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Equipment Discussions >> Reflectors

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RedIrocZ-28
Carpal Tunnel


Reged: 09/18/05

Loc: Grand Rapids, Michigan
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3425883 - 11/02/09 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.

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Vic Menard
Post Laureate
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Reged: 07/21/04

Loc: Bradenton, FL
Re: How to Collimate your Newtonian new [Re: RedIrocZ-28]
      #3425903 - 11/02/09 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?

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auriga
Pooh-Bah


Reged: 03/02/06

Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3426160 - 11/02/09 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


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Jason D
Postmaster
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Reged: 10/21/06

Loc: California
Re: How to Collimate your Newtonian new [Re: auriga]
      #3426256 - 11/02/09 09:01 PM

Quote:

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





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RedIrocZ-28
Carpal Tunnel


Reged: 09/18/05

Loc: Grand Rapids, Michigan
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3442281 - 11/11/09 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?


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sixela
Postmaster
*****

Reged: 12/23/04

Loc: Boechout, Belgium
Re: How to Collimate your Newtonian new [Re: RedIrocZ-28]
      #3442380 - 11/11/09 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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RedIrocZ-28
Carpal Tunnel


Reged: 09/18/05

Loc: Grand Rapids, Michigan
Re: How to Collimate your Newtonian new [Re: sixela]
      #3442403 - 11/11/09 04:08 PM

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

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Merijn
member


Reged: 12/14/09

Re: How to Collimate your Newtonian new [Re: RedIrocZ-28]
      #3646892 - 02/25/10 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.


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Jason D
Postmaster
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Reged: 10/21/06

Loc: California
Re: How to Collimate your Newtonian new [Re: Merijn]
      #3646908 - 02/25/10 01:26 PM

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

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kev721
sage
*****

Reged: 01/24/10

Loc: Little Rock, AR
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3759392 - 04/21/10 05:13 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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sixela
Postmaster
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: How to Collimate your Newtonian new [Re: kev721]
      #3760501 - 04/22/10 02:32 AM

Quote:

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



It is safe to assume that the optical axis crosses the focuser axis at the focal plane, but you don't know:

-whether the focuser axis is parallel (if it isn't, the focal plane will be tilted)
-whether the secondary is placed to deliver a centred fully illuminated field.


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kev721
sage
*****

Reged: 01/24/10

Loc: Little Rock, AR
Re: How to Collimate your Newtonian new [Re: sixela]
      #3762623 - 04/22/10 11:16 PM

How do you test for those?

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sixela
Postmaster
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: How to Collimate your Newtonian new [Re: kev721]
      #3764086 - 04/23/10 04:31 PM

Quote:

How do you test for those?




Usually with good collimation tools. The effects on visual observation are extremely subtle, though the effects on wide field photos is usually not (especially for a tilted focal plane).


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kev721
sage
*****

Reged: 01/24/10

Loc: Little Rock, AR
Re: How to Collimate your Newtonian new [Re: sixela]
      #3765528 - 04/24/10 01:32 PM

So if I can see the entire primary in the secondary, then collimate with a laser, then a star test, I should be in good shape? Anything else I might miss?

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sixela
Postmaster
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: How to Collimate your Newtonian new [Re: kev721]
      #3768151 - 04/25/10 07:05 PM

Yup. Assuming of course that you adjust primary tilt while star testing.

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kev721
sage
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Reged: 01/24/10

Loc: Little Rock, AR
Re: How to Collimate your Newtonian new [Re: sixela]
      #3772090 - 04/27/10 04:37 PM

It seems the star tests usually look all right after I have done the laser. For the star test, please correct me if I am wrong here.

1. Polaris is usually an okay star to use, but at least try something near the pole to keep it in the field longer.
2. Use as much magnification as I can. Should I barlow or not?
3. If the circles are not concentric, pick a knob, turn it, and see which way it affects the star, then repeat with another knob.

Is that about it?


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sixela
Postmaster
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: How to Collimate your Newtonian new [Re: kev721]
      #3774820 - 04/29/10 03:27 AM

Quote:


1. Polaris is usually an okay star to use,




I don't like to use Polaris: it's an 18.4" separation double.

Quote:


3. If the circles are not concentric, pick a knob, turn it, and see which way it affects the star, then repeat with another knob.





You forgot one thing to mention: always centre the star perfectly before evaluating the rings.

And you can do better than throwing darts when you have to pick a knob to turn: move the knob closest to the axis from the compressed side of the rings to the expanded side, and in such a way as to move the star away from the compressed side. Then recentre the staar and evaluate again.


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kev721
sage
*****

Reged: 01/24/10

Loc: Little Rock, AR
Re: How to Collimate your Newtonian new [Re: sixela]
      #3775417 - 04/29/10 12:26 PM

What star do you prefer? Since you did not mention any problems with #2, then I assume go for maximum magnification with barlow. So, that means I should still try to get something near the pole or I'll be chasing it across the sky all night, 20' at a time.

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uniondrone
Carpal Tunnel
*****

Reged: 12/05/09

Loc: Streetlight Archipelago
Re: How to Collimate your Newtonian [Re: kev721]
      #3972971 - 08/09/10 03:09 PM


Hello,

I was wondering how critical (and how frequent) is the collimation of the secondary? If I can see all four mirror clips of the primary through the peep hole of the collimation cap, is that good enough? Or should I strive for the reflection of the primary to be absolutely centered?


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Vic Menard
Post Laureate
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Reged: 07/21/04

Loc: Bradenton, FL
Re: How to Collimate your Newtonian [Re: uniondrone]
      #3974579 - 08/10/10 11:35 AM

Quote:

...how critical (and how frequent) is the collimation of the secondary?



As long as it's not impacting imaging or visual performance, the secondary mirror alignment is the least critical of the three alignments (primary mirror axis, focuser axis, and secondary mirror).

Quote:

...If I can see all four mirror clips of the primary through the peep hole of the collimation cap, is that good enough? Or should I strive for the reflection of the primary to be absolutely centered?



For an xt10, it's almost certainly good enough for secondary mirror alignment. I'm assuming you're not also using this coarse alignment for the focuser axis.


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