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NeilMac
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Reged: 09/25/10

Loc: MedHat, AB, Canada
Collimator concerns
      #5617723 - 01/11/13 06:23 PM Attachment (15 downloads)

I checked my scope to see how it was and it looks out by an inch so I watched the Orion video and tweaked.
Well it was a bit scary in that when I adjusted the allen screws they would only loosen one way and not go in so I did what I could and got it to the edge of the ring.
I tried to loosen the center Phillips screw since i recall them doing it in an older video and scared the *BLEEP* out of me. The dot went out of site and the secondary mirror turned. So I moved it back to what looked like ok, tightened it up and left it with the point on the edge.
Went to the Primary mirror back and adjusted it their till the spot was center with the target, almost. Very sensitive adjustments and hard to adjust the spring screws with my fingers (Although it is -16c in the garage).

Tried out my 38mm on the trees but could not get it in focus so will have to wait till the stars are out.


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NeilMac
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Re: Collimator concerns new [Re: NeilMac]
      #5617728 - 01/11/13 06:24 PM Attachment (18 downloads)

Target

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Jon Isaacs
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Re: Collimator concerns new [Re: NeilMac]
      #5617747 - 01/11/13 06:33 PM

HelloThe first concern with a collimator is to make sure that the collimator is properly collimated.. If you have to really move things a long ways, it suggests that the collimator needs to be aligned.

The test for this is to rotate the collimator in the focuser while looking at the dot on the primary mirror. If should remain fixed. If it makes a circle, the the collimator is out of alignment.

Jon


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NeilMac
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Reged: 09/25/10

Loc: MedHat, AB, Canada
Re: Collimator concerns new [Re: Jon Isaacs]
      #5617769 - 01/11/13 06:46 PM Attachment (14 downloads)

Collimator ?? hmm, will have to try that when I get out their again. If it does then it suggest defective ? I dont see anything to adjust it and that probably defeats the purpose for it?

This is as close as I got to the center in case i made it worse.


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Starman1
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Reged: 06/24/03

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Re: Collimator concerns new [Re: NeilMac]
      #5617770 - 01/11/13 06:46 PM

If this picture is AFTER collimation, you're still way out.
And it's a sign your laser is way out of collimation itself.
Here are my typical laser collimator instructions:
SIMPLE INSTRUCTIONS ON COLLIMATING WITH A LASER

1. Primary mirror must have some form of centermark. A “donut” ring is the most common, but other shapes will work. It is recommended that the centermark have an opening in the center, i.e. not be solid.
2. Stand back and eyeball the outline of the secondary mirror as seen through the focuser. The secondary mirror should be adjusted up and down the tube and rotationally so that it appears round and concentric with the inside of the focuser. High precision is not necessary—close is good enough.
3. Insert the laser and tighten the setscrew. Turn the laser on. The beam should hit the center of the primary mirror. Adjust the secondary collimation screws to achieve this.
4. Modify a Barlow lens so there is a paper cover over the bottom of the Barlow. A cardboard plug will work fine. Make sure there is a hole of 1/8” to 3/16” punched in the center of the cardboard so the laser light can get out. Insert the laser in the Barlow and secure it with the screw. Insert the laser + Barlow in the focuser, secure it, and turn it on. Note: Howie Glatter offers a laser with a white surface barlow attachable to the bottom of the laser which serves the same function and is a lot more convenient.
5. The return beam of the barlowed laser will be a diffuse red glow containing the shadow of the primary mirror’s centermark. What you need to do is adjust the Primary mirror to center that shadow on the bottom of the Barlow (now you understand why the cardboard is there), making the shadow surround the small central hole in the cardboard plug in the bottom of the Barlow. This is called the Barlowed Laser Collimation protocol, and it is the MOST ACCURATE way to use a laser to collimate a primary mirror. The return beam of a simple beam laser is simply not accurate enough to achieve collimation of a Newtonian scope. The bottom of the Barlow may be difficult to see if it is very deep in the focuser, so use a small hand mirror opposite the focuser so you can see the red glow and the mark shadow on the bottom of the Barlow.
6. Howie Glatter makes a Barlow with a white face that inserts in the bottom of the focuser (on the inside of the scope). It’s called a BLUG. This Barlow’s bottom can be seen without a hand mirror. But the white cardboard on the bottom of a barlow works just as well.


FAQ:
Why can’t the return beam of a single beam laser be used to collimate the primary?
Because in order for the return beam to be accurate enough to collimate the primary, you have to have the out beam hit the center of the primary to better than 0.01”, which is a difficult level of precision to achieve when looking down the tube from the front to see where the laser beam hits the primary mirror. Plus, most laser beams are larger than that where they hit the primary mirror.

Howie Glatter lasers are expensive. Can’t I use a cheaper laser?
Yes, you can. But the cheap lasers in the market have 2 problems: 1) they come out of the box miscollimated themselves, meaning they cannot be used to align the optics because their beams are tilted relative to the line of the barrel, and 2) Their beams do not end in a point but often in a small rectangle or oval which has enough size to it that estimating the point where it hits can be a problem. FarPoint and Glatter lasers have small beam apertures that result in tiny pinpoints where they hit the mirror, and they are both internally collimated to better than 15 arc-seconds, making them more than adequately precise to align optics. You can use less expensive lasers to collimate with, but only after you have spent quite a bit of time to collimate the laser first. Even after collimation, their beam patterns are somewhat imprecise, being large dashes instead of small points. Inexpensive lasers offer no advantage for collimation over a low-cost collimation tool like the common sight tube + cheshire collimation Eyepiece (which might work better).

Do I have to Barlow the laser to check the primary in the middle of the night?
No. Once you have achieved good collimation with the barlowed laser technique, you can check the primary’s alignment in the middle of the night with the simple return of the simple beam to its source.
Just remember this will not reveal tiny errors, just large ones.


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Starman1
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Reged: 06/24/03

Loc: Los Angeles
Re: Collimator concerns new [Re: Starman1]
      #5617774 - 01/11/13 06:48 PM

Here is a link that better explains barlowed laser collimation:
http://www.cameraconcepts.com/barlowed%20laser%20collimation.pdf


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coopman
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Re: Collimator concerns new [Re: Starman1]
      #5617781 - 01/11/13 06:52 PM

http://www.youtube.com/watch?v=bE09_X43UUQ

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NeilMac
Carpal Tunnel


Reged: 09/25/10

Loc: MedHat, AB, Canada
Re: Collimator concerns new [Re: Starman1]
      #5617798 - 01/11/13 07:00 PM

Thanks!

My concern right now is the screws to adjust the Secondary mirror, their either tight or loose.

Will try again tomorrow when it warms up to -12c
Dont know if I want to bring it in to fog up.


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NeilMac
Carpal Tunnel


Reged: 09/25/10

Loc: MedHat, AB, Canada
Re: Collimator concerns new [Re: NeilMac]
      #5617833 - 01/11/13 07:25 PM

I went outside again to check the Collimator and it does look uniform.
I tried again to center it while the tube was horizontal then as i move the tube up the point also moved ??

I betcha its going to be a clear night tonight

Thanks for the vid coopman

Edited by NeilMac (01/11/13 07:26 PM)


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panhard
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Re: Collimator concerns new [Re: NeilMac]
      #5617898 - 01/11/13 07:59 PM

Here is thread for you to look at. thread
Watch for Jason's posts. I believe that you have a problem with your secondary mirror's position, looking at your photos.


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Starman1
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Reged: 06/24/03

Loc: Los Angeles
Re: Collimator concerns new [Re: NeilMac]
      #5617940 - 01/11/13 08:19 PM

Quote:

I went outside again to check the Collimator and it does look uniform.
I tried again to center it while the tube was horizontal then as i move the tube up the point also moved ??

I betcha its going to be a clear night tonight

Thanks for the vid coopman



That means your secondary spider vanes aren't tight enough.
If they're tight enough, you won't see the laser move on the primary as you change altitude.


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panhard
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Re: Collimator concerns new [Re: Starman1]
      #5618095 - 01/11/13 10:04 PM

Don it could be weak springs on the primary also. What do you say?

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Jeff2011
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Re: Collimator concerns new [Re: panhard]
      #5618225 - 01/11/13 11:37 PM

Neil,

I can sympathize with you. I had to finally adjust my secondary after moving my primary up to achieve prime focus. Took a long time of fiddling with it but I think I finally got it. I have a laser collimator similar to yours. I recommend using a Barlow with it. It is basically worthless without one. After laser collimating, double check your work with the pinhole cap they gave with the scope. If it does not look right then it's not right. I found that after I started using the Barlow, it looked right.


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NeilMac
Carpal Tunnel


Reged: 09/25/10

Loc: MedHat, AB, Canada
Re: Collimator concerns new [Re: panhard]
      #5618234 - 01/11/13 11:46 PM

Quote:

That means your secondary spider vanes aren't tight enough




So the screws on the tube?
My confusion is I can only adjust the allen keys one way and that is to loosen them, and that only moves the secondary a little moving them the other way Im afraid to brake something since the vanes will twist.
Will read the "Useful info about secondary mirror alignment" tomorrow, im just wiped.

Took out my 38mm for a test run and looks great. Was out not long since its -27c and fingers were going, took some pics but jiggley spots on the longer exposure.

Edited by NeilMac (01/11/13 11:47 PM)


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AutoPilot
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Reged: 12/14/12

Loc: S.E. Pennsylvania
Re: Collimator concerns new [Re: NeilMac]
      #5618250 - 01/11/13 11:57 PM

When collimating your scope there can be dozens of variables as this thread has revealed. My best collimation to date was after I tightened up the tolerances between the focuser and the 2” to 1.25” eye piece adapter and the tolerances between the 2” to 1.25” eye piece adapter and the laser collimator. If you leave the set screws lose on all of the “slip fits” you will find the laser point will move all over the mirror. And I mean all over! Tighten the set screws and the laser points moves again. I played with this for a minute or two and immediately knew that my collimation would never be where it needed to be.

To fix this I wrapped Scotch tape one layer at a time around each joint. If one layer didn’t take up the slop I went with a second. (Full wraps are required to keep everything centered on the same axis). Foil tape would be a better (cheap) long term solution. Once the slop is removed you have given yourself a fair shot at getting it right.

My next steps will be purchasing a Antares 2” to 1.25” Twist-Lock eye piece adapter to help keep things centered (replace the Scotch tape or foil tape), collimate my laser (if it needs it) and modify my laser to give me a smaller point (currently a fuzzy rectangle). Those mods should hold me over until my observing skills improve enough to where I need to take further steps.

I may try the barlowed method Don described to verify my collimation before and after.

If I understand Herb’s comment he means the springs that are between the OTA and the mirror mount. The springs allow the mirror to float into position which is then later locked into place when the set screws are tightened. Tightening the set screws themselves can throw you collimation off. If the springs are weak they may not be pushing the mirror into position when the set screws are loosened.

Also, the thumb screws that hold the spider (secondary mirror) in place should be checked for tightness. The secondary mirror should hold collimation when the OTA is horizontal, vertical or anywhere in between.


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Jeff2011
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Re: Collimator concerns new [Re: AutoPilot]
      #5618273 - 01/12/13 12:11 AM

I tried all the things autopilot suggested but in the end only the Barlow method worked for me. If your collimator has a target on it, you don't need to make the white disk on the bottom of the Barlow. Just use the target on the collimator instead.

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panhard
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Re: Collimator concerns new [Re: AutoPilot]
      #5618277 - 01/12/13 12:16 AM

Neil in order to move the secondary you have to loosen at least one of the 3 hex head screws to tighten another. That way you will walk the secondary into the proper position.

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Starman1
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Re: Collimator concerns new [Re: panhard]
      #5618352 - 01/12/13 01:08 AM

Quote:

Don it could be weak springs on the primary also. What do you say?



That scope has locking knobs in between the main collimation knobs. Once locked down, the cell can't move.
However, if the mirror were loose in the cell and tipped forward, it's possible for the laser to move on the primary.
But since 90% of the tubed dobs I've seen have had a too-loose spider, and since a too-loose spider causes the laser to move, if I were a betting man my money would be on a too-loose spider.


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Starman1
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Re: Collimator concerns new [Re: NeilMac]
      #5618359 - 01/12/13 01:13 AM

Quote:

Quote:

That means your secondary spider vanes aren't tight enough




So the screws on the tube?
My confusion is I can only adjust the allen keys one way and that is to loosen them, and that only moves the secondary a little moving them the other way Im afraid to brake something since the vanes will twist.
Will read the "Useful info about secondary mirror alignment" tomorrow, im just wiped.





Where the spider vanes are attached to the tube, there are bolts or nuts that can be tightened. When tightening, hold the vane inside the tube with your fingers so it doesn't twist.
The vanes should emit a high pitch if plucked--they need to be quite tight.

You see, when the scope points up, the secondary hangs under the spider. When the scope points low, the secondary is beside the spider and that weight imparts a twist to the spider vanes.
Want to test how sensitive that can be? Turn your laser on, reach inside the tube and just put a tiny amount of sideways pressure on the secondary holder and watch the laser move on the primary.
THAT'S why the spider has to be tight.


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lamplight
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Re: Collimator concerns new [Re: NeilMac]
      #5618631 - 01/12/13 09:07 AM

Quote:



My concern right now is the screws to adjust the Secondary mirror, their either tight or loose.
.




Hi Neil
I wonder if you're experiencing an issue I just had: after moving my secondary to center it in the focuser opening, I tightened the center screw way too much, this causing any micro adjustments of the 3 collimation knobs to have the same behavior you describe. I had to loosen it up a bit and let the spring work which lets the collimation knows work better in both directions if you know what I mean.

Once you get the secondary straightened out I definitely +1 for the barlowed method of adjusting primary. I just learned that here and it's easy!


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