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Equipment Discussions >> Reflectors

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Jason D
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Reged: 10/21/06

Loc: California
Re: Concise thread about autocollimators+improvements new [Re: hudson_yak]
      #3535621 - 01/02/10 06:28 PM

I see your point, Mike
I edited the post. I removed all ratings and replaced them by "check" marks. OK, I left two checks for what I consider to be highly accurate alignment but I did not explain it.
I did not want to delete the post because understanding which errors each tool checks for is important.
Jason

Edited by Jason D (01/02/10 09:03 PM)


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demiles
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Reged: 11/07/06

Re: Concise thread about autocollimators+improveme new [Re: Jason D]
      #3536982 - 01/03/10 12:17 PM

Jason, I have read over your info and find it quite interesting. I have never used a AC to collimate but do use a site tube to align the secondary and a barlowed laser to align the primary. I double check with a cheshire and all seems well. My question is how easy is the AC to use in the dark? The reason I ask is because once my entire scope reaches ambient temp the collimation does shift a small amount. My Obsession will do it and yes it is repeatable in the same direction all the time. My Discovery also did this as well. I collimate just after setting up then have to recheck the primary after 3-4 hours. There is usually a temp. drop of 20 degrees + during this time.

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Jason D
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Re: Concise thread about autocollimators+improveme new [Re: demiles]
      #3537114 - 01/03/10 01:15 PM Attachment (167 downloads)

Quote:

My question is how easy is the AC to use in the dark?



I use a clip-on light source as shown in the attachment. To preserve eye adaptation, I added few red translucent layers to the light source. You could also clip the light source to the vanes.
Jason


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turtle86
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Reged: 10/09/06

Re: Concise thread about autocollimators+improveme new [Re: Jason D]
      #3537227 - 01/03/10 02:17 PM

Excellent idea. Do you use something like red brake light tape over the light?

Quote:

Quote:

My question is how easy is the AC to use in the dark?



I use a clip-on light source as shown in the attachment. To preserve eye adaptation, I added few red translucent layers to the light source. You could also clip the light source to the vanes.
Jason




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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Concise thread about autocollimators+improveme new [Re: demiles]
      #3537257 - 01/03/10 02:29 PM

Quote:

Jason, I have read over your info and find it quite interesting. I have never used a AC to collimate but do use a site tube to align the secondary and a barlowed laser to align the primary. I double check with a cheshire and all seems well. My question is how easy is the AC to use in the dark? The reason I ask is because once my entire scope reaches ambient temp the collimation does shift a small amount. My Obsession will do it and yes it is repeatable in the same direction all the time. My Discovery also did this as well. I collimate just after setting up then have to recheck the primary after 3-4 hours. There is usually a temp. drop of 20 degrees + during this time.



I have found that if I collimate perfectly when the telescope is at ambient temperature in the afternoon, I can watch the collimation changing all over the place as the telescope cools. But once it has cooled, the collimation returns. How fast this happens depends on the scope's materials, pole thicknesses, etc.


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mark Jimenez
sage
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Reged: 01/08/07

Loc: Atlanta GA.
Re: Concise thread about autocollimators+improveme new [Re: Starman1]
      #3537401 - 01/03/10 03:27 PM Attachment (184 downloads)

Hello,
I just wanted to show how Jim at Catseye helped me get the AC mirror located at the focal plane on my imaging newt. On mine, and many others that are designed for use with a coma corrector, the focal plane often resides above the top of the focuser.
This is a two pupil (XLK) autocollimator with 1.5" extension built into the barrel. Works great.
Also, I find these tools very easy to use in the dark with a small red LED flashlight.
-Mark


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Jason D
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Reged: 10/21/06

Loc: California
Re: Concise thread about autocollimators+improveme new [Re: mark Jimenez]
      #3537585 - 01/03/10 05:03 PM

Nice!!!!!!!!!
Thanks for posting the photo.
Imager enthusiasts will definitely be interested in this option.
Jason


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Jason D
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Reged: 10/21/06

Loc: California
Re: Concise thread about autocollimators+improveme new [Re: turtle86]
      #3537603 - 01/03/10 05:14 PM

Rob, I taped pieces of red translucent wrap. Here is an old photo to show you how it would look like at night. The CAM in the photo is an old makeshift CAM.



With the XLK+CAM I use two source lights: One to illuminate the center spot and another to illuminate the CAM. The production CAM will not require the CAM source light – this is what Jim is trying to resolve.

Photos below are without the red translucent wrap.


Jason


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turtle86
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Reged: 10/09/06

Re: Concise thread about autocollimators+improveme new [Re: Jason D]
      #3537809 - 01/03/10 07:15 PM

Thanks! Looks like just the ticket for using an autocollimator in the dark.

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CatseyeMan
Vendor (Cats Eye Collimation)
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Reged: 12/16/04

Loc: Madison, AL USA
Re: Concise thread about autocollimators+improveme new [Re: Jason D]
      #3537936 - 01/03/10 08:46 PM Attachment (157 downloads)

Here's what I use and recommend:

Coast Cutlery #TT75331CP LED clip light retrofitted with a bright 3000 MCD Red LED (Gilway E184 found here) and clipped to the spider; I get the best illumination with the light pulled in close to the Secondary as shown in the pics.


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Don W
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Reged: 05/19/03

Loc: Wisconsin, USA
Re: Concise thread about autocollimators+improveme new [Re: CatseyeMan]
      #3537954 - 01/03/10 08:57 PM

Slick. Me likey.

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turtle86
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Reged: 10/09/06

Re: Concise thread about autocollimators+improveme new [Re: CatseyeMan]
      #3538021 - 01/03/10 09:41 PM

Thanks, Jim. Looks great!

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Jason D
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Reged: 10/21/06

Loc: California
Re: Concise thread about autocollimators+improveme new [Re: CatseyeMan]
      #3538022 - 01/03/10 09:42 PM

Quote:

Here's what I use and recommend:

Coast Cutlery #TT75331CP LED clip light retrofitted with a bright 3000 MCD Red LED (Gilway E184 found here) and clipped to the spider; I get the best illumination with the light pulled in close to the Secondary as shown in the pics.




Ummm, I wonder if these points of light on the side have enough brightness to illuminate the CAM?


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Spaced
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Reged: 03/01/05

Loc: Tacoma, Washington, USA
Re: Concise thread about autocollimators+improveme new [Re: Jason D]
      #3538771 - 01/04/10 11:28 AM

Jason, my compliments on another superbly written and illustrated how-to manual. This is just excellent! Thanks so much for sharing your knowledge!

I'm currently using only a Glatter laser + Blug to collimate my f/4.5. My secondary is properly positioned with a Catseye sight tube. Assuming I'm using these tools properly and with care, am I able to achieve sufficiently accurate collimation, such that improvement with an AC wouldn't provide noticeably better views? To make your answer of more general interest, what do you think is the fastest focal ratio for which just a good barlowed laser + sight tube provides sufficient collimating accuracy for visual use?

Thanks much.


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Jason D
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Re: Concise thread about autocollimators+improveme new [Re: Spaced]
      #3538843 - 01/04/10 12:11 PM

First, thank you for the kind words, Mike.

You asked good questions. Here is my take:

I believe the combination of:
- Quality dual-pupil autocollimator and calibrated cheshire
OR
- Dual-pupil autocollimator+CAM
will give the most accurate collimation available today. We are talking sub 0.2mm accuracy for both the focuser and primary axial alignment.

The above is factual and measureable.

What is not as factual and measurable is how accurate collimation should be? Will the use of a sub 0.2mm collimation accuracy for FAE/PAE produce noticeable difference at the EP compared to sub 0.5mm collimation accuracy? Answering this question is somewhat subjective – after all, we are not talking about the difference between 1mm and 0.2mm accuracy but between 0.5mm and 0.2mm. The scope specs, average seeing conditions, observing experience, and whether the setup is meant for imaging or visual can sway the answer from one end of the spectrum to the other. Therefore, I can’t say that the additional accuracy provided by the dual-pupil autocollimator + (cheshire or CAM) will make a noticeable difference for everyone. But what I can tell you is that you have quality collimation tools that are capable of delivering superb collimation.

Jason


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Concise thread about autocollimators+improveme [Re: Jason D]
      #3538897 - 01/04/10 12:38 PM

One way to look at it is that collimation is an envelope of accuracy.
If you are inside of the envelope, your collimation is probably good enough. You don't have to be dead center in that envelope to see good images.
However, telescopes are not static devices--they flex, sag, change shape with temperature changes.
You want to make certain your telescope stays within the envelope of good collimation--the greater accuracy you achieve, the more likely will your telescope stay within that envelope as it sags, twists, and contracts.

Plus, achieving a superior accuracy in collimation when you first set up may eliminate any necessity to check collimation during the night.

Last is the benefit of being able to see tiny changes in collimation as the scope moves up and down. Tracking down sources of sag and flexure and fixing them means the scope is better able to hold its collimation after you've spent the time to make it good.

So do you NEED to collimate to such a high precision? It depends on the scope, its targets, and its conditions of use. But, there are never any deleterious effects from collimating better than is required. After all, developing the skills of collimating using accurate tools will pay off when you get that 20" f/3 scope that uses a Paracorr.


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Vic Menard
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Reged: 07/21/04

Loc: Bradenton, FL
Re: Concise thread about autocollimators+improveme [Re: Jason D]
      #3539029 - 01/04/10 02:03 PM

Quote:


I believe the combination of:
- Quality dual-pupil autocollimator and calibrated cheshire
OR
- Dual-pupil autocollimator+CAM
will give the most accurate collimation available today. We are talking sub 0.2mm accuracy for both the focuser and primary axial alignment.



Sub 0.2mm? I can read a calibrated Barlowed laser (PAE) to about 0.01-inch (about 0.005-inch PAE) pretty consistently--that's a direct read of PAE with no parallax error. Taking registration into consideration I would add +/-0.005 to 0.01-inch (about 0.01- to 0.015-inch PAE). Assuming you're interpreting PAE from CAE and LAE, what do you consider the read accuracy of the individual alignments--or are you assuming both can be consistently read to better than 0.1mm accuracy (without detailed examination of a closeup image)? I know that both errors (CAE and LAE) contain PAE and FAE components, but balancing one against the other doesn't necessarily improve the resolution of the interpreted errors. What do you feel are the best, and worst case scenarios?

If Mike is using a Glatter laser and Blug to align the axes of his 14.5-inch f/4.5 optic, he should have no problem keeping the FAE in tolerance (+/-0.4-inch), even if he's using a Paracorr (+/-0.07-inch). The PAE high magnification tolerance (+/-0.018-inch) should also be manageable with a Barlowed laser solution (although I would recommend the 1mm Glatter aperture stop over the Blug for the best precision).

I apologize for coming into the discussion this late (three pages already). It was a busy holiday with lots of family get-togethers.

Twenty-plus years ago, when I first persuaded Tom Clark to include the "complicated" autocollimator in the 3-tool Tectron arsenal, I never imagined it would be studied in such detail and modified to utilize the new CAE and LAE alignments! If you continue on this path, the autocollimator will eventually have to either auto collimate or make coffee--but I'm not sure which the end user would demand first!

Great post!


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Spaced
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Re: Concise thread about autocollimators+improveme [Re: Vic Menard]
      #3539073 - 01/04/10 02:31 PM

Quote:

The scope specs, average seeing conditions, observing experience, and whether the setup is meant for imaging or visual can sway the answer from one end of the spectrum to the other. Therefore, I can’t say that the additional accuracy provided by the dual-pupil autocollimator + (cheshire or CAM) will make a noticeable difference for everyone. But what I can tell you is that you have quality collimation tools that are capable of delivering superb collimation.




I understand that too many variables prevent a concise answer. I infer that your answer to my first, specific question is, "You're probably doing just fine without the AC."

Quote:

One way to look at it is that collimation is an envelope of accuracy.
If you are inside of the envelope, your collimation is probably good enough. You don't have to be dead center in that envelope to see good images.




That description resonates.

Quote:

So do you NEED to collimate to such a high precision? It depends on the scope, its targets, and its conditions of use. But, there are never any deleterious effects from collimating better than is required.




You just won't make a decision easy, will you?

Quote:

After all, developing the skills of collimating using accurate tools will pay off when you get that 20" f/3 scope that uses a Paracorr.




Oh yeah, I'd better start practicing right away!

Quote:

If Mike is using a Glatter laser and Blug to align the axes of his 14.5-inch f/4.5 optic, he should have no problem keeping the FAE in tolerance (+/-0.4-inch), even if he's using a Paracorr (+/-0.07-inch). The PAE high magnification tolerance (+/-0.018-inch) should also be manageable with a Barlowed laser solution (although I would recommend the 1mm Glatter aperture stop over the Blug for the best precision).




That's reassuring.


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nsldvd
sage


Reged: 10/02/08

Re: Concise thread about autocollimators+improveme [Re: Vic Menard]
      #3539147 - 01/04/10 03:19 PM

Vic, Jason (and all)
As I go through the steps (using the Glatter laser [w/1mm aperture stop] and Blug) collimation cannot be complete without the AC. But using the offset pupil seems to have eliminated two previously used procedures, the first being the center AC pupil. Apart from showing the disappearing act, cannot all AC collimating procedures be accomplish without the center AC pupil and just using the offset AC pupil? Secondly, doesn't the AC offset pupil eliminate CDP?

dave


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Vic Menard
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Reged: 07/21/04

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Re: Concise thread about autocollimators+improveme [Re: nsldvd]
      #3539269 - 01/04/10 04:19 PM

Quote:

Vic, Jason (and all)
As I go through the steps (using the Glatter laser [w/1mm aperture stop] and Blug) collimation cannot be complete without the AC.



Why not? What is the aperture and focal ratio of your Newtonian? And are you using a coma corrector? I also suggest that you verify the Blug alignment against the self-Barlow attachment to be sure that the axial alignment with normal focuser registration is the same as the self centering alignment achieved at the bottom of the focuser drawtube.

Quote:

But using the offset pupil seems to have eliminated two previously used procedures, the first being the center AC pupil. Apart from showing the disappearing act, cannot all AC collimating procedures be accomplish without the center AC pupil and just using the offset AC pupil? Secondly, doesn't the AC offset pupil eliminate CDP?



Stacking P-3 via CDP is only useful from the center pupil, allowing a direct read of FAE (magnified 2X), which may be critical in some applications. As Jason has already noted, you can iterate between CAE and LAE and achieve precise axial alignment only limited by the read precision of the signature alignments (CAM alignment and P-2 alignment from the offset pupil). But the iterative procedure may require several repetitions if the necessary precision adjustment isn't easily effected.

I think, perhaps, the more significant question is, if one finds a discrepancy between the calibrated Barlowed laser and the autocollimator using the offset pupil to assess CAE and LAE, should one trust the calibrated Barlowed laser or the autocollimator when correcting PAE? (Or should one anticipate that the residual error is exclusively FAE, since FAE is a component of both CAE and LAE?)


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