignorance is bliss.

Jay W

#36 Vic Menard

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Posted 14 August 2009 - 01:23 PM

Here are some great animations provided by Jason D if you're sorting out a secondary mirror alignment error: link

#37 RedIrocZ-28

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Posted 02 November 2009 - 02:21 PM

Vic, I read this thread the other day and waited for a good clear night for a star test. I've been a fan of "Well, its close enough" for the last few years. I found it very hard to collimate my 10" newt because of the low eyepiece, and having to sit in a chair to view, get up, turn a knob on the mirror cell, then back to the eyepiece and find the star has completely left the field of view. Until last night where I put my scope up on the deck right at the edge of the stairs, where I could stand up and look through the EP, then reach down to twist the knobs vs. having to get up out of the chair, etc. etc.

What I found was that my Primary Mirror center spot is not exactly on center. Very very close, but not centered. The star test revealed a misaligned optical train. I made a drawing to represent what I saw in the Eyepiece,i.e. how the Startest (at 300x) vs. the Centerspot looked visually.

Posted Image

Collimation is easy once it "clicks" in your head. Get it close with your collimation tools, then spend 15 minutes tweaking the collimation screws to get the diffraction rings of a nice Bright defocused star to look concentric.

The short views of the moon I got before the clouds rolled in with the diffraction rings very much concentric was the best views I have ever had!

Thanks, Vic!
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#38 Vic Menard

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Posted 02 November 2009 - 03:30 PM

Brad, have you considered replacing the triangle and getting the new one accurately centered? Or perhaps "dotting" the existing triangle (on the right side in your graphic) to remind yourself where the optimal Cheshire alignment is with your slightly off-center triangle? It could save you those 15 minutes of tweaking the primary mirror alignment on a star.

Of course, if you prefer fine aligning the primary mirror on a star each time you observe, that's OK too!

#39 RedIrocZ-28

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Posted 02 November 2009 - 04:27 PM

Vic, I actually did that centerspot myself! LOL! It can only be off by a little bit, but I think that I'll be doing a star test from now on. Bad seeing was another factor in me not collimating the scope using a star test in the past. Its difficult when the defocused star looks like a flickering candle flame. Last night was very nice until the clouds rolled in. And it was much easier doing a star test with a star closer to the North star with my non-tracking Dob, they don't move as much. ;)

Hopefully my imaging will improve significantly as well. I had a great night with Jupiter about a month ago where I was told by Lunatiki that my collimation was off, badly, because the shadow on the face of Jupiter was elongated.

here is the image, the top dark spot is the moon shadow, the bottom dark spot is Callisto(I believe). You can see the elongation due to bad collimation. The moon shadow should be perfectly circular for those who are wondering what it should look like. Posted Image
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#40 Vic Menard

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Posted 02 November 2009 - 04:43 PM

Interesting.
Here's an image of Saturn taken moments after aligning the primary mirror with a Barlowed Glatter laser: Saturn

How many images did you stack for your Jupiter image?

#41 RedIrocZ-28

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Posted 02 November 2009 - 05:00 PM

I do not remember exactly how many frames this was but its over 400 for sure. I usually get a grainy look with anything under 400. ToUcam840k, 5fps, @ F/22. :)

#42 Vic Menard

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Posted 02 November 2009 - 05:17 PM

Is there any possibility that the elongated moon and shadow are the result of motion? In 80 seconds the planet rotates about 1/2 of 1-percent of the diameter, moon speed could be more. It's certainly possible that the elongation is a collimation artifact, but looking at the rest of the surface detail, I don't know... Are you convinced?

#43 auriga

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Posted 02 November 2009 - 07:54 PM

Thanks Vic, this is a very clear and useful summary (except for the autocollimator section of course). I have marked this as a "favorite thread" so I can refer to it in the future.
(But if it reaches 300 posts with 100 diagrams I am out of here. :-) )
Regards,
Bill Meyers

#44 Jason D

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Posted 02 November 2009 - 09:01 PM

But if it reaches 300 posts with 100 diagrams I am out of here. :-)

:thinking: :scratchhead: :hmmmm: :shameonyou: :lol:

#45 RedIrocZ-28

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Posted 11 November 2009 - 02:59 PM

Vic, I am pretty convinced that it is (was) a collimation problem. The raw frames show the elongated moon shadow.

Have not had a night with a shadow transit to verify now that I have circle shadows though. Hope to have the scope out tonight.

Vic, another thing that is bugging me, I know that the secondary is centered in the tube via measuring the distance from the center screw of the secondary mount to the tubes edge. Anyway, when you shine a lightsource down the tube, or are pointed at the moon, and you look down the tube and see the shadow of the secondary, the circular shadow is noticibly off center, like by 3/4" if not more. I have tried with a high intensity flashlight to see if the shadow changes location when the flashlight is held at different locations around the circumference of the tube, but the shadow doesn't move. Its always biased toward the focuser.

Is this normal?

#46 sixela

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Posted 11 November 2009 - 03:53 PM

Yes. There are enough threads about diagonal offset elsewhere not to pollute this master thread with a more thorough explanation ;).
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#47 RedIrocZ-28

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Posted 11 November 2009 - 04:08 PM

sixela, you're right. :) Mods, remove my post if you feel necessary.

#48 Merijn

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Posted 25 February 2010 - 01:14 PM

Could I ask a question in this present thread about collimation or do I need to open a separate one?

If yes:
I did some work on the focuser so needed to collimate again.
I checked if the secondary was exactly under the focuser using white and blue papers to distinguish between the different edges.
After that was fine I roughly collimated with a laser.
Then used the infinity xlk.

Here's the problem:
I can stack P with P2 but then the reflection P1 is slightly off center. I can't get all three triangles stacked.

What error is this and how can I resolve this?

Thanks.

#49 Jason D

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Posted 25 February 2010 - 01:26 PM

Start a new thread... Many of us will help.

#50 kev721

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Posted 21 April 2010 - 04:13 PM

If the star test works, is it safe to assume everything is aligned correctly, or could the alignment still be suboptimal?

Is there a poor-man's artificial star that anyone would recommend? (Maybe a simple DIY?)


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