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Equipment Discussions >> Reflectors

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Vic Menard
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Reged: 07/21/04

Loc: Bradenton, FL
How to Collimate your Newtonian
      #2193204 - 02/15/08 08:25 AM

I've already posted my "procedure" before, but I'll be happy to do it again. Still, I feel it's important to caution the user that it's possible, even with a systematic approach to alignment, to end up on what appears to be a "dead end." I sometimes find it's easier (and quicker!) to re-zero all of the mechanicals and start over...

I created this procedure for users with CatsEye tools and Glatter lasers, although it should work well for most scopes with a simple combo tool (and a properly aligned economy laser that has consistent registration with the focuser drawtube if one's available.) The final autocollimator procedures are useful for resolving any residual axial errors--but more importantly, the autocollimator teaches the end user to be more deliberate when completing each collimation step.

PRELIMINARY ADJUSTMENTS

1. Center the spider.
2. Check the focuser for perpendicularity to the tube axis.
3. Center spot the primary mirror (or verify the accuracy of the existing center spot.)

SIGHT TUBE AND LASER COLLIMATION

(I usually go back and forth with the TeleCat and the Glatter laser with the 1mm aperture stop for best precision.)

1. Position the sight tube in the focuser until the perimeter of the bottom edge appears slightly larger than the outer edge of the diagonal holder. Or, with a holographic laser, position the diagonal under the focuser until it appears centered in the holographic display.
2. Collimate the outer perimeter of the diagonal mirror with the bottom edge of the sight tube (or holographic pattern) by adjusting the axial and rotational alignment of the diagonal holder (and the focuser tilt, if necessary.)
3. Collimate the primary mirror spot with the intersection of the sight tube crosshairs by adjusting the tilt of the diagonal mirror. Or, with a simple point source laser or holographic laser, adjust the diagonal tilt to align the laser with the primary mirror center spot.
4. Check the tilt and coverage of the diagonal mirror with the reflected edge of the primary mirror. The primary mirror reflection appears concentric with the actual edge of the diagonal mirror and the mirror retaining clips are visible. Verify the rotation and angle alignment. Repeat steps 2 and 3 if necessary.
5. Collimate the reflection of the inside of the focuser (seen in the silhouetted reflection of the diagonal mirror) with the intersection of the sight tube crosshairs by adjusting the tilt of the primary mirror. Or, use the simple point source laser or holographic laser and collimate the return beam to the laser aperture.

(Or, if you're using the TeleCat, make sure that the primary mirror alignment is corrected to the precision of the calibrated Cheshire ring and triangular primary mirror center spot.)

(6. Fine tune the diagonal mirror tilt (focuser axial alignment) during regular observing sessions with the Glatter laser and 1mm aperture stop. The laser beam and its diffraction pattern facilitate the alignment with the triangular center spot perforation on the primary mirror.)

Proceed to the Cheshire or Barlowed laser next.

THE CHESHIRE EYEPIECE AND THE BARLOWED LASER

1. Fine collimate the primary mirror with the Cheshire eyepiece by adjusting the tilt of the primary mirror until the reflection of the primary mirror spot is observed centered in the reflected image of the Cheshire eyepiece. Or collimate the primary mirror to align the silhouetted center spot on the face of the Barlowed laser.

(2. Fine tune the primary mirror collimation during regular observing sessions with a diffuse red light to illuminate the Cheshire or use the Barlowed laser. Follow the procedure above.)

(Note that the Barlowed laser procedure is parallax free. This means the position of your eye relative to the optical axis has no impact on the read. Also note that if you're using the 1mm aperture stop with the Glatter laser, you can often see the silhouette of the triangular primary mirror center spot on the white target on the face of the laser, similar to a Barlowed laser protocol. This makes the Glatter laser with the 1mm aperture stop an after dark high precision combo tool of sorts, capable of assessing and correcting both axes!)

THE AUTOCOLLIMATOR

1. Begin by accurately collimating the telescope with the other tools.
2. Set up the telescope in a brightly lit room or outside environment or illuminate the primary center spot with a red flashlight at night.
3. With the autocollimator in the focuser, observe the reflected images of the primary center spot and using the iterative method, stack the reflections into a closer jumble (by adjusting the diagonal or the focuser), recollimate the primary mirror with the Cheshire or Barlowed laser, restack the reflections in the autocollimator by adjusting the diagonal or the focuser, recollimate the primary with the Cheshire... Continue to reiterate the procedure until the reflections are within tolerance or they disappear behind the primary mirror center spot.

or,

3b. Carefully decollimate the primary mirror. Adjust the diagonal or focuser to align the fainter, second inverted reflection with the primary mirror spot. Recollimate the primary mirror by stacking the remaining reflections until they disappear behind the primary mirror center spot.

4. Verify the primary mirror collimation with the Cheshire eyepiece or Barlowed laser and the focuser with a simple point source or holographic laser. All tools should agree.

Edited by Don W (02/15/08 04:27 PM)


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BozemanWalt
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Reged: 01/05/08

Loc: Bozeman, Montana
Re: Collimation Issue? new [Re: Vic Menard]
      #2193311 - 02/15/08 09:19 AM

Thanks for posting this Vic, much appreciated.

--Walt


Quote:

I've already posted my "procedure" before, but I'll be happy to do it again.




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backwoody
Pooh-Bah


Reged: 01/08/07

Loc: Idaho USA
Re: Collimation Issue? new [Re: BozemanWalt]
      #2193537 - 02/15/08 11:15 AM

Don, Jason, Alexis, and others:

I just wanted to express my thanks for this thread. I've studied Vic's book, Don Pensack's articles, and Alexis' posts about collimation, and still consider myself somewhat inexperienced in that department.

Extensive detail, semantics, or analysis of fairly obscure problems can still mystify me, leaving me temporarily dazed and confused - because of my relative inexperience compared to the experts. Nevertheless, my understanding has improved during this discussion.


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sixela
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: Collimation Issue? new [Re: backwoody]
      #2194015 - 02/15/08 03:18 PM

Quote:


Extensive detail, semantics, or analysis of fairly obscure problems can still mystify me, leaving me temporarily dazed and confused - because of my relative inexperience compared to the experts.




You can always ask questions. Of course, that has a tendency to derail the thread if it's someone else's (as should be clear from this thread), so you could post another thread. But then the original poster might not see something that is relevant, so choosing between posting it in an existing thread or in a new one is a call you can only make perfectly with hindsight .


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Don W
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Re: Collimation Issue? new [Re: sixela]
      #2194176 - 02/15/08 04:29 PM

Thank you very much, Vic. I want to thank Sixela and the others who have contributed to this subject here in the past. Good collimation makes such a great difference in observing.

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sixela
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: Collimation Issue? new [Re: Don W]
      #2195304 - 02/16/08 04:06 AM

I'll take a crack at an even shorter text for the procedure (not with the level of detail of Vic's though). To be as short as possible, I won't discuss the tools that let you do this, I'll just discuss what they aim to do.

1. Move the outline of the secondary¹ to be centred under the focuser (you can either physically move the secondary or tilt the focuser towards it; to pick a choice, see how centred the secondary looks from the front of the tube and see how easy it is to adjust the tilt on the focuser)

2. Rotate the secondary to make it appear as circular as possible

3. Tilt it to centre the primary centre spot reflection under the focuser, or to make a laser collimator's forward beam hit the primary's centre spot.

4. Go back to 1, until 1-3 no longer require you to do anything². Don't obsess - good enough is, so stop when you're fed up. 3. is most critical, and what follows is more critical.

5. Change the tilt on the primary.
5a. If you have a tool in the focuser with a centred pupil, make the reference (the pupil itself, or a bright Cheshire ring concentric with it) concentric with the primary centre spot reflection³.
5b. If you have a barlowed laser, centre the silhouette of the primary's centre spot in the returning light cylinder in the focuser opening.

6. Go back to 3. or 1., and repeat until you're fed up with it or no further adjustments are needed. Again, 5. is critical if you're getting too bogged down in the early steps; move along to 5. if you think the rest is good enough, but don't skip that step.

--
¹Don't confuse the outline of the secondary itself with the primary's reflection in it. Use coloured paper behind the secondary or between the secondary and the primary to make things more clear if necessary.
²The astute reader will have noticed that 1. and 3. together mean the reflection of the primary and the outline of the secondary will be concentric.
³The astute observer will see that the silhouette of the reflection of the secondary is actually not concentric, but offset along an imaginary line towards the primary. If the offset isn't on that line, you may have a small residual error in what you've done in steps 1. and 2., but it's your choice whether to ignore it or start again.


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backwoody
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Reged: 01/08/07

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Re: Collimation Issue? new [Re: sixela]
      #2195925 - 02/16/08 01:25 PM

Alexis, nice work. Thank you.

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Spaced
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Reged: 03/01/05

Loc: Tacoma, Washington, USA
Re: Collimation Issue? new [Re: backwoody]
      #2198127 - 02/17/08 01:39 PM

Vic, thanks for posting the Summary of all Summations. I'm glad it was permanently pinned to the forum.

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Almach
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Reged: 02/27/07

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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #2198138 - 02/17/08 01:42 PM

Quote:

2. Check the focuser for perpendicularity to the tube axis.




What is the best way to do the above?


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Vic Menard
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Loc: Bradenton, FL
Re: How to Collimate your Newtonian new [Re: Almach]
      #2198171 - 02/17/08 01:56 PM

Quote:

Quote:

2. Check the focuser for perpendicularity to the tube axis.



What is the best way to do the above?



I posted this quite a bit earlier (7/23/04 "Secondary Mirror Alignment", now in "The Best of Reflectors" thread.) There are, of course, other ways to align the mechanical focuser axis. And even though the focuser axis is the reference axis for optical collimation, this "mechanical" adjustment is really just a good starting point...

Procedure--
Step one. Measure the spider vanes from edge to center and from the four (or three) mounting points to the front edge of the tube. If the spider isn't properly centered or is mounted incorrectly and not parallel to the front of the OTA, make the necessary adjustments to make it all "textbook".

Step two. Remove the diagonal. Using a laser (or sight tube--but a laser is easier!), rack the focuser out far enough so that the focuser drawtube or the bottom of the laser doesn't protrude into the interior of the tube (front cage assy). Rotate the laser to verify that the laser spot on the opposite side of the tube from the focuser does not move. Insert a ruler from the front edge of the tube (cage) until it moves under the focuser and occults the laser beam. Take a measurement. Go to the opposite side of the tube (cage) and insert the ruler until the laser spot just moves entirely onto the ruler. This measurement should equal the previous measurement and indicates the focuser axis is correct longitudinally. If it's off more than about 3 to 5% of the minor axis of the diagonal, you should shim (or adjust) the focuser. Next, with the laser still in the focuser and the primary mirror uncovered, stand in front of the tube assembly and line up the actual spider with its reflection (in the primary mirror). Hold this position and place your hand with your palm facing you between the spider and the primary mirror. Look down the hole of the spider (where the diagonal holder is normally mounted) and notice the position of the laser spot. If it is high or low (about half the earlier tolerance), the focuser axis will need to be adjusted. This preliminary alignment procedure uses the optical/mechanical axis as the alignment guide for setting the pitch angle (as opposed to the intercept angle) of the focuser. This is only a starting point for focuser collimation and should not be considered "final" collimation for the focuser. A “squared focuser” is a good place to start--but other considerations may require additional adjustments.

Step three. Reset the diagonal adjustment screws to the "start" position (all screwed in equal amounts) so the rotational and angular adjustments of the diagonal can be set without additional skew errors. Visual inspection of the the diagonal back plate (push plate) and the adjusting screw plate should reveal roughly parallel surfaces. I've seen these get really screwed up when collimation is performed exclusively with a laser. If they are out of alignment, make the necessary adjustments to correct the mechanical condition. I also inspect the barrel that retains the diagonal mirror to verify that it is mounted flush and level to the back plate. Again, all “textbook”.

Reinstall the diagonal. Using a sight tube or Cheshire eyepiece (for shorter focal ratios), adjust the longitudinal positioning and rotation to center the diagonal under the focuser. If the diagonal can’t be properly centered without adjusting the three (or four) angle adjustment screws, the focuser should be shimmed to accomodate the centering process. Then you can set the diagonal angle adjustment with the laser or sight tube. Procede with primary mirror collimation (Cheshire or Barlowed laser) and fine tune as needed...


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JimMo
I'd Rather Do It Myself


Reged: 01/08/07

Loc: Under the SE Michigan lightdom...
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #2200595 - 02/18/08 02:54 PM

Thanks for the post Vic. I am already doing close to your procedure and it'll now be easy to fine tune it. I was only doing one iteration with the auto collimator and now I'll do a few more. Also, when stacking the triangles I was always confused when the refections disappeared and now I know they are supposed to. I don't have a 1mm aperture stop either and will call HG and see if I can get one.

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GaN
member


Reged: 06/05/05

Loc: Europe, Czech
Re: How to Collimate your Newtonian new [Re: JimMo]
      #2228460 - 03/01/08 12:17 AM

http://www.andysshotglass.com/Collimating.html

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Tull1996
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Reged: 07/07/08

Loc: Plattsburgh NY, USA
Re: How to Collimate your Newtonian new [Re: GaN]
      #2529802 - 07/20/08 10:20 AM

Wow, I hope this is a much easier process in practice than it is reading how! When I get my dob, I want to spend my time looking at the sky, not collimating the darned thing!

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Wobrak
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Reged: 04/18/08

Loc: SC, USA
Re: How to Collimate your Newtonian new [Re: Tull1996]
      #2529913 - 07/20/08 11:39 AM

With practice it is an easier process than it appears. It's the learning curve that makes seem as though you will spend the entire evening collimating instead of viewing.

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sixela
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Reged: 12/23/04

Loc: Boechout, Belgium
Re: How to Collimate your Newtonian new [Re: Tull1996]
      #2530916 - 07/20/08 09:42 PM

Quote:

Wow, I hope this is a much easier process in practice than it is reading how! When I get my dob, I want to spend my time looking at the sky, not collimating the darned thing!



You'll spend more time reading about it than you'll spend doing it (except perhaps the first time, when you place the secondary under the focuser).


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Mike Conley
professor emeritus
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Reged: 09/23/07

Loc: NW Ohio
Re: How to Collimate your Newtonian new [Re: sixela]
      #2531389 - 07/21/08 08:07 AM

Just picked up a custom truss tube.It's been some time since my last reflector ( Orion 8" Dob ). I had no trouble collimating the Orion, but this one is puzzling me. It has a 3 vain spider with bob knobs or something similar. I can place the howie glatter in the moonlight focuser and get a perfect return beam, center on the primary and return to dead center on the face of the laser. Good enough ? Well, when I place the collimation cap in the focuser, the reflection of the primary is off center to one side. I'm having to tilt my secondary for the laser alignment which is making the sighting through the cap out of alignment. Went back and forth about 6 times, same everytime ( I'm a hard head ). Tried realigning the secondary, loosening the center post and slightly turning to square to the face of the focuser, but it actually seems to need to go the opposite of square to show correct in the collimation cap. The only way I've been able to correct it was to tighten one adjutment screw on the spider while loosening the other two. I had to pull the spider to one side about 1/16 of an inch off center. I now have alignment both in the cap and with the laser. My question, does that sound right, shouldn't the secondary be dead center or as long as I can get the laser dead center both on the primary and on the return beam good?
Am I missing something or over thinking this?

Thanks Mike


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Vic Menard
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Reged: 07/21/04

Loc: Bradenton, FL
Re: How to Collimate your Newtonian new [Re: Mike Conley]
      #2531618 - 07/21/08 10:45 AM

Quote:

...My question, does that sound right, shouldn't the secondary be dead center or as long as I can get the laser dead center both on the primary and on the return beam good? Am I missing something or over thinking this?



When you collimate a Newtonian you are basically aligning three things (pretty much in this order):
First--the secondary mirror
Second--the focuser axis
Third--the primary mirror axis

Note that the focuser and primary mirror have axes, and the secondary mirror does not. The laser beam points wherever the focuser drawtube points, so it defines the focuser axis. Once the focuser axis is precisely aimed at the center of the primary mirror (usually accomplished by adjusting the secondary mirror tilt), the return beam can be used to align the primary mirror axis.

But wait--we forgot the first step, aligning, or centering the secondary mirror under the focuser. OK, so you use the collimation cap to center the actual edge of the secondary mirror relative to the bottom edge of the focuser (notice we're aligning circles, not axes). But then you adjust the secondary mirror again when you aim the laser at the center of the primary mirror (focuser axis alignment)--which messes up the secondary mirror alignment you just did with the collimation cap!

The goal, of course, is to get both alignments corrected simultaneously. Unfortunately, most folks use secondary mirror tilt to fix both, and end up going back and forth undoing the alignment of the other! The secret is to use secondary mirror tilt to fix one (laser), and rotation and/or movement toward or away from the primary mirror to fix the other (collimation cap.) This way, after a couple of tries, you will soon resolve both alignment errors.

Re: secondary mirror appearing "dead center". If the actual edge of the secondary mirror is centered relative to the bottom edge of the focuser drawtube, the dark silhouette reflection of the secondary mirror will NOT appear centered in the reflection of the primary mirror, but will instead appear offset towards the primary mirror end of the OTA. This is how the finished secondary mirror alignment should look. (If the dark silhouette reflection of the secondary mirror appears centered in the reflection of the primary mirror--the actual edge of the secondary mirror will NOT appear centered relative to the bottom edge of the focuser drawtube, but will instead appear offset away from the primary mirror end of the OTA. This secondary mirror alignment still works, but it doesn't provide optimal illumination at the focal plane.)


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Mike Conley
professor emeritus
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Reged: 09/23/07

Loc: NW Ohio
Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #2531855 - 07/21/08 12:56 PM

Vic,
Thanks for the reply. My secondary mirror appears round when looking through the collimation cap, the mirror is centered in the focuser tube. I can see the secondary holder also, but the mirror itself appears round and centered. I thought that was the goal. I then used the tilt feature so that the primary was centered and I could see all three clips and centered it. After that I used the laser and made slight adjustments. So your saying I may have it off? Should I start from scratch. I wasn't comfortable moving the spider adjustments, but tried rotating the secondary holder and raising /lowering it, but could not keep everything centered as I thought that was the goal. I'll keep reading, maybe purchase the hologram attachment for the laser would help with the secondary placement?

Thanks Mike


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

Loc: Madison, AL USA
Re: How to Collimate your Newtonian new [Re: Mike Conley]
      #2537341 - 07/23/08 07:22 PM

Before you get too far down the investigative path with Vic's guidance, let's don't forget validating the internal collimation of the laser by rotating it 360 dgrees in the focuser against the drawtube lip and observe the beam spot on the Primary... the spot must remain stationary through 1 complete rotation in a collimated laser. If it "orbits" significantly, all bets are off.

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travvy
member


Reged: 12/13/07

Loc: Tillsonburg, Ontario
Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #2537821 - 07/24/08 12:04 AM

Mike, I have the same problem with my orion classic 8, but being a newbie. I realized that i never knew the secondary could travel in and out a bit... so this maybe my problem. the andyshotglass is a great movie to watch and learn.

Good luck


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Mike Conley
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Reged: 09/23/07

Loc: NW Ohio
Re: How to Collimate your Newtonian new [Re: travvy]
      #2540172 - 07/25/08 08:14 AM

Thanks Guys. I ordered a cheshire and positioned the secondary ( it was off ), followed by the single beam laser ( it is collimated, rotated it in the focuser ) . The laser confirmed the chesire and just needs to be star tested now.

Mike


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DanJ
Pooh-Bah


Reged: 12/01/04

Loc: Knoxville, TN
Re: How to Collimate your Newtonian new [Re: Mike Conley]
      #2550351 - 07/30/08 12:53 PM

I "believe" my scope is collimated pretty good, star tests and etc, but this thread is tempting me to go out and see if some of the above is on the mark....HELP
You folks are so tempting

Cheers!


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FirstSight
Duke of Deneb
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Reged: 12/26/05

Loc: Raleigh, NC
Re: How to Collimate your Newtonian new [Re: DanJ]
      #2550453 - 07/30/08 01:47 PM

One of the trickier aspects of Newtonian collimation is that turning the adjustment screws for either the secondary or the primary mirror does *not* produce a neat, linear movement of the aligment, but rather somewhat of a curving arc. And so, e.g. when the primary center-spot is off-center directly above where it should be, turning any of the knobs will cause it to move not just up or down, but also cause it to deflect a bit to the right or left as well. Likewise, when the primary center-spot is off-center to the left or right, turning any of the knobs will cause it to move not just left or right, but a bit upward or downward as well. Again, the movement is never along a linear path, but more along the sort of arc that might be produced by drawing with a compass centered where the knobs are, with the pencil where the center spot is. Regardless of the kind of tools you're using to do the collimation with, this inescapable aspect of using a system of three adjustments symmetrically spaced around a circle can be a bit maddeningly nonintuitive, especially as you draw progressively closer, but not yet adequately spot-on during the procedure. Especially those laaaast irresistible attempts to nudge the triangle dead-center from just a small tinch up or down (or right or left).

It does help (if you are using a triangular reflective center spot) to set the mirror in its cell such that either the points of the triangle, or else the centerpoint of each triangle edge, are aligned with each respective collimation knob. This gives you a much better sense of cause-and-effect of turning each knob than if the triangle alignment had no easily visible correspondence with the collimation knobs.

Edited by FirstSight (07/30/08 02:01 PM)


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Paulin
journeyman


Reged: 05/08/08

Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #2664984 - 09/26/08 04:17 PM

Hello everybody. I bought an 6.5" Maksutov-Newtonian and I would like to know if the instructions by Vic about collimation can be applied for my telescope in a general way. In fact I want to know first if my telescope is collimated or not.

Thank you in advance
Regards
Paul


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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: Paulin]
      #2665446 - 09/26/08 09:47 PM

Quote:

I bought an 6.5" Maksutov-Newtonian and I would like to know if the instructions by Vic about collimation can be applied for my telescope in a general way.



Yes.

Quote:

In fact I want to know first if my telescope is collimated or not.



Have you tried to evaluate the optical performance with a star test yet? If you suspect that the collimation is incorrect, do you have access to any collimation tools?


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Paulin
journeyman


Reged: 05/08/08

Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #2666917 - 09/27/08 09:23 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


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Vic Menard
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Reged: 07/21/04

Loc: Bradenton, FL
Re: How to Collimate your Newtonian new [Re: Paulin]
      #2667949 - 09/28/08 01:01 PM

Quote:

...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.)


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Paulin
journeyman


Reged: 05/08/08

Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #2670743 - 09/29/08 06:57 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


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Re: How to Collimate your Newtonian new [Re: Paulin]
      #2683092 - 10/06/08 10:00 AM

Quote:

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.cloudynights.com/item.php?item_id=1548

Quote:

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.

Quote:

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.

Quote:

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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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #2741807 - 11/08/08 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

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Re: How to Collimate your Newtonian new [Re: Timber]
      #2742085 - 11/08/08 11:54 PM

Quote:

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,


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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #2742992 - 11/09/08 03:09 PM

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

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Re: How to Collimate your Newtonian new [Re: Timber]
      #2743034 - 11/09/08 03:45 PM

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

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Re: How to Collimate your Newtonian new [Re: Don W]
      #2788012 - 12/05/08 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


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Re: How to Collimate your Newtonian new [Re: travvy]
      #3021657 - 04/03/09 10:10 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


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Re: How to Collimate your Newtonian new [Re: jayw65]
      #3272525 - 08/14/09 02:23 PM

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

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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3425604 - 11/02/09 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.



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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Re: How to Collimate your Newtonian new [Re: RedIrocZ-28]
      #3425718 - 11/02/09 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!


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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3425821 - 11/02/09 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.


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Re: How to Collimate your Newtonian new [Re: RedIrocZ-28]
      #3425854 - 11/02/09 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?


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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Re: How to Collimate your Newtonian new [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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Re: How to Collimate your Newtonian new [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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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3975413 - 08/10/10 06:50 PM

Quote:

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.




Basically, I can see the full reflection of the primary (i.e. all four mirror clips), and I have centered the reflection of the peephole in the middle of centermark on the primary. This adjustment has already given me views at first light that are better than anything my SCTs have ever given me, but I would like to know what additional adjustments might be useful.

I am not really sure how each axis is named. As far as I can tell, the possible adjustments of the secondary are rotation (does the secondary appear circular instead of oval), position along the central OTA axis (i.e. is the outline of the secondary centered in the peephole), and tilt (is the primary fully visible and reasonably centered in FoV of the secondary). Am I missing anything? Any thoughts on this?


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Re: How to Collimate your Newtonian new [Re: uniondrone]
      #3976378 - 08/11/10 09:09 AM

Quote:

...I can see the full reflection of the primary (i.e. all four mirror clips), and I have centered the reflection of the peephole in the middle of centermark on the primary.



The first part ("I can see the full reflection of the primary...") means you should have good illumination across the fov. The second part, ("I have centered the...peephole in the middle of the center mark..."), means you have good primary mirror axial alignment.

Quote:

I am not really sure how each axis is named.



There are only two. I think you already understand the primary mirror axis and how to correct it (you described it above). Correcting the primary mirror axis places the "sweet spot" in the center of the fov. It's the most critical alignment, requiring corrections less than a few hundredths of an inch for an f/5 primary mirror. Thankfully, aligning the collimation cap pupil to the primary mirror center spot (donut) is pretty easy, and the pupil/center spot alignment actually magnifies any residual primary mirror axial error 2X.

The other axis is the focuser axis. It's easy to recognize if you have a simple thin beam laser collimator. With the laser mounted in the focuser, the beam is the focuser axis. The focuser axial alignment tolerance for a 10-inch aperture (w/o Paracorr) is about three tenths of an inch (more than 10X the tolerance of the primary mirror) measured relative to the primary mirror center spot. Generally speaking, the most common way to correct the focuser axial alignment is to tilt the secondary mirror to aim the laser beam at the primary mirror center spot. If you don't have a laser, you can get similar results using a sight tube and aligning the crosshairs to the primary mirror center spot.

Quote:

As far as I can tell, the possible adjustments of the secondary are rotation (does the secondary appear circular instead of oval), position along the central OTA axis (i.e. is the outline of the secondary centered in the peephole), and tilt (is the primary fully visible and reasonably centered in FoV of the secondary). Am I missing anything?



Yep. The secondary mirror alignments you've described above should get the focuser axial alignment close. But are you close enough? Three tenths of an inch sounds like a lot, but using your alignment procedure, you'll need to either perfectly center the secondary mirror relative to the bottom edge of the focuser drawtube, or split the tolerance between the two alignments (bottom edge of focuser to actual edge of the secondary, and actual edge of the secondary to the reflected edge of the primary). That's only one and a half percent of the apparent diameters--a pretty tough read. It's doable--but it's a lot easier with the right tool.

FWIW, exceeding the focuser axial tolerance causes the focal plane to tilt enough to begin to impact image performance. Lower magnifications and eyepieces with less edge correction minimize the impact. If you're getting "snap" focus with your current alignment and you're satisfied with your scope's performance, I wouldn't worry too much about it.


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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3976669 - 08/11/10 11:43 AM


Hi Vic, Thanks for the detailed reply. It all makes good sense to me now.

One more question: how critical is the order of the adjustments? I have already aligned the cap pupil with the primary center spot. Presumably if this was done with poor secondary alignment (i.e. tilt adjustment), then the primary axis is actually aligned with a misaligned secondary. Oddly enough, conversely, aligning the focuser axis by centering the crosshair of an alignment EP with the centerspot of a misaligned primary would result in a secondary that is aligned with poorly aligned primary. It seems like a chicken and egg situation.


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Re: How to Collimate your Newtonian new [Re: uniondrone]
      #3976854 - 08/11/10 01:09 PM

Quote:

...how critical is the order of the adjustments?...It seems like a chicken and egg situation.



The order of axial alignment is simple: first, focuser axis, last, primary mirror axis. This is because, as you noted in your post, adjustments to the focuser axis typically impact the primary mirror axial alignment--but adjustments to the primary mirror axis usually have little or no impact on the focuser axial alignment.

Getting the secondary mirror positioning fully corrected and achieving good focuser axial alignment simultaneously can seem like a "chicken and egg situation" if the alignments are not approached systematically. I won't go into detail here because it's already covered on the first page of this thread.

But remember to always correct/tweak the primary mirror axial alignment last!


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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3977262 - 08/11/10 04:18 PM


Thanks again, Vic! As batty as all this probably drives some people, I am really starting to appreciate the degree of control and ability for DIY that a Dobsonian provides.


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Re: How to Collimate your Newtonian new [Re: uniondrone]
      #3978857 - 08/12/10 01:16 PM


Hi Vic,

I tried using a laser collimator, but found that the loose tolerances of the fit in the focuser creates a lot of room for error. A slight wobble in the collimater gives a movement of as much as two inches for the laser reflection on the primary. The laser striking the target on the collimator can pretty much move across the entire field with a slight wiggle. Tightening it down with the set screw shows the primary to be *way* out of alignment, despite the fact that I can visually confirm good alignment using the peephole in the collimation cap.

Any advice?


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Re: How to Collimate your Newtonian new [Re: uniondrone]
      #3979158 - 08/12/10 03:56 PM

Quote:

...I tried using a laser collimator, but found that the loose tolerances of the fit in the focuser creates...error...as much as two inches for the laser reflection on the primary.

Any advice?



Sure. First, I hope the loose fit is caused by the laser and not the focuser, because if it's the focuser, your eyepieces will be subjected to the same focuser axial misalignment--not good. Now, if it's the laser's fault (and it usually is), and the fit is really that bad, the best option, IMO, is to replace the laser. Some users advocate taping the laser barrel to get a tighter fit, but what you really need is a barrel that mimics an eyepiece barrel, that way when you secure the laser in the focuser, it's axis mimics an eyepiece's axis. I also suspect you're using a 2-inch focuser, with a 2- to 1.25-inch adapter, and a 1.25-inch laser. A better 2- to 1.25-inch adapter should improve the fit and the alignment consistency. How the eyepiece fits the adapter, and how the adapter fits the focuser drawtube, is called "registration". It's important to verify the focuser axial alignment with the locking screws secured, the same way you would use the locking screws with an eyepiece. This "fixes" the registration. If the misalignment is repeatably consistent when the locking screws are secured, your focuser axis is indeed, misaligned!

If you have a dial caliper or similar measuring tool, you can quickly determine the cause of your registration inconsistency.

Quote:

...Tightening it down with the set screw shows the primary to be *way* out of alignment, despite the fact that I can visually confirm good alignment using the peephole in the collimation cap.



"Tightening it down" only secures the registration of the laser to the focuser. Remember, the laser beam defines the focuser axis. The return beam is simply a reflection of the focuser axis. The only way the return beam can be used for primary mirror axial alignment is if the focuser axial alignment is perfect. One half of any residual focuser axial error will be propagated forward to the laser beam emitter. I'm guessing this is what you're seeing when you say the primary is "*way* out of alignment". The collimation cap, which is relatively insensitive to focuser axial errors, shows the primary mirror alignment is in fact, "good", so you're back to where you started: good secondary mirror positioning, good primary mirror axial alignment, and unknown focuser axial alignment.

Of course, even without a laser, we know your focuser axis isn't grossly misaligned, even though it may be out of tolerance. As long as you're happy with your scope's performance, you shouldn't lose good observing hours worrying about what might be wrong. Learning how to collimate your scope is all about patience and persistence, an exercise best saved for rainy days and cloudy nights (pardon the pun).

Edited by Vic Menard (08/12/10 04:04 PM)


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uniondrone
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #3979249 - 08/12/10 04:45 PM


Vic, thanks for the advice!

You are correct that the telescope has a 2" focuser with a 1.25" adapter. I will use my calipers to measure the outside barrel of the laser collimator and inside of the adapter to see how much play is there. I do have a higher quality adapter that came with my SCT Crayford. I could try using that instead. The focuser on the Dob is the stock rack and pinion focuser used in older model Orion Dobs.

I totally agree with you on the part about not worrying too much as long as the performance makes me happy. So far it has met or exceeded my expectations. My main aims are 1) to at least have a competent understanding of all major aspects of collimation, and 2) have all adjustments close enough to tolerance to know that my view is not significantly compromised.

You mentioned using a crosshair alignment tool for aligning the secondary. Although I imagine that it would be susceptible to the same registration issues, it might actually be easier to line it up with the center spot of the already aligned primary than trying to get the laser to work. Any thoughts on this? Is there any advantage in doing this, or is it just going to give the same problem?


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Vic Menard
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Re: How to Collimate your Newtonian new [Re: uniondrone]
      #3979371 - 08/12/10 05:57 PM

Quote:

...using a crosshair alignment tool...I imagine that it would be susceptible to the same registration issues, it might actually be easier to line it up with the center spot of the already aligned primary than trying to get the laser to work. Any thoughts on this?



IME, a good laser is easier to use than a good sight tube when you're aligning the focuser axis. And you can use the laser as effectively after dark. But I still like a good sight tube for positioning the secondary mirror.

Quote:

My main aims are 1) to at least have a competent understanding of all major aspects of collimation, and 2) have all adjustments close enough to tolerance to know that my view is not significantly compromised.





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kev721
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4018979 - 09/01/10 12:17 AM

Has anyone tried the $44 laser collimator from scopestuff? It looks the same as the ones that cost $69 and up from other shops.

Please let me know if anyone has tried it.

Thanks!

Scope stuff laser collimator


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SonOfDob
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Re: How to Collimate your Newtonian new [Re: kev721]
      #4221098 - 12/01/10 01:35 PM

My god,... I think you guys spend more money on collimation equipment than I did on my entire 10" start to finish,... granted the price of glass has gone up

Seriously though,... put a dot in the middle of the mirror, line the secondary up so you see the same amount of tube on all sides when looking down the eyepeice (position yourself 6-12" back from the eyepiece tube and you can use the inner and outer openings to align your point of view), then adjust the mirror so the center dot lines up in the middle of the properly positioned secondary.

Plywood, cardboard, elmers glue, a throwaway pair of binoculars, a few inches of plumbing pipe, teflon tacks, a lag bolt and a bit of scrap leather is about all you need to build as big a damn reflector as you can find glass to grind.

A 24" dobsonian has been made start to finish in 2 days by 2 guys ,... I just wish you could still buy US navy surpluss porthole glass in bulk!


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Jason D
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Re: How to Collimate your Newtonian new [Re: SonOfDob]
      #4221141 - 12/01/10 01:51 PM

Quote:

My god,... I think you guys spend more money on collimation equipment than I did on my entire 10" start to finish,... granted the price of glass has gone up

Seriously though,... put a dot in the middle of the mirror, line the secondary up so you see the same amount of tube on all sides when looking down the eyepeice (position yourself 6-12" back from the eyepiece tube and you can use the inner and outer openings to align your point of view), then adjust the mirror so the center dot lines up in the middle of the properly positioned secondary.

Plywood, cardboard, elmers glue, a throwaway pair of binoculars, a few inches of plumbing pipe, teflon tacks, a lag bolt and a bit of scrap leather is about all you need to build as big a damn reflector as you can find glass to grind.

A 24" dobsonian has been made start to finish in 2 days by 2 guys ,... I just wish you could still buy US navy surpluss porthole glass in bulk!




Why don't you start a new thread with your thoughts.


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SonOfDob
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #4221229 - 12/01/10 02:27 PM

Sure,.. Why not

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Jan Owen
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4332718 - 01/22/11 06:39 PM

At THIS stage along the way, anything *I* might say is relatively meaningless.

But still, I've been in amateur astronomy for about 45 years now, more or less (probably more, since it really dates back to the late 1940's when my dad showed me a lunar eclipse through HIS telescope, given to him by his dad).

I've been using my own telescopes for a LONG time, starting with the ubiquitous 60mm department store refractor, and working up to 24", then after massive back problems, back down to 12" and less...

My only reason in pointing that out, is that, in those years, my BIGGEST take-away has been that there are THREE things that are critical for optimum viewing (assuming quality optics, of course). Seeing, telescope thermal equilibration, and collimation.

NONE of these can be under-estimated in their importance. But only TWO are directly under OUR control. Thermal equilibration, and collimation...

Vic (and several cohorts) has done the whole family of amateur astronomy a LOT of good by putting what needs to be done, and how to DO it, down on [virtual]paper, and making it readily available here (and on their Yahoo Group)...

I've learned a LOT from Vic and friends over the years, above and beyond decades of personal experience, and just wanted to take a few minutes here to thank THEM!!!


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CollinofAlabama
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4530006 - 04/19/11 06:53 PM

With all due respect to Nils Olaf Carlin, Vic Menard, and Don Pensack, I'm sorry, but all your writings have been like Polish to me (and I know no Slavic tongue -- da [or duh, in my case]). Every time I started reading one of your texts, my eyes would glaze over, and in my mind an inner demon would whisper "you know, with a refractor, you don't have to worry about all this"

But then I remembered to google YouTube, where pictures (at 24 frames a second) are indeed worth a thousand words (tens of thousands when the subject is collimation). Ladies and gentlemen, the absolute best collimation guide for the collimation-averse ...

http://www.youtube.com/watch?v=yd3mjOr8rc0&feature=youtube_gdata_player

Now, you need some kind of cheapo laser collimator to utilize this, but most folks with a reflector these days have one. If you don't go buy one for $50 and you're in business (or, as the Canuck says in the video, pay more for a "quality" laser collimator). He uses a cheapy, and mine, the Orion Deluxe Collimator, is probably considered cheapy, too. I don't care. Collimation finally makes sense and is EASY.

"Free at last, free at last. Thank God Almighty ..." Well, you know the rest.


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Jason D
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Re: How to Collimate your Newtonian new [Re: CollinofAlabama]
      #4530098 - 04/19/11 07:45 PM

If you are happy with that video and would like to share it with others, that is absolutely fine.
However, your words about Vic, Nils Olof, and Don were completely unnecessary – especially in a sticky thread. If you find their writing confusing, many others find the same writing helpful.
By the way, that video does not cover other aspects of good collimation such as how to optimally position the secondary mirror under the focuser.
If you want to discuss, I suggest starting a new thread. Leave this one alone.
Jason


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Vic Menard
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Re: How to Collimate your Newtonian new [Re: CollinofAlabama]
      #4530215 - 04/19/11 08:34 PM

Collin,
I watched the youtube video you've described as "the absolute best collimation guide for the collimation-averse". The procedure is similar to the one I use with my scope when assessing and correcting the focuser and primary mirror axial alignments. I use a better laser with my procedure because I need better precision for my f/4 coma corrected Newtonian's axial alignments.

An economy laser may be sufficient for a longer focal ratio optic--ymmv. Of course, if you only use the procedure as demonstrated in the youtube video, it's quite likely the secondary mirror will soon need additional help. If you read through the last few posts in this thread (just page 4 should be enough), that's more or less what we've been discussing.

Finally, I don't speak any Slavik tongues either, but I do recognize that sometimes, trying to actually understand collimation principles can cause one's eyes to "glaze over" and having to deal with the often less than precision alignment mechanisms found in many economy Dobsonians can cause one's teeth to gnash and one's hands to wring. Id est quod id est.

To close, I think this quote by Albert Einstein is appropriate, "Make everything as simple as possible, but not simpler."

Edited by Vic Menard (04/20/11 06:51 AM)


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fender2547886
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4531557 - 04/20/11 12:54 PM

Hi Everyone,
I own the new at 12" f4 reflector and am beginning to love it. But I have a question.
1-I collimate the tube with it is a horizontal position.
2-I use the Orion deluxe collimator.
3-I have the laser pointed dead center on the mirror.
4-I have the return beam of the laser perfectly aligned on the primary mirror.
5-But when I leave the laser on and move the sope to a more vertical position the return laser beam from the primary is shifted and is not centered no longer on the center hole on the Orion Laser Collimator.
6-I did add washers to the outside of the spider since the spider nuts where too short .
7-everything is locked down.
8-Is this normal or is the primary shifting?
I would love some input.
Danny


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hiddenwolf
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Re: How to Collimate your Newtonian new [Re: fender2547886]
      #4532222 - 04/20/11 05:20 PM

you want to collimate your scope with the ota level with the horizon so on its side. also rotate the laser in the focuser and watch the beam on your primary and see if it stays motionless , if it wobbles then your laser is out of collimation. also check for slop in your focuser tube clamp.

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nheacock
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Re: How to Collimate your Newtonian new [Re: hiddenwolf]
      #4532313 - 04/20/11 05:54 PM

Generally speaking, that's good advice, but I can tell you that if I collimate my 16" Meade Lightbridge when it's level I'd see nothing in collimation because as soon as I raise it 20 degrees or so it's out again. This is because of shift in the primary and slop in the overall design of the trusses.

I always collimate at 50 or 60 degrees or so altitude (which of course means exceedingly careful handling of the tools).

If I stick my laser in the focuser and move the scope in altitude, the dot moves on the primary. Not because the laser is out of collimation, but because of the play in the system. Danny is likely experiencing some form of this as well.

It's not uncommon for large Newts (Truss Dobs in particular, though Danny didn't mention what form of reflector he's got) to have collimation shift at different altitudes. In my case, the Meade Lightbridge in particular is more severe then what I've seen on others, either ATM or commercial. I'd say from personal experience of looking through dozens of Dobs ranging from 12" to 40" that I've never seen one hold perfect collimation at all altitudes (with rigid, high tension string Dobs performing the best).

So my advice to someone who has this problem is to collimate in the middle of your typical viewing altitude and you'll go out the least at either extreme.

-Neil


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Jason D
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Re: How to Collimate your Newtonian new [Re: nheacock]
      #4535477 - 04/21/11 10:10 PM

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4531553/page/0/view/collapsed/sb/5/o/all/fpart/1

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Tesselator
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4639237 - 06/14/11 08:02 PM

Quote:

I've already posted my "procedure" before, but I'll be happy to do it again.




Thanks! I recently investigated collimation myself too. I recently added a Vixen Super Polaris R-130-S to my scope collection (of 2 ). This is my first reflector. It's a Newtonian telescope... what a neat names you cosmologists come up with. I almost feel like in owning one of these I'll now be able to command gravity or something. I guess I got a good deal on it (??) $50 for the scope, 3 eyepieces, a motor driven mount that seems to weigh several tons, and some fairly sturdy legs. Anyway, being me, I had to find out everything I could about it and found out that these types of scopes occasionally need to be Collimated. Not having any idea what Collimation was nor what skills and tools were involved I began searching. After reading just about every tutorial and watching just about every video I finally came across a guy making a little sense! Yay for making sense!!! So here's a playlist and the nine parts!

Playlist: YouTube - Broadcast Yourself.


Embeded videos:

Part 1:
YouTube - ‪Newtonian Collimation Part 1‬‏

Part 2:
YouTube - ‪Newtonian Collimation Part 2‬‏

Part 3:
YouTube - ‪Newtonian Collimation Part 3‬‏

Part 4:
YouTube - ‪Newtonian Collimation Part 4‬‏

Part 5:
YouTube - ‪Newtonian Collimation Part 5‬‏

Part 6:
YouTube - ‪Newtonian Collimation Part 6‬‏

Part 7:
YouTube - ‪Newtonian Collimation Part 7‬‏

Part 8:
YouTube - ‪Newtonian Collimation Part 8‬‏

Part 9:
YouTube - ‪Newtonian Collimation Part 9‬‏



Whew! Well worth the watch tho however you choose to view it - either automatically in series at the playlist link or by clicking on the individual parts.


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Jason D
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Re: How to Collimate your Newtonian new [Re: Tesselator]
      #4639486 - 06/14/11 10:46 PM

Sorry, but that is NOT the best collimation series out there.
9 videos and the guy does not even cover how to align the focuser axis by redirecting the laser beam to the primary center. In fact, he talks against it. This guy does not understand collimation well. He is mixing focuser axial alignment with secondary mirror positioning. These are different alignments but he thinks they are the same. Interestingly, he has Vic's book as shown in the video. Maybe he should spend little more time reading that book to improve his understanding of the collimation theory.
Furthermore, he collimates the primary while the OTA is in a horizontal position -- not a good idea.
Jason


Edited by Jason D (06/15/11 12:46 AM)


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Twilight
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #4639661 - 06/15/11 01:53 AM

I would love to see Vic Menard, Jim Fly and Howie Glatter put together a video on CD for sale for about 20.00 to 25.00 bucks with the complete procedure like in Vic's book. I don't know if it could be done for 25.00 but it sure would get my buy after reading Vic's book. The video would be worth lets say 2500 words. Come on guy's I know you can do it. It would be a best seller for astronomy! Let me see here. $25.00 times 100,000 copy's. That would be a good starting point.

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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4790735 - 09/05/11 04:09 PM

Hello All,

I refer back to the very last sentence of Vic's original post that "All tools should agree". Therein lies my problem. I've had my new Orion XT10g goto Dob for a little less than two months and have been very happy with the performance so far. But this is my first experience with a reflector and so am concerned that I can and do collimate the scope well, which I've read is especially important in a fast f4.7 scope. When I first got the scope, I used the included collimation cap and after reading the instruction manual carefully, achieved what I consider to be good collimation verified by a star test at first light. Maybe I should've left well enough alone but being obsessed with collimation, I bought a good quality laser collimator, the kind with a side window for ease of collimating from the primary end. I do recall when I first used the laser collimator, it seemed like I had to do quite a bit of adjustment from what I had achieved just using the collimation cap. I just chalked it up to that the original collimation was off from moving the scope in and out of the house several times. Then I learned about barlowed collimation for the primary and have been using that technique before each of the past two to three observing sessions. Again star tests seem to indicate that the scope was in good collimation.

But then just today (told you I was obsessed ) I decided to check the collimation. I put in the collimation cap, which I hadn't used since the first couple of collimations and much to my surprise, the collimation seemed to be significantly off. It appeared that the secondary was centered well but the primary was not very centered in the secondary (in fact, one of the four mirror retaining clips wasn't even visible) plus the primary center donut was off center as well. So I went ahead and re-collimated (first secondary then primary mirrors) using the collimation cap then inserted the laser collimater in the focuser and saw that it was out of collimation - the laser was about a quarter to half an inch off of the primary center donut and the return laser was off center on the side window to about the first concentric circle from the center spot. I went through collimation again by centering the laser on the primary center donut, put in the barlow and centering the donut shadow in the side window.

Well if you haven't been too bored and have read this far, you can guess what happened next. I removed all the laser and barlow stuff and put the collimation cap back in and again the collimation was well off. Frustrating to say the least. I've read elsewhere about laser collimators being out of collimation so I clamped a wood quarter round piece of molding in a workbench, put the laser collimator in it and slowly turned the laser while watching the laser on a white wall about six feet away. The point seemed to pretty much stay in one spot.

Star testing under both collimation techniques produce good results but how could the two techniques be so far off from each other? Any idea what I'm doing wrong??


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Vic Menard
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Re: How to Collimate your Newtonian new [Re: Tiebreaker]
      #4790847 - 09/05/11 05:05 PM

Let's start with "star testing". To precisely verify the primary mirror axial alignment on a star, you'll need to keep the star carefully centered and use a magnification of about 250X or more, defocusing the star just enough so you can see a few diffraction rings (if you can see the silhouette of the spider in the defocused star, you've defocused too much). Assuming the primary mirror center spot is well placed on the primary mirror surface, the Barlowed laser and/or the collimation cap should deliver a good star test. You can verify both of these primary mirror alignment tools by simply rotating them in the focuser drawtube--resecuring the locking screw each time before you read the alignment. Both tools should easily reveal errors in the alignment read as small as 0.02-inch, and since both tools magnify the actual primary mirror axial error 2X, you should be able to correct the primary mirror axial error to a precision of 0.01-inch.

The unBarlowed thin beam laser is useful when aligning the focuser axis. Although you usually adjust the secondary mirror tilt to aim the laser at the primary mirror center spot--you are actually aligning the focuser axis. Many users believe they are actually aligning the secondary mirror, but you can quickly prove to yourself what's really happening by either rotating the secondary mirror or adjusting it closer to or further from the primary mirror. No matter what you do to the secondary mirror placement, you can always adjust the tilt screws to align the focuser axis with a thin beam laser.

The confusion then is how do you properly place (rotation and fore and aft adjustments) the secondary mirror under the focuser so the three alignments (primary mirror and focuser axes and secondary mirror placement) are all corrected simultaneously? The answer lies in separating the axial adjustments (the axial lines that define the primary mirror and focuser axes--or the centers of the circles) from the secondary mirror alignment (the edges of the circles).

The first adjustment is always secondary mirror alignment. This involves aligning three circles--the bottom edge of the focuser drawtube, the actual edge of the secondary mirror, and the reflected edge of the primary mirror. Assuming the secondary mirror is reasonably centered in the OTA and the focuser is reasonably "squared" to the OTA, you can optimally place the secondary mirror by adjusting its rotation, fore and aft position, and relative tilt. When the three circles are concentric, the primary mirror center spot should also be almost perfectly centered, which leads to the second, focuser axial adjustment. After you've tweaked the focuser axial alignment with the thin beam laser, you need to make the third, and final, primary mirror adjustment with the collimation cap. Always make the adjustments in the sequence described. If you go back to tweak the focuser axial alignment, always finish with a precise primary mirror alignment.

I suspect the discrepancy between the various reads is related to the tools you're using. While the collimation cap does a good job aligning the primary mirror, it's not the best tool for optimally placing the secondary mirror. Even a small error (+/-0.1-inch or 1-percent of the primary mirror reflection diameter) is an obvious error when using a thin beam laser to align the focuser axis. I also suggest verifying the thin beam laser accuracy in the focuser by rotating (and resecuring the locking screw between reads) the laser and observing the position of the beam relative to the primary mirror center spot. Without a Paracorr, this alignment can be +/-0.3-inch, but I prefer to verify the laser to at least +/-0.1-inch (with a Paracorr, the tolerance is reduced to +/-0.05-inch).

Barlowing a side window laser is OK for coarse primary mirror alignment, but I suggest following this coarse alignment with your collimation cap (which should also be verified through various rotated positions in the focuser drawtube). If the collimation cap consistently agrees with the side window Barlowed laser (within +/-0.02-inch), you can probably skip the final tweak with the collimation cap. If the two tools differ significantly, even if it's 80-percent hit, 20-percent miss, you should always finish with the verified collimation cap.


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mwtse
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #4862091 - 10/15/11 09:20 AM Attachment (93 downloads)

I find that the secondary mirror is not positioned at the center of the spider, should I center the spider or offset the spider so that the mirror is centered in the optical tube?

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mwtse
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Re: How to Collimate your Newtonian new [Re: mwtse]
      #4862122 - 10/15/11 09:55 AM

I've found the answer:

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4222723/page/0/view/collapsed/sb/5/o/all/fpart/all/vc/1


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sixela
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Re: How to Collimate your Newtonian new [Re: mwtse]
      #4862529 - 10/15/11 01:52 PM

The answer is that the attachment was meant to implement a centred holder and spider and an offset diagonal -- just to be sure you jumped to the right conclusion.

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dodgerm37
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5069409 - 02/12/12 06:52 PM

Does anyone have "RECENT" instructions for the Zhumell Z-10? After assembly I'm trying to check collimation on a new Z-10. Instead of the screws mentioned in instructions, mine has three white knobs and three black knobs. Has anyone run into this situation? HELP!! The skys might clear in the next few months. Thanks

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Jason D
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Re: How to Collimate your Newtonian new [Re: dodgerm37]
      #5069497 - 02/12/12 07:52 PM

I suggest starting a new thread with your question.

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NickS
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5079681 - 02/19/12 07:44 AM

Hi I'm a very new astronomer and the mirror thing worries me quite a bit. I'm fine with the process of alignmet. But is there an issue of getting the primary mirror to focus it's magnified image at an exact spot on the secondary? If that is the case, then how is that achieved?

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Jason D
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Re: How to Collimate your Newtonian new [Re: NickS]
      #5079921 - 02/19/12 10:47 AM

Can you start a new thread with your questions? Do clarify your question. It is unclear what you meant by "getting the primary mirror to focus it's magnified image at an exact spot on the secondary."

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Joe_C
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #5232811 - 05/21/12 04:44 PM

I have a (relatively) inexpensive Dob: Zhumell Z12. I have collimated using a combination Celestron cheshire / sight tube, following (as far as possible with the tools at hand) the "Collimation And the Newtonian Telescope V4" writeup by Donald E Pensak at www.cloudynights.com/item.php?item_id=2677.
The results have been less that spectacular for viewing, even at 300X magnification:
Mars - I see the planet, but no detail
Jupiter - I see three moons, no planet detail
Saturn - I see two rings, no planet detail

I'm pretty sure that collimation is the issue, and have some questions related to this:

1. Is this scope and its Crayford focuser of good enough quality to purchase and use the Catseye system of collimation products?

2. I would like to remove the primary and check / replace the center spot, but (being new to this hobby) I am quite nervous about removing the primary. I looked at: http://www.cloudynights.com/ubbarchive/showflat.php/Cat/0/Number/1552280/page/0/view/collapsed/sb/1/o/all/fpart/1. Since I will be doing this alone, I would rather not have the tube standing upright on the floor. I would like to leave it in its "cradle", and (somehow) support the primary as I remove the screws. Any help / thoughts on accomplishing this would be greatly appreciated.


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Husbyggarn
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Re: How to Collimate your Newtonian new [Re: Joe_C]
      #5233553 - 05/22/12 03:25 AM

I also used a Cheshire/sight tube but was never satisfied with the views i was getting, i always suspected the collimation was not correct.
Finally i bought a laser collimator and a 2x barlow. I payed about 100$ for both.
First i use the laser without barlow to center the laser dot on the primary mirror center marking by adjusting the secondary mirror and looking down the telescope. When that is ok i use the laser with the barlow, and now since the laser beam is wider i get a reflection of the whole primary mirror doughnut center marking on the lasers collimator's tilted viewing screen, now i center the reflection by adjusting the primary mirror.
I always do this before every viewing session and it takes about 5 minutes now.
Then i know that the scope is working at optimum so i don't have to worry about that.
Well worth the investment and the time.
Oh, and wait about 30 mins to let the mirror cool down before doing serious observations.


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Joe_C
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Re: How to Collimate your Newtonian new [Re: Husbyggarn]
      #5233698 - 05/22/12 08:15 AM

After reviewing Astro Baby's "A Simple Guide to Collimating a Newtonian Reflector" writeup: http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm
I'm beginning to think that I may have a scope with damaged optics.

The airey disk I see in Intrafocus and Extrafocus looks very much like his last image of an "Optical Surface Damaged - defocused". There are no concentric "rings", just outward-radiating ring-like "spikes". They are interesting / almost beautiful to look at, but certainly not "rings" as seen in the other images.

Any suggestions about how I might take a picture of one through my (Dobsonian) eyepiece, so that I can post it here online to show what I am seeing?


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Husbyggarn
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Re: How to Collimate your Newtonian new [Re: Joe_C]
      #5236020 - 05/23/12 04:24 PM

I don't think your optics is damaged, it may just be atmospheric turbulence.
You may have to look for a while to catch those moments when the atmosphere is steady.

IMHO, I would advise you to invest in a laser collimator and barlow. Then you can atleast narrow the issue down when the scope is properly collimated.


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JoeM101
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Re: How to Collimate your Newtonian new [Re: Husbyggarn]
      #5255014 - 06/04/12 05:09 PM

I have a question for Vic, I also have an f/4 scope, mine with a Baader MPCC (multi purpose coma correcter), when collimating, do I take the MPCC out or can it be done with it in?? What difference does it make if any and what is the recommendation for faster coma corrected scopes?

One more thing, if i may...
I have to say that reading Vic's thread(s), JasonD, sixela, and Nils, have opened my eyes a little wider with regards to collimation. Though at times the esoteric eludes me, all in all, they have given us the very best and most detailed explanations imaginable and i for one am absolutely thrilled that these people put in the time to share with all of us their vast collective knowledge and experiences. i'm getting better at collimation, slowly but surely and understand more than ever, though i have to say, if anyone is interested in watching a video on collimation, this guy (Dion) isn't so bad Advanced Newtonian Collimation he has a way about him.. fun to watch! It may be a tad simplistic , but i think you will enjoy it, for what it's worth, not the best but offers a different prespective although doesn;t cover all the points.
Anyhow, armed with the knowledge gained on CN, with kudos to Vic, Jason , Nils , sixela, and last but not least Howie Glatter, compliment your skills... while looking at differing methods and perspectives. the more you learn, the the easier collimation gets, since the whole process has a bit of a learning curve involved.

keep an open mind but most of all open eyes

clear skies!!!


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Jason D
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Re: How to Collimate your Newtonian new [Re: JoeM101]
      #5255964 - 06/05/12 10:41 AM

Hello Joe,

Thank you for the kind words.

Quote:

if anyone is interested in watching a video on collimation, this guy (Dion) isn't so bad Advanced Newtonian Collimation he has a way about him




Unfortunately, references to the above video have been popping up in various forums. It is unfortunate because Dion makes a serious misleading claim. He discredits laser collimators by stating that laser collimators “lie.” Dion made the mistake of expecting laser collimators to be used to center/round the secondary mirror under the focuser. Unless a laser collimator is used with a holographic attachment, it is not expected to center/round the secondary mirror under the focuser.

Jason


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JoeM101
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #5256093 - 06/05/12 12:40 PM

Quote:

Hello Joe,

Thank you for the kind words.

Quote:

if anyone is interested in watching a video on collimation, this guy (Dion) isn't so bad Advanced Newtonian Collimation he has a way about him




Unfortunately, references to the above video have been popping up in various forums. It is unfortunate because Dion makes a serious misleading claim. He discredits laser collimators by stating that laser collimators “lie.” Dion made the mistake of expecting laser collimators to be used to center/round the secondary mirror under the focuser. Unless a laser collimator is used with a holographic attachment, it is not expected to center/round the secondary mirror under the focuser.

Jason




Jason, i agree that he goes a little far with regards to laser collimation in saying that they lie, hence my comment that it's a tad simplistic and doesn;t cover all the points. He does say that the laser is not intended to line up your secondary though, even though with a holographic attachment, as you stated, you certainly can... but anyhow, i wanted to see if you or any of the others, Vic? Nils?, Alexis (sixela).. would have a gander at a thread i started with regards to using a coma correcter while collimating and give some feedback as Howie has stated you guys (ray-tracers lol) were probably able to give some insight

The thread: Help Collimating an F/4 with coma correction

Since Vic is also using a coma corrected F/4, he may be able to shed some more light on this

thanks


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Re: How to Collimate your Newtonian new [Re: JoeM101]
      #5258096 - 06/06/12 11:58 AM

Quote:

I have a question for Vic, I also have an f/4 scope, mine with a Baader MPCC (multi purpose coma correcter), when collimating, do I take the MPCC out or can it be done with it in?? What difference does it make if any and what is the recommendation for faster coma corrected scopes?



I use a Paracorr2 with my f/4 scope. I always remove the Paracorr before I align the scope. I've verified my original Paracorr1 alignment (it's a weak Barlow) with my regular alignment and there was no change in the critical primary mirror alignment. I haven't actually checked the Paracorr2 yet, but I expect to find similar results as the scope's optical performance is excellent.

I can't tell you how the MPCC will behave, but if it does change the scope's axial alignments and you can't resolve the error (e.g., different threaded positions, different adapters, etc.)--and the error impacts the scope's performance--I would have it replaced.

Visual and imaging applications will place different demands on the axial alignments and the mechanicals. The smaller aperture astrographs can be difficult if you're pushing the performance envelope.


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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5258259 - 06/06/12 12:58 PM

Quote:

Quote:

I have a question for Vic, I also have an f/4 scope, mine with a Baader MPCC (multi purpose coma correcter), when collimating, do I take the MPCC out or can it be done with it in?? What difference does it make if any and what is the recommendation for faster coma corrected scopes?



I use a Paracorr2 with my f/4 scope. I always remove the Paracorr before I align the scope. I've verified my original Paracorr1 alignment (it's a weak Barlow) with my regular alignment and there was no change in the critical primary mirror alignment. I haven't actually checked the Paracorr2 yet, but I expect to find similar results as the scope's optical performance is excellent.

I can't tell you how the MPCC will behave, but if it does change the scope's axial alignments and you can't resolve the error (e.g., different threaded positions, different adapters, etc.)--and the error impacts the scope's performance--I would have it replaced.

Visual and imaging applications will place different demands on the axial alignments and the mechanicals. The smaller aperture astrographs can be difficult if you're pushing the performance envelope.




Thanks Vic,

I will try collimating with both Catseye tools and the Howie Glatter combo, then pop in the MPCC and keep my fingers crossed that nothing changes with the laser... hopefully they don't, the Baader only costs 180 as opposed to 500 for the TV.

clear skies


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fender2547886
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Re: How to Collimate your Newtonian new [Re: JoeM101]
      #5271216 - 06/14/12 12:53 PM

I have a question for the group. I have an AT 12.5" Imaging newtonian and am using a hutech sca laser collimator.
1-I sent the laser on the primary by adjustung the secondary screws.
2-I then adjust the primary mirror by adjusting the three screws at mirror cell.
3-I then double check the centering of the primary and everything is perfect until....


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fender2547886
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Re: How to Collimate your Newtonian new [Re: JoeM101]
      #5271230 - 06/14/12 12:58 PM

I have a question for the group. I have an AT 12.5" Imaging newtonian and am using a hutech sca laser collimator.
The scope is mounted on a Parallax hd150 mount with the OTA pointing about 10 degrees off the horizon. The focuser is a large format Moonlite bolted and reinforced with steel washers on the inside to keep it firmly secured. The laser collimator is seated squarely in the focuser and tightened in place.

1-I center the laser on the primary by adjusting the secondary screws.

2-I then adjust the primary mirror by adjusting the three screws at mirror cell.

3-I then double check the centering of the primary and everything is perfect until....

4-I leave the laser collimator on and untouched in teh focuser and move the scope from 10 degrees off the horizon to 20, 25, 30 60 degrees and I can watch the laser collimation move from dead center on the collimator to completely off the collimator!

I have tightened the secondary and there seems to be no loose parts. Any help? or Am I being too critical?


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mwtse
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Re: How to Collimate your Newtonian new [Re: fender2547886]
      #5271744 - 06/14/12 06:45 PM

Is most likely due to bending/twisting of varies part of your scope structure. Usually, the spider which support your secondary is made of the thinest metal so it is the first thing to look at. Look at the dot on the primary, if that dot drifted at different point angle of your scope (up and down), that usually means you have to tighten the secondary mounting screw more so that the spider is under tension. But be care that your OTA tube can withstand the great force.

For my scope, the red dot at primary mirror drifted for about 5 mm maximum, when I adjust the secondary screw again so that the red dot is back to centre on the primary after moving the scope up or down, the collimation was back to centre, that means the primary mirror of my scope is more or less not moving. But your scope may be different.


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De Lorme
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5296662 - 06/30/12 05:02 PM

Hi, I need some help in collimating my 10" AT f/3.9 reflector. I centered the secondry under the focuser. Next I
Used the 3 outer screws to center the primary tabs into the secondary mirror. Last I centered the Primary using the primary ajusting nobs to the secomndary mirror. When I put the cross hair chelshire into the focuser the cross hairs do not line up with centered primary. I can center the secondary to the cross hair and than center the primary to the cross hair but when I do there's ony 2 tabs in the field of view. Am I getting the full use of the mirror when I do it this way. Is it better to just center the 3 tabs and then center the primary{with it's ajusting nob's}, and then do a star test? Thanks for your advice. De Lorme


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JoeM101
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Re: How to Collimate your Newtonian new [Re: De Lorme]
      #5296669 - 06/30/12 05:07 PM

Good question, i had a similar issue, could only see 2 of the three primary tabs when collimated with both HG laser and catseye tools. Jim from catseye said i need to realign my secondary... sold the scope but still curious as i'm waiting on a dob now and would like to know in case i run into the same issue on the new scope

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ManojK
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Re: How to Collimate your Newtonian new [Re: JoeM101]
      #5325158 - 07/19/12 02:25 PM Attachment (94 downloads)

Hey guys, this has probably be answered in this long thread, but I am looking for some pointed advice. I have an Orion f/4 8" newtonian that I use for astrophotos. The collimation has always been the hardest part for me. Currently I have a Hotech 2" self centering laser, 1.25" collimation cap and a 1.25" crosshair sight tube. Centering the secondary in the focuser tends to be very hard for me because the sight tube does not show the whole secondary regardless of the position in the focuser. Would the collimation cap with the focuser racked in all the way work for this purpose? Even then is it just subjective visual estimation or are there tools that will quantitatively tell me if the secondary is centered to the focuser. Would the secondary centering actually affect collimation or just the illumination point on the chip (not centered)? Given the tools I have would it be worthwhile for me to invest in the catseyecollimation set of tools (they are pricey at 300 for all 3) and would they aid me better with the centering of the secondary and aligning the two axes?

The problem is worse because after collimation I use a MPCC in the train and I can't figure out whether the problems are because of the spacing between the MPCC and CCD or because of collimation or both. I have attached a 60s capture so you can evaluate how far off I am (either in terms of collimation or the spacing)


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TopHouse
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Re: How to Collimate your Newtonian new [Re: JoeM101]
      #5347444 - 08/01/12 06:15 PM

Quote:

Quote:

Hello Joe,

Thank you for the kind words.

Quote:

if anyone is interested in watching a video on collimation, this guy (Dion) isn't so bad Advanced Newtonian Collimation he has a way about him




Unfortunately, references to the above video have been popping up in various forums. It is unfortunate because Dion makes a serious misleading claim. He discredits laser collimators by stating that laser collimators “lie.” Dion made the mistake of expecting laser collimators to be used to center/round the secondary mirror under the focuser. Unless a laser collimator is used with a holographic attachment, it is not expected to center/round the secondary mirror under the focuser.

Jason




Jason, i agree that he goes a little far with regards to laser collimation in saying that they lie, hence my comment that it's a tad simplistic and doesn;t cover all the points. He does say that the laser is not intended to line up your secondary though, even though with a holographic attachment, as you stated, you certainly can... but anyhow, i wanted to see if you or any of the others, Vic? Nils?, Alexis (sixela).. would have a gander at a thread i started with regards to using a coma correcter while collimating and give some feedback as Howie has stated you guys (ray-tracers lol) were probably able to give some insight

The thread: Help Collimating an F/4 with coma correction

Since Vic is also using a coma corrected F/4, he may be able to shed some more light on this

thanks




As the person in question, it seems Jason makes a habit of circulating around various forums making claims that I make misleading statements and various other derogatory claims. Since he chose to do this in public forums, and since he did not see fit to pass comment on the available youtube messaging facility or indeed through my own site, I feel it is only fair that in retrospect, I be allowed to defend myself in the same medium.

The simple fact is that the instructions for almost every single point laser collimator on the market give a procedure for centering the secondary that involves adjusting rotation and the tilt/skew grub screws to center the single point in the middle of the donut on primary. This is WRONG and I stated as such, using this method, a rotation can be apparently corrected using a skew adjustment. Therefore, the single point laser, when used for secondary adjustment in this way LIES!

Strange that in a number of his derogatory attacks on myself in various forums have also resulted in him contradicting himself!

So apparently, according to Jason, what I said was wrong, yet he states in many posts that a single point laser is not the tool for centering a secondary! Hmmmm, go figure!

Apologies to the mods for this, but you allowed the slurs to be posted on the forum so it is only fair that I have the right of redress.

I do have personal issues with Jason and we have had our run in's before, however I don't go around slurring him on public forums, and I do feel that an amount of this is down to this 'personal issue'. So Jason, if you want to have a pop, please feel free to do it to may face, directed 'at' me as opposed to on public forums. This is my last word on the matter on this forum.

regards,

Dion

http://www.astronomyshed.co.uk


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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: TopHouse]
      #5347680 - 08/01/12 08:51 PM

Quote:

...The simple fact is that the instructions for almost every single point laser collimator on the market give a procedure for centering the secondary that involves adjusting rotation and the tilt/skew grub screws to center the single point in the middle of the donut on primary. This is WRONG and I stated as such, using this method, a rotation can be apparently corrected using a skew adjustment. Therefore, the single point laser, when used for secondary adjustment in this way LIES!..





Hi Dion,

I suspect there is a conflict of semantics at play here. In most CN forum discussions about the adjustments of the Secondary, there are three distintly different collimation phases and referencing terminologies:

1) "CENTERING" of the Secondary is the process of making the necessary adjustments (via the central stalk and spider vane attachments and/or focuser base relocation/shims) in a plane perpendicular to the focuser axis to center the Secondary directly beneath the focuser to symetrically capture the image light cone. A simple "beam' laser most certainly WILL NOT aid in this endeavor; the sight tube or "holographic pattern" laser are the tools to use.

2) "PRESENTATION" optimization involves the process of adjusting the tilt and rotation of the Secondary to eliminate Secondary "skew" and facilitate as near a circular projection of the elliptical surface to the focuser as possible. A simple "beam' laser most certainly WILL NOT aid in this endeavor; the sight tube or "holographic pattern" laser are the tools to use. There is only 1 combination of Secondary tilt and rotation that will be optimum for presentation.

3) "AXIAL ALIGNMENT" of the Secondary is the process of adusting the tilt/rotation of the Secondary to aim the focuser axis at the center of the Primary. A beam laser or cross-hair sight tube WILL facilitate this. There are an infinite number of combinations of Secondary tilt and rotation settings that will achieve focuser axis alignment. In this regard, unless the beam laser is itself internally out of alignment, regardless of the centering and presentation condition, it does not "lie" - it clearly demonstrates an accurate response to a selection of one of those setting combinations. If the beam strikes the center of the center spot, a coarse axial alignment has been accomplished and it's usefulness stops there.

The bottom line is that focuser axial alignment CAN be achieved irregardless of the state of "centering" & "presentation" condition of the Secondary, but that said, it's prudent to implement centering and proper presentation, BEFORE focuser axial alignment is undertaken.

If there are indeed beam-laser instructions out there that infer Secondary "centering" (and/or "presentaton") can be accomplished with that tool, it's the procedure writer who is mis-informing the user, not the laser.


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Jason D
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Re: How to Collimate your Newtonian new [Re: TopHouse]
      #5347859 - 08/01/12 10:41 PM

For the record, I only criticized your misleading message in my replies to others who innocently tried to perpetuate your misleading message about how laser collimators “lie”. I never made an attempt to start a thread or start a subject criticizing your video – I only replied to other posts and I will continue to do so. My participation in several forums pre-dates your video and has nothing to do with you. I do stand by what I stated about your misleading message and by my opinion of your collimation expertise – lack of.

Quote:

The simple fact is that the instructions for almost every single point laser collimator on the market give a procedure for centering the secondary that involves adjusting rotation and the tilt/skew grub screws to center the single point in the middle of the donut on primary. This is WRONG and I stated as such, using this method, a rotation can be apparently corrected using a skew adjustment. Therefore, the single point laser, when used for secondary adjustment in this way LIES!



You do not seem to understand the difference between focal plane tilt adjustment and the 100% illumination field optimization adjustment. Both adjustments are made exclusively by the secondary mirror. Quality single laser collimators eliminate focal plane tilt error. They are not meant for optimizing the 100% illumination field. However, a laser collimator with a holographic attachment is capable of optimizing the 100% illumination field. An introduction of a small secondary mirror rotational error can be compensated for by a secondary mirror tilt error to eliminate focal plane tilt error – not the 100% illumination field error. That is what you have demonstrated in your video. In your video, you were only interested in optimizing the 100% illumination field. Here is an animation that I put together years ago. In each frame, the single laser beam hits the primary center then bounces back to the source. That is, each frame eliminates the secondary focal tilt error but only one frame eliminates the 100% illumination field error.


You can’t continue making misleading claims about single laser collimators. They do not “lie”. They are not meant for the 100% illumination field optimization. This is an old fact that has been communicated by Vic Menard and others for years. You did not make any new discoveries. You just took a known fact about single laser collimators then repackaged it as a new discovery under the misleading “laser lie” title.

Jason


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Jason D
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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5347862 - 08/01/12 10:42 PM

Quote:

If there are indeed beam-laser instructions out there that infer Secondary "centering" (and/or "presentaton") can be accomplished with that tool, it's the procedure writer who is mis-informing the user, not the laser.




Well-said, Jim


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TopHouse
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #5348249 - 08/02/12 07:15 AM

Quote:


You can’t continue making misleading claims about single laser collimators. They do not “lie”. They are not meant for the 100% illumination field optimization. This is an old fact that has been communicated by Vic Menard and others for years. You did not make any new discoveries. You just took a known fact about single laser collimators then repackaged it as a new discovery under the misleading “laser lie” title.

Jason




That would be the contradictions I'm talking about! Apparently I'm now claiming new discoveries as well! As I said Jason, you want to take it up with me in private, feel free!

Dion


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Jason D
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Re: How to Collimate your Newtonian new [Re: TopHouse]
      #5348445 - 08/02/12 10:10 AM

Quote:

you want to take it up with me in private




Dion, you are clearly taking this matter way too personal. Lighten up. I have no interest in pursuing this in private. As I have stated, I never started a thread or a subject criticizing your video. I only provided a fair balance whenever others tried to perpetuate your misleading claim. I believe I am entitled to post replies to other posts expressing my opinion and I will continue to do so. If you disagree with my replies, you are also entitled to reply to my posts in this forum and others to express your opinion. As long as we stay on the subject, I do not mind debating it.

Many beginners who watch your video will avoid purchasing single laser collimators because you told them that these tools “lie”. This is unfair. Quality laser collimators when used properly are excellent collimation tools and easy to use. Why couldn’t you explain the proper use of single laser collimators by clarifying that they are not meant for centering/rounding the secondary mirror under the focuser? That is it. Why did you use the word “lie”? The issue is not with the tool but rather with the improper usage of the tool.

Jason


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David PavlichAdministrator
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5348558 - 08/02/12 11:24 AM

OK, gang...let's get back on topic.

David


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Vic Menard
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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5348574 - 08/02/12 11:34 AM

Quote:

...The simple fact is that the instructions...(are)...WRONG. Therefore, the single point laser, when used for secondary adjustment in this way LIES!...



I don't think anyone will argue the point that the instructions provided with some economy laser collimators are often so simplified that the user will be hard pressed to achieve a reliable collimation. Check the one-step alignment procedure in the product description here.

I think the problem is the conclusion that the laser somehow "lies". Used properly, the outgoing beam of a simple thin beam laser represents one thing--the focuser axis. As the focuser axis is one of the two axes that will be assessed and corrected when collimating a Newtonian, and it's one of the two alignments that have a defined performance tolerance, it's an important axial alignment. If the internal laser alignment is good and the laser/focuser registration is consistent, there's no way the laser can "lie"--the outgoing beam is the focuser axis.

Many users also adjust the primary mirror tilt to align the return beam back to the laser target (often visible in a side "window"). But the return beam is simply the reflection of the focuser axis! If the focuser axis isn't precisely aligned to the center of the primary mirror first, using the return beam to adjust the primary mirror tilt will misalign the critical axial collimation.

A precision thin beam laser collimator coupled with precision mechanicals and used properly is a valuable tool for axial alignment assessment and correction.

Quote:

I suspect there is a conflict of semantics at play here.



Yep.

Quote:

1) "CENTERING" of the Secondary...(and)...2) "PRESENTATION" optimization...A simple "beam' laser most certainly WILL NOT aid in this endeavor; the sight tube or "holographic pattern" laser are the tools to use.



While I agree with this statement (and prefer a good sight tube for the job), there are still some users (and at least one manufacturer) who suggest using a secondary mirror reference spot to facilitate the alignment of the front end geometry with a simple thin beam laser. There are many pitfalls, complicated measurements, and convoluted "dead ends" associated with the procedure, but it has its following.

Quote:

3) "AXIAL ALIGNMENT" of the Secondary is the process of adusting the tilt/rotation of the Secondary to aim the focuser axis at the center of the Primary...



Again, semantics--the secondary mirror is an optical flat and has no axis--although it reflects both axes when assessing and correcting the axial alignment. As described, the alignment is "AXIAL ALIGNMENT" of the Focuser...

Since secondary mirror adjustments affect both axes, changing the focuser axis this way also changes the primary mirror axis, which is why primary mirror axial alignment is always the last step.

Quote:

The bottom line is that focuser axial alignment CAN be achieved irregardless of the state of "centering" & "presentation" condition of the Secondary, but that said, it's prudent to implement centering and proper presentation, BEFORE focuser axial alignment is undertaken.





Quote:

If there are indeed beam-laser instructions out there that infer Secondary "centering" (and/or "presentaton") can be accomplished with that tool, it's the procedure writer who is mis-informing the user, not the laser.



Although their numbers are dwindling, there are still advocates--some use a secondary mirror reference spot, some don't...

This exchange reminds me of a quote by Wolfgang Pauli (after reading a young physicist's paper):

"This isn't right, this isn't even wrong."


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Nils Olof Carlin
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5348920 - 08/02/12 03:44 PM

One crucial aspect of collimation is knowing what each tool will show, and what it won't show - in order to use the right tool to see what you need to know at any step.

Having decided that your primary center spot is centered accurately enough, as is your spider, a good first step is to use a peephole tool (any kind - just to give a centered perspective) and turn your secondary until it looks correctly rotated, and leave it there (checking later that it remains so!). Then tilt it to get at least somewhat close to the right tilt (laser, crosshairs sight tube - if not, the next step can be misleading). Next check the placement (in-out the tube, sideways) and correct if necessary (sight tube, combination tool, holographic laser - in a pinch, you can always later check that the primary and secondary are concentric) - if you need to adjust, repeat the sequence.
Now you can fine-adjust the tilt of the secondary (laser, crosshairs sight tube, autocollimator CDP), before last step (=tilting the primary). It is this step that Dion just omits (should have been described at the end of video 8, or beginning of 9, I believe), claiming that the (narrow-beam) laser isn't useful. It is indeed perfectly good, once the rotation of the secondary is known to be correct (and that is what I understand to be the gist of Jason's criticism).

It is easy to verify the shape and outline of the fully illuminated field (I have described how in a previous thread) - if circular (or possibly elongated or compressed along the tube - but not obliquely!), the rotation is OK.

Though not nearly as critical as the primary's axis, the focuser axis (adjusted by tilting the secondary) should be reasonably close - not to confuse the subsequent collimation of the primary, if for no other reason.

BTW, the video #9 well illustrates the potential problems of putting a side-window laser into a Barlow - we have discussed it in earlier threads. The reflection of the laser in the concave lens of the Barlow gives a quite bright spot on the center of the laser face, possibly large and bright enough (as shown) to confuse the reading of the spot's perforation shadow. Also, we mentioned the potential offset mechanism due to the diverging shadow. This may not be serious, but turning the laser 180 deg ought to reveal any significant problem here, I should believe.

Nils Olof


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S. Fritts
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5384440 - 08/24/12 11:57 AM

I am new at this and it is way too complicated for me. Could someone post a simple explaination for this procedure or am I out of my element even being here?

Steve


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Starman1
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Re: How to Collimate your Newtonian new [Re: S. Fritts]
      #5385197 - 08/24/12 08:24 PM

Quote:

I am new at this and it is way too complicated for me. Could someone post a simple explanation for this procedure or am I out of my element even being here?

Steve


Send me a private message with your email and I'll send you my tutorial.
Just bear in mind there are only a few steps:
1) move secondary up or down in the tube until it's centered under the focuser (doesn't have to be perfect). Don't do again until you remove the mirror for cleaning.
2) rotate the focuser around its center axis until it appears round to the eye (doesn't have to be exact).
3) Adjust tilt of secondary until centermarker on primary lines up behind crosshairs or until a laser points directly at the center of the primary's center marker. Be as exact as you can.
4) Adjust tilt of primary until image of center marker on the primary is in the center of a cheshire or centered around the hole in the bottom of a barlowed laser. Be as perfect as you possibly can be. This one is the most critical adjustment.

Though explanations can get a lot more long winded, that's about it. If an autocollimator tool is used, there is a fifth step, but it is pretty much refining the adjustments made in steps 2-4.
It helps to see illustrations of what you'll see with the tools, so send me that message.


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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: S. Fritts]
      #5385878 - 08/25/12 06:50 AM

Quote:

I am new at this and it is way too complicated for me. Could someone post a simple explaination for this procedure or am I out of my element even being here?

Steve




7 Steps for Perfect Collimation


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vman69au
journeyman


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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5389167 - 08/27/12 04:21 AM

Hello,

Hoping someone may be able to help me.

I just took possession on my first reflecting telescope ( an f3.8 Orion Optics AG-10). Have been a refractor guy for a while now.

I have the cats-eye collimation tools. The Telecat XLS site tube/Cheshire cobo and the infinity XLK collimator. ( one with central and offset pupil)

I have watched videos and followed instructions. I think I am reasonably close. Quite a learning curve I must say having never dealt with reflecting optics before.

Where I am at is as follows:

With the auto-collimator, looking through the center hole the hot dots are perfectly aligned. I then look through the offset hole each pair are not be perfectly aligned. If I get them perfectly aligned in the offset hole, they're not in the center hole.

To say another way, my radiation hotspot is centered in Cheshire and stacks are aligned in central view. Problem is in offset view they are not stacked . Once I adjust secondary to stack in offset view they are no longer stacked in central view and vice versa.

If I stack either central or offset with primary centered in Cheshire, my glatter laser puts laser dead center of the radiation spot.

I am just not sure why I cannot get offset AND central views to stack as per images and instructions. I have iterated back and forth between Cheshire for primary and Auto Collimator for secondary heaps of times.

Any suggestions what may be causing this and what I need to adjust ?


Thanks
Chris


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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: vman69au]
      #5389260 - 08/27/12 07:17 AM

Quote:

Hello,

Hoping someone may be able to help me.

I just took possession on my first reflecting telescope ( an f3.8 Orion Optics AG-10). Have been a refractor guy for a while now.

I have the cats-eye collimation tools. The Telecat XLS site tube/Cheshire cobo and the infinity XLK collimator. ( one with central and offset pupil)

I have watched videos and followed instructions. I think I am reasonably close. Quite a learning curve I must say having never dealt with reflecting optics before.

Where I am at is as follows:

With the auto-collimator, looking through the center hole the hot dots are perfectly aligned. I then look through the offset hole each pair are not be perfectly aligned. If I get them perfectly aligned in the offset hole, they're not in the center hole.

To say another way, my radiation hotspot is centered in Cheshire and stacks are aligned in central view. Problem is in offset view they are not stacked . Once I adjust secondary to stack in offset view they are no longer stacked in central view and vice versa.

If I stack either central or offset with primary centered in Cheshire, my glatter laser puts laser dead center of the radiation spot.

I am just not sure why I cannot get offset AND central views to stack as per images and instructions. I have iterated back and forth between Cheshire for primary and Auto Collimator for secondary heaps of times.

Any suggestions what may be causing this and what I need to adjust ?


Thanks
Chris




Chris,

Typically imaging telescopes (with coma correctors removed for collimating) have a natural focal plane 1.5" to 2" above the focuser. For the autocollimator to perform accurately and consistently, its mirror must be at or near the focal plane; as such, I suspect you are experiencing reflection queue parallax registration error. Get yourself a 2" focuser Barrel Extender to place between the focuser drawtube and the autocollimator and see if that helps.

This CN forum discussion may also be of interest to you: Custom XLK; if so, contact me at flyj@catseyecollimation.com .


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Jason D
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Re: How to Collimate your Newtonian new [Re: vman69au]
      #5389572 - 08/27/12 11:22 AM

Quote:

With the auto-collimator, looking through the center hole the hot dots are perfectly aligned.



Do reflections P & 2 have similar size or is one larger than the other?
When collimation is reached, you are not suppose to see a stack via the central pupil but rather a solo center spot -- unless the AC mirror is greater than 5% focal length below the focal plane.
Jason


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vman69au
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #5390904 - 08/28/12 06:15 AM

Jason, reflection 2 was MUCH larger, by nearly 40% I could hardly make out 3 and could not see 4.

I used a 2" eyepiece extension tube tonight which lifted the autocollimator about 70mm higher than from where it was.

Amazing the difference. The hot spot reflections were crisp and focused and looked just like the picture on the catseye website. I was able to get the offset view with double stacked hotspots and central pupil with single hotspot (maybe a little fuzz from the other reflections detectable around the outside with very bright LED torch but for all intense and purpose central view showed only P1.

The cheshire confirmed everything centered as well. Took me less than 15 minutes. Compared with 3 hours last night and 3 night before with no result.

I would suggest with the number of these fast imaging newts coming on the market that instructions for the catseye tools have a warning about the focal plane as it makes a HUGE difference.

The extension tube does add some error though, so now I need to look at getting a new autocollimator with extension built in.

Thanks for the help gents. One thing that does bother me a bit though is after all of this the glatter laser is not dead center of the hot spot. Even though Cheshire view is in middle and autcollimator shows what it should its about 1mm off center.


Edited by vman69au (08/28/12 08:04 AM)


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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: vman69au]
      #5390979 - 08/28/12 08:03 AM

Quote:

...I would suggest with the number of these fast imaging newts comming on the market that instructions for catseye tools have a waning about focal plane as it makes a HUGE difference....




There IS an "IMPORTANT" heads-up note about this at the top of the first page of the instructions here, but yes, a stronger message (and alternative product offering) to imagers with the built-in offset focal plane issue needs to be addressed. Stay tuned!

Edited by CatseyeMan (08/28/12 08:04 AM)


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vman69au
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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5390984 - 08/28/12 08:13 AM

Thanks Jim. So it is. This being my first newt I had no idea it wasnt on the imaging plane.

Edited by vman69au (08/28/12 08:18 PM)


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vman69au
journeyman


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Re: How to Collimate your Newtonian new [Re: vman69au]
      #5392539 - 08/29/12 01:17 AM

One other question. In the collimation video Jason made on YouTube from catsey eye website and the photos here, what were these taken with ? Seems like somehow a webcam or something was used to project collimation live.

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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: vman69au]
      #5392955 - 08/29/12 10:11 AM

Quote:

One other question. In the collimation video Jason made on YouTube from catsey eye website and the photos here, what were these taken with ? Seems like somehow a webcam or something was used to project collimation live.




Yes, I made a set of custom tools with a camera interface to facilitate production of the video. I had considered commercializing the system, but elected not to due to the prohibitive cost of the additional video support accessories needed (camera, battery pack, monitor, cables, case, etc ....) and the cumbersome (trip hazard) inherent with camera/monitor cabling (to the rear of the scope). I haven't given up though - I'm always exploring the new "wireless" technology for a practical & reasonably economical solution - stay tuned to CATSEYE ....


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Elric82
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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5397057 - 08/31/12 05:27 PM

Sorry if this has already been asked, but which is the better bet: catseye or a 2" howie laser? I'm gonna get both eventually, but can only get one now (bills are due). I'm leaning towards the laser cause it seems more simplistic. Anything has gotta be better than the stock z12 collimator (battery monster)!!!!

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Elric82
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5397059 - 08/31/12 05:32 PM

Ps:

Does the howie laser have a sight window like my stock collimator? Curious cause the picture I saw doesn't show one


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Vic Menard
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5397236 - 08/31/12 07:50 PM

If all you have is the stock windowed laser collimator to align your z12, and you intend to get a Glatter laser and CatsEye tools eventually, I would start with the TeleCat 2-inch combo tool. I would add the Glatter next (2/1.25-inch combo laser).

Later you could add the TuBlug window attachment...

If you decide to add coma correction, you may also want to consider an Infinity XLK autocollimator.


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sixela
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5397652 - 09/01/12 03:39 AM

Quote:

Does the howie laser have a sight window like my stock collimator?



No, it doesn't, because you're supposed to read the screen from the other end, through the telescope side of the focuser (either directly or through the reflections). If you really want to read things on the eyepiece side, you also need a TuBLUG.


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Elric82
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5397710 - 09/01/12 06:45 AM

So, I just looked on the catseyecollimation web page and was looking at the starterset XL. It comes with the hot spot , teletube XL, and blackcat XL cheshire. Is this alone sufficient for accurate collimation? It just doesn't look like much for $160

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Vic Menard
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5397886 - 09/01/12 10:47 AM

Quote:

So, I just looked on the catseyecollimation web page and was looking at the starterset XL. It comes with the hot spot , teletube XL, and blackcat XL cheshire. Is this alone sufficient for accurate collimation? It just doesn't look like much for $160



On the website the TeleCat XL is $116. For $15 more you can get a spot and a template. You could also use a simple notebook reinforcement ring although I prefer a perforated triangle when using my Glatter laser.

The TeleCat has a built-in Cheshire which should serve you well until you get your Glatter.

To answer your question, the TeleCat combo tool is sufficient for accurate collimation of a z12 w/o coma correction. If you decide to add a Paracorr later, the Glatter will provide the additional accuracy required for the focuser axial correction.


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Elric82
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5398230 - 09/01/12 02:24 PM

Mr.Venard:

Well Vic, I finally called Jim, thanks to you, and I believe I will be satisfied with the tools. Jim pretty much cleared everything up for me on how these tools work. Im assuming the booklet I'm getting as well is something you authored? Anyway, will hopefully be making the transaction within a few hours. Im getting the 2 piece combo set and booklet, plus hot spot and template. I'm sure hoping to be able to "master" these tools fairly quickly so as soon as the remnants of Issac clear out of here I can start viewing again. I'm sure this has to be better than the zhumell laser. Will I notice a difference between the effect on the views between these tools and the junky laser I now have? Thanx for youre responses and recommendations.


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Elric82
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5398379 - 09/01/12 04:33 PM

Sorry for the incorrect spelling of you're name

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Howie Glatter
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5398689 - 09/01/12 08:41 PM

Hi Elric, By clicking on edit in the title bar of your post, you can go back and correct spelling, and any other errors in posts. If you do this you can also change the contraction for "you are" (you're) to the posessive pronoun (I think), "your"
Please don't take my suggested corrections negatively; thinking of Clint Eastwood, "You made my day".


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Elric82
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Re: How to Collimate your Newtonian new [Re: Howie Glatter]
      #5399306 - 09/02/12 09:24 AM

No problem Howie. Thanks for the info. Will be talking soon again though, as I'm in the market for one of you're lasers. I never was much in english class though , always preferred math and science.

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GOLGO13
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5399379 - 09/02/12 10:33 AM

Here is my biggest issue with secondary positioning. I loosen the 3 screws and adjust the position to where it is circular. But when I go to tighten those screws again it all gets out of whack. Even to be able to access those 3 screws I have to hold the secondary holder in a weird position. Is there any tricks out there other than having my wife help? Would getting something like a bob's knobs help? Do those lose their collimation easier?

If it were not for this step overall collimation would be a lot easier.


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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: GOLGO13]
      #5399661 - 09/02/12 01:44 PM

Quote:

Here is my biggest issue with secondary positioning. I loosen the 3 screws and adjust the position to where it is circular. But when I go to tighten those screws again it all gets out of whack. Even to be able to access those 3 screws I have to hold the secondary holder in a weird position. Is there any tricks out there other than having my wife help? Would getting something like a bob's knobs help? Do those lose their collimation easier?

If it were not for this step overall collimation would be a lot easier.




The trick is to only turn the screws in incremental repetitive amounts each time (tightening one and loosening the other two) so that not too much compression force against the swivel point is lost to cause everything to unravel. Many folks find that replacing the original screws with longer bolts or knobs makes accessing them a lot easier. I actually replaced my phillips-head ones with hex-head bolts and I use a ball-point hex driver to access them.


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GOLGO13
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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5399832 - 09/02/12 03:50 PM

Thanks CatseyeMan. That worked pretty good and was a bit less painful. I've been thinking about getting one of your site tubes. I have an old Tectron set which is 1.25. I feel it works OK, but I may get a 2 inch site tube for my 10 inch just to be sure. However, I rarely use 2 inch eyepieces...partially because I only have one and it's a cheap 30mm GSO.

Thanks again!


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Starman1
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Re: How to Collimate your Newtonian new [Re: GOLGO13]
      #5399919 - 09/02/12 05:06 PM

Quote:

Thanks CatseyeMan. That worked pretty good and was a bit less painful. I've been thinking about getting one of your site tubes. I have an old Tectron set which is 1.25. I feel it works OK, but I may get a 2 inch site tube for my 10 inch just to be sure. However, I rarely use 2 inch eyepieces...partially because I only have one and it's a cheap 30mm GSO.

Thanks again!



The accuracy of your collimation depends on having accurate tools and achieving accurate registration for those tools in you focuser.
Every intermediate step of registration introduces another source of error into the possibility of accurate alignment.

Hence, the use of a 2" tool in a 2" focuser has the plus and minus tolerances of the registration between two pieces--the tool and the focuser.

When you add a second, intermediary, piece, you introduce an extra variable in registration: Tool>>Adapter>>Focuser, where >> represents a possibility of registration errors.

You can test adapters (or simply get a Glatter Parallizer) for accuracy until you get an accurate one, or, much more simply, use 2" tools in 2" focusers and eliminate a source of error.

And I was only referring to registration errors. There is also the possibility, with an adapter, of central hole alignment error, in which case perfect registration still results in alignment errors.

Better to eschew the use of adapters altogether if you have the choice. Errors in registration, when an eyepiece is used, are tolerable to the eye. Errors in registration during collimation result in visible errors in collimation.


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GOLGO13
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Re: How to Collimate your Newtonian new [Re: Starman1]
      #5400103 - 09/02/12 07:48 PM

I do have a 2 inch / 1.25 glatter laser (quite nice in my opinion). But my site tube is 1.25. So I'll probably pickup a 2 inch site tube at some point.

Do the Catseye cheshires work with the original donut hole center mark? Or do they need the triangle?


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Starman1
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Re: How to Collimate your Newtonian new [Re: GOLGO13]
      #5400163 - 09/02/12 08:44 PM

Quote:

I do have a 2 inch / 1.25 glatter laser (quite nice in my opinion). But my site tube is 1.25. So I'll probably pickup a 2 inch site tube at some point.

Do the Catseye cheshires work with the original donut hole center mark? Or do they need the triangle?



My last 12.5" f/5 scope had a 5/8" white reflective donut. In a cheshire, there was a small black annulus outside the donut (in between the white annulus of the cheshire and the smaller donut of the mirror) that made it very clear when the donut was centered--it was easy to detect when the black annulus was skinnier on one side than the other.


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Elric82
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Re: How to Collimate your Newtonian new [Re: Starman1]
      #5406441 - 09/06/12 12:09 PM

I've been reading in some of the archived posts where someone had loosened the center screw on there secondary mirror (z12) thinking this was how you adjust the tilt of the secondary itself. Now I know this is not so, but as i am awaiting my sight tube/Cheshire tools and Vics book, I was curious if this is how you adjust the secondary so that it is directly under the focuser? Can't wait to get my new tools and booklet for sure.


Thanks ahead of time


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okieav8rModerator
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5406495 - 09/06/12 12:44 PM

Quote:

I've been reading in some of the archived posts where someone had loosened the center screw on there secondary mirror (z12) thinking this was how you adjust the tilt of the secondary itself. Now I know this is not so, but as i am awaiting my sight tube/Cheshire tools and Vics book, I was curious if this is how you adjust the secondary so that it is directly under the focuser? Can't wait to get my new tools and booklet for sure.


Thanks ahead of time




Yes it is. The tools you've ordered will help you do a good job of centering the secondary under the focuser.


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GOLGO13
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5406712 - 09/06/12 02:53 PM

Elric,

You may want to leave your secondary alone unless you find it's not correct. If your getting a site tube it should show you if it's correct or not though.

But yes...the screw in the middle adjusts the secondary mirror places towards and away from the primary mirror. The three allen screws adjust the tilt of the secodary mirror.


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Elric82
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Re: How to Collimate your Newtonian new [Re: GOLGO13]
      #5407082 - 09/06/12 07:05 PM

Golgo13

Yea, I hope I don't have to mess with the secondary other than tilt, which is no problem. But, there's only so many clear nights !! I hate to mess with the GSO laser. I'm done with it. Its gonna be clear here tonight, but the batteries are prolly dead. That's why I ordered Mr. Flys tools. And Vics book. I thought I posted this a while ago, but I forgot to send I think ( I was at work). I wonder how long it takes to get the collimation tools? I'm getting ancy. I hope one day I can understand collimation like Vic and Jim. It doesn't seem to bad, as I wrather enjoy it.

Regards. Mike


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Starman1
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5407201 - 09/06/12 08:08 PM

Here is a link to use with your new tools:
http://www.cloudynights.com/item.php?item_id=2677


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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5407365 - 09/06/12 10:01 PM

Quote:

... I wonder how long it takes to get the collimation tools? I'm getting ancy....



They will ship tomorrow and you should get them in Monday's mail.

Quote:

...I hope one day I can understand collimation like Vic and Jim...



We've all been where you are now. I've got a pretty strong hunch that come this time next month, you'll feel a lot more comfortable with collimation.


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Elric82
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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5407767 - 09/07/12 06:13 AM

Thanks Jim, I hope you're right

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Blaise
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Re: How to Collimate your Newtonian new [Re: Elric82]
      #5415830 - 09/11/12 06:05 PM

Does anybody use blue loctite on the locking screws? I'm having problems with mine backing out after long trips in the car.

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Peter Trinidad
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5519898 - 11/14/12 06:18 PM

Hi Vic:

I am having the hardest time trying to collimate a 3 inch, f/6 old red tube Edmund telescope which is from around the 1980's (about 18 inches long). There are several of them under the reflector section on cloudy nights.
The mirror is not adjustable and is set in one position with screws. The only mirror you can adjust by moving it left or right or by bending the metal stalk which is the secondary mirror. At the present time I am using a small, plastic eyepiece with a pinhole in the middle of it but at best adjusting the secondary the stars look like "seagulls" and the moon looks out of focus at best. Someone told me that if you cannot adjust the primary mirror that it would be very difficult to collimate.

What are your thoughts?

Peter


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sixela
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Re: How to Collimate your Newtonian new [Re: Peter Trinidad]
      #5520931 - 11/15/12 10:31 AM

That is correct: if you can move only one mirror you can get rid of coma in the centre of the image or focal plane tilt but to eliminate both you need to be lucky...

I'd just determine where the focal plane is and use a Cheshire or collimation cap with its pupil close to that focal plane; centre the collimation cap pupil in the centre spot or make the centre spot concentric with the Cheshire ring. And live with the focal plane tilt...

If you don't have a centre spot either then it's even more difficult to do something sensible, really.


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Vic Menard
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Re: How to Collimate your Newtonian new [Re: sixela]
      #5520948 - 11/15/12 10:42 AM

Hi Peter,
Without a closer look at the mechanicals, I have to agree with Sixela's suggestions.

The only other possibility I could think of was to look at the way the primary mirror is mounted in the OTA (I couldn't find a good picture online). If it's cemented in place, your options are much more invasive. But if it's mounted in place with a few screws it may be possible to widen the screw holes enough to provide a small amount of tilt adjustment to the mirror/cell assembly. That's the way my refractor lens is mounted and it has plenty of tilt adjustment...

Edited by Vic Menard (11/15/12 10:43 AM)


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redsun
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Re: How to Collimate your Newtonian new [Re: Vic Menard]
      #5549252 - 12/01/12 06:58 PM

hey Vic i just replaced the 8" mirror on my orion reflector along with new spiders i have collamated it like i always do the when i insert a 25mm and try to focus an object 1/4 mile away it will not come in to focus. im not new to reflectors owend them since i was 18 now 55 lol i need held

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CatseyeMan
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Re: How to Collimate your Newtonian new [Re: redsun]
      #5549348 - 12/01/12 08:17 PM

Quote:

hey Vic i just replaced the 8" mirror on my orion reflector along with new spiders i have collamated it like i always do the when i insert a 25mm and try to focus an object 1/4 mile away it will not come in to focus. im not new to reflectors owend them since i was 18 now 55 lol i need held




Jumping in, I suspect your new mirror has a shorter or longer focal length than the original which has put your 25mm out of focus range. If the image gets sharper racking the focuser in, loosen all 3 Primary collimation screws about 5 turns, recollimate the Primary and try again to focus. If the image gets sharper racking the focuser out, tighten all 3 collimation screws about 5 turns, recollimate the primary and try again to focus.


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Jason D
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Re: How to Collimate your Newtonian new [Re: CatseyeMan]
      #5549369 - 12/01/12 08:34 PM

Tell us more about your mirror replacement. Did you take the focal length into account as Jim mentioned?

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hoa101
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #5571308 - 12/14/12 06:38 PM

I had a quick question about the "carefully decollimated" procedure that may be answered somewhere already... just cannot find it.

Anyway, after we've aligned the center spot with the sight tube, and the axial alignment with the procedure, won't the diagonal mirror always end up with the center spot no longer perfectly centered in the crosshairs of the sight tube? Anytime you adjust the tilt of the diagonal, it seems like it will end up a touch off. Or at least it does whenever I try to collimate in this manner on my dob.

Hopefully somebody can set me straight. Thanks.


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Starman1
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Re: How to Collimate your Newtonian new [Re: hoa101]
      #5571340 - 12/14/12 07:00 PM

The alignment of crosshairs with center spot on primary makes sure the focuser axis is aligned with the optical axis.
When you use the cheshire, next, to center the primary's center marker in the dark center of the bright annulus in the cheshire (i.e. if you have a combination tool you ignore the crosshairs for this part), you align the optical axis of the primary with the optical axis from the focuser.

The CDP procedure is used if you have an autocollimator, and the tiny tweaks necessary to correct the secondary won't really throw the crosshairs of the sight tube out enough to misalign the crosshairs and center marker.
You only decollimate the primary when doing this procedure so you can see the two images from the secondary and stack them perfectly. THEN you re-collimate the primary to stack all 4 images.

If you don't have an autocollimator, CDP has no meaning. Then it's simply:
--align secondary until crosshairs and primary mark line up.
--align primary until center mark is in center of dark area in cheshire.


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hoa101
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Re: How to Collimate your Newtonian new [Re: Starman1]
      #5571408 - 12/14/12 07:38 PM

I have the full catseye set actually, including the new two-holed auto-collimator. You're right that the adjustments from the procedure do not throw the crosshairs off much. Usually they still hit the center spot somewhat. Usually on the edge or something, not centered. I've heard the secondary alignment does not need to be very accurate, but what is accurate enough?

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Starman1
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Re: How to Collimate your Newtonian new [Re: hoa101]
      #5571477 - 12/14/12 08:19 PM

The tiny tweaks necessary to the secondary in the lateral pupil of the XLK are typically so small the resolution of the crosshairs wouldn't allow you to see the crosshairs drifting away from the center of the center marker.

So what you have are two tools that don't agree.

First, are you tightening the focuser's setscrew on the tools? If not, the different weights of the tools could result in different registrations. You don't need to really haul down on the setscrews, but they should be snugged against the tools so you can't move the tools in the focuser.

Second, have you made sure that when the teletube was expanded that it was not off angle? Measure the distance from the shoulder of the tool to the end of the tube in several places and make sure it's the same to your ability to read the length. If it isn't straight, loosen the tiny screws and adjust it until it is.

Third, check the accuracy of the XLK autocollimator. Loosen the setscrew, rotate it in the focuser 90 degrees and retighten. It should give the same reading all the way around. If it doesn't, it's possible it's not sitting flat in the focuser or that the mirror on the inside isn't dead on. If you suspect that, return the XLK to Jim to have him check it.

Fourth, I presume you are lining up the crosshairs near your eye (the ones hard to focus on) with the distant center mark? The distant, smaller, reflected image of the crosshairs won't line up until the primary is collimated.

Fifth, have you ever checked to make certain your primary mirror's center marker is centered? It could be off a bit.

Sixth, after aligning the secondary and primary and then inserting the AC, how far off is it? Are the 4 images of the center marker a jumble in the center, or are they way off? If they're way off, then you may not be reading the sight tube or cheshire accurately enough.
On my own scope, when I take care with the sight tube and cheshire, the 4 images are almost stacked.

Seventh, when you do the CDP procedure, how close to already stacked are the two images remaining in the center? I see mine nearly stacked and only a tiny tweak of the secondary is necessary to line them up.
You could ignore CDP entirely, tweak the secondary to line up the images in the XLK's lateral pupil, then realign the primary with the cheshire, followed by the secondary/lateral pupil of the XLK, followed by the cheshire, and repeated until neither tool shows any change is necessary (the tweaks get smaller and smaller with each iteration). The central pupil of the XLK will then show just one image of the center marker on a jet black background, and if you reinsert the sight tube, the crosshairs should line up perfectly on the center marker.


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Allan...
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Re: How to Collimate your Newtonian new [Re: Starman1]
      #5833579 - 05/01/13 02:06 AM

I know this question belongs in the beginners section but the thread was already started here, so here is my question (as odd as it might seem). Is it best to collimate (I use a laser) INside my residence before moving the scope (8" dob) outside, or wait til I'm outside; just in case I might bump it on the way out (its only a 50 ft trek and so far haven't hit anything). Im hoping the answer is INside as thats where I have been doing it so far. thanks, Allan

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beatlejuice
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Re: How to Collimate your Newtonian new [Re: Allan...]
      #5833596 - 05/01/13 02:31 AM

Unfortunately I am pretty sure that most of us collimate when the scope is at its final resting place for observing. But that doesn't mean that your 8 inch won't hold its inside collimation pretty well as you carefully take it outside. Its just better in the long run to check it again when you get there.

Eric


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Jason D
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Re: How to Collimate your Newtonian new [Re: Allan...]
      #5833608 - 05/01/13 02:56 AM

Quote:

so here is my question (as odd as it might seem). Is it best to collimate (I use a laser) INside my residence before moving the scope (8" dob) outside,



This is a common question in forums -- not as "odd" as you might think.
The answer is complete the initial collimation inside then take your scope outside and wait until it cools down before checking collimation one more time. It might need little collimation touch up.
I suggest pointing the OTA at 45 degrees angle when collimating.
Jason


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beatlejuice
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Re: How to Collimate your Newtonian new [Re: Jason D]
      #5834526 - 05/01/13 02:24 PM

Quote:

The answer is complete the initial collimation inside then take your scope outside and wait until it cools down before checking collimation one more time. It might need little collimation touch up.




I never thought about that Jason. Assuming the scope is not moved in the interim what happens in the 1-2 hours of cooldown to change the collimation?

Eric


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michaeldurban
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Re: How to Collimate your Newtonian new [Re: travvy]
      #6143265 - 10/17/13 04:18 PM

you lost me at mechanical focusser axis...

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Vic Menard
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Re: How to Collimate your Newtonian new [Re: michaeldurban]
      #6143316 - 10/17/13 04:55 PM

The "mechanical" focuser axis is what you set up mechanically (with rulers, squares, etc.) usually relative to the OTA (and sometimes relative to the mounting itself). The term is often described as "squaring" or "orthogonal" correction. The optical focuser axis is set up with a laser, sight tube, or autocollimator relative to the center of the primary mirror which is the origin of the primary mirror (or optical) axis.

Ideally, the two are the same (the mechanical and optical focuser axes). In practice, there is often some variance.


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