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General Astronomy >> Beginners Forum

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Jason D
Postmaster
*****

Reged: 10/21/06

Loc: California
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: spencerj]
      #5643329 - 01/25/13 08:46 PM

Quote:

... but what if someone asks about obtaining perfect collimation with an autocollimator? Well . . . I hope they were serious, because that will elicit a serious response




Who woke me up from my slumber? I thought I heard the word "autocollimator"


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panhard
It's All Good
*****

Reged: 01/20/08

Loc: Markham Ontario Canada
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: Jason D]
      #5643458 - 01/25/13 10:10 PM

You did. How was your nap.

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beatlejuice
Pooh-Bah
*****

Reged: 04/05/11

Loc: Hamilton, ON,Canada
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: spencerj]
      #5643673 - 01/26/13 01:12 AM

Quote:

Does the beginner need to know which reflection in an autocollimator is "P" or "1" or "2" or "3"? Probably not





You are probably right, and I don't yet own an autocollimator, but I sure as heck am glad that if or when I do get one, that information is available on this wonderful forum.

Eric


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kenrenard
Carpal Tunnel


Reged: 12/13/12

Loc: Dunmore, PA
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: Jason D]
      #5643891 - 01/26/13 07:43 AM

Quote:

Quote:

... but what if someone asks about obtaining perfect collimation with an autocollimator? Well . . . I hope they were serious, because that will elicit a serious response




Who woke me up from my slumber? I thought I heard the word "autocollimator"




I had no idea what you guys were talking about. Until I googled and found your post.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3532750/page...

I used the post below to really learn what I should see.

http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Board=reflector...

I think the most important sentence was
:Here is a photo of a well-aligned secondary mirror."

And then this
IMPORTANT:
1- Do not evaluate the primary reflection clipping unless you have completed at least the focuser axial alignment step. That is, if the primary mirror center spot is not located under the cross hairs of the sight-tube, clipping visual information is false or unreliable.
2- Seeing the whole primary reflection is not enough. You need to move your head back until the primary reflection edge overlaps with the secondary mirror edge. You need to be looking through the sight tube during this evaluation
3- Do your best. Perfect secondary alignment is not necessary unless you have a relatively small secondary mirror.

Thank you Jason for your in depth posts with pictures. It was very helpful and got me to where I am today which was seeing the (nice doughnut shape) in my star test and getting very nice detail on Jupiter.

Ken


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Eric63
scholastic sledgehammer


Reged: 06/16/12

Loc: Ottawa, Ontario
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: kenrenard]
      #5644156 - 01/26/13 10:51 AM

I took my 150 Newt out last night to test my collimation. Althought cold (-10F) there was no wind and I was able to stay out for sime time. I tested it on Jupiter and the detail was amazing. Three bands were clearly visible and I could even make out some detail comming out of the NEB, I think they may heve been festoons. The seeing was not the greatest but there were times when it popped clearly into view. I could not make out colour like in my Mak, but the sharpness was just as good. I had one of the best views of Jupiter so far! I then did a star test on Sirius and the rings were very nice but I think they could still use a bit of tweaking. I was not going to take my gloves off at that temperature and so I kept observing. One thing i noticed duirng the star test was that the outside ring was cut off slightly where the mirror clips are located. I guess that this is normal for a Newtonian and nothing related to my collination. Since I never did a star test with this telecope before and can't say if this was there before the collimation.

Eric


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Jason D
Postmaster
*****

Reged: 10/21/06

Loc: California
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: kenrenard]
      #5644355 - 01/26/13 12:53 PM

Quote:

Thank you Jason for your in depth posts with pictures. It was very helpful and got me to where I am today which was seeing the (nice doughnut shape) in my star test and getting very nice detail on Jupiter.

Ken







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Dennis_S253
Pooh-Bah


Reged: 11/22/11

Loc: West Central Florida
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: Jason D]
      #5644538 - 01/26/13 02:46 PM

A question... I thought that when adjusting the secondary that you where looking for the secondary to be centered in the focuser and round. Then you adjust the tilt until you can see the main mirror clips. Is this not right?

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Vic Menard
Post Laureate
*****

Reged: 07/21/04

Loc: Bradenton, FL
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: Dennis_S253]
      #5644565 - 01/26/13 03:01 PM

Quote:

A question... I thought that when adjusting the secondary that you where looking for the secondary to be centered in the focuser and round. Then you adjust the tilt until you can see the main mirror clips. Is this not right?



The process is iterative. In that sense, it matters little which comes first.

That said, when I adjust the secondary mirror tilt, I'm reaiming the focuser axis. I'm not looking at the primary mirror clips as much as I'm looking at the sight tube cross hairs intersection (or laser dot) relative to the primary mirror center spot.

When I'm correcting the secondary mirror placement, I'm looking at the concentricity of three circles--the bottom edge of the sight tube, the real edge of the secondary mirror, and the reflected edge of the primary mirror. Since the primary mirror clips are located around the reflected edge of the primary mirror, this is where I would use that signature. I usually limit the correction adjustment to rotation and/or movement closer to or farther from the primary mirror (long axis)--not secondary mirror tilt (although it may difficult to avoid imparting some tilt when making the long axis adjustment).


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panhard
It's All Good
*****

Reged: 01/20/08

Loc: Markham Ontario Canada
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: Vic Menard]
      #5645039 - 01/26/13 08:03 PM

There we go you have heard from out 2 best. Jason and Vic I have Vic's book it is simply amazing.

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Vic Menard
Post Laureate
*****

Reged: 07/21/04

Loc: Bradenton, FL
Re: Collimation, Posts, and Star Tests. Pays Off! new [Re: panhard]
      #5645109 - 01/26/13 08:48 PM

Thanks Herb.
The truth is, if not for the fortuitous insights I gained from helping so many people in this forum, and the support I received from Jim Fly and Jason Khadder (another brilliant contributor and graphic artist that I met in this forum), there wouldn't have been a fifth edition of New Perspectives...

I am humbled by, and grateful for, this remarkable community!


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