You are not logged in. [Login] Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar

Equipment Discussions >> Reflectors

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | (show all)
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Vic Menard]
#2795865 - 12/09/08 03:56 PM

Vic, I only included images 3+4*N where N is an integer.
I did not include the other images
0+4*N <== P
1+4*N <== 1
2+4*N <== 2
With a 2-way mirror, all N's are visible.
With a pupil, only N=0 is visible.

Note#1: Starting with N=1, the center spot will become an obstacle to reflections; however, when the AC is above the focal plane, the edges of the magnified images will not strike the center spot and will continue their reflection journey

Note#2: Interestingly, I am noticing the center of each consecutive larger image will minutely shift away from the primary center in the example I included in the previous post. I believe this is due to parabolic effect maybe!!

Jason

 Post Extras:
Vic Menard
Post Laureate

Reged: 07/21/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: Jason D]
#2795905 - 12/09/08 04:21 PM

I wonder if you could model P and 3 only and show how the stack varies as distance from the focal plane increases (and decreases). It might also be interesting to show the relative distance from the focal plane as a percentage of the focal length.

 Post Extras:
LcJ
sage

Reged: 01/18/08

Loc: Crowley, LA and Monroe, LA
Re: Catseye vs. Howie Glatter and Blug?? [Re: Starman1]
#2795962 - 12/09/08 04:45 PM

The more I think I know, I come to realize it is really only indicative of how little I truly do know. This also explains why sometimes the image is perfect and without noticably moving it changes. I could be an eyemovement, a contact lense shift, or drying or both or a myriad of other things. So for me collimation will have to be in a bell shaped curve with a certain level of confidence. Outside that level and it is out, inside that range it is in. But perfect collimation is probably a constant variable that is within the range of not being noticeable.

Probably it is like the perfect cherry blossom the last Samurai was looking for. Many are beautiful but so few are perfect.

Never the less, I am going to strive for as close as I can get, knowing full well I ain't there, but if it is close, I don't think my eyes will know the difference.

Thanks again,
Lyle

 Post Extras:
Vic Menard
Post Laureate

Reged: 07/21/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: LcJ]
#2796002 - 12/09/08 05:09 PM

Quote:

...explains why sometimes the image is perfect and without noticably moving it changes. I could be an eyemovement, a contact lense shift, or drying or both or a myriad of other things...

Lyle,
It's not that sensitive (at least, it shouldn't be!)
Like I mentioned in my earlier post, I can align my 22SST f/4 with the Glatter and 1mm aperture stop and I often find the autocollimator shows a perfect stack with no additional tweaking. My mechanicals are top notch (including a FeatherTouch focuser) but I would think once your primary and secondary mirror are secure your focuser should deliver similar registration consistency. Sometimes I pop the Infinty XL in the focuser and I see a close jumble until I gently tighten the retaining screw. Other times I can just apply a little pressure to the Infinity XL in the direction the retaining screw will move it and the reflections immediately stack on their own.

All the noise you're hearing about how critical the Infinity XL is, is only true if there are residual axial errors. Once the errors are corrected (and the Glatter 1mm aperture stop does a heckuva job correcting them, as does the CDP procedure), stacking the reflections in the Infinity XL is really pretty easy...

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Vic Menard]
#2796418 - 12/09/08 09:09 PM

Quote:

I wonder if you could model P and 3 only and show how the stack varies as distance from the focal plane increases (and decreases). It might also be interesting to show the relative distance from the focal plane as a percentage of the focal length.

Vic, based on ray simulation, the error can't exceed the distance between the pupil hole center and the optical axis.

When the pupil hole is at the focal plane, the error is zero. As the AC is raised, the error starts increasing gradually and approaches the distance between the center of the pupil hole and the optical axis.

Therefore, the error seems to be less than the CDP error introduced by the pupil hole size.

Jason

 Post Extras:
Vic Menard
Post Laureate

Reged: 07/21/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: Jason D]
#2796464 - 12/09/08 09:26 PM

Jason,
I apologize, I should have stated the scenario more clearly.
I'm not concerned about a CDP scenario--it makes sense that if the primary mirror is decollimated a certain amount at the focal plane, that amount will change as the pupil position is moved along the focuser axis.

What I would like to see modeled is the behavior of the stack when both axes are fully corrected. It makes sense that the magnification will be different for the reflections at different focal distances (i.e., P and 3 or P and 1) as the pupil is moved away from the focal plane. Similarly, the magnification factor may be able to be tied to the relative distance from the focal plane (as a percentage of the focal length). This would effectively model what Don is seeing in the coaxially aligned autocollimator as he racks the focuser in and out. And it may also be useful when one needs to determine the location of the focal plane...

I'm not sure if that's clearer or not?

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Vic Menard]
#2796784 - 12/10/08 12:13 AM

Vic, here is what I came up with

First column is the percentage of AC hieght above focal plane with respect to the focal length.
The remaining columns correspond to magnification% of "1", "2", and "3" with respect to "P".
"1" gets smaller, "2" and "3" get larger but "3" has faster rate.
Jason

0.0% |100% | 100% | 100%
2.0% | 96% | 104% | 109%
3.2% | 94% | 106% | 115%
4.0% | 92% | 108% | 120%
5.2% | 90% | 110% | 127%
6.4% | 87% | 112% | 136%

 Post Extras:
Nils Olof Carlin
Pooh-Bah

Reged: 07/26/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: Starman1]
#2796986 - 12/10/08 06:29 AM

Quote:

Now to come up with a simple method for determining the focal plane of the scope--waxpaper?

Any thin paper across the focuser opening, and the moon not obscured by clouds...

Nils Olof

 Post Extras:
auriga
Pooh-Bah

Reged: 03/02/06

Re: Catseye vs. Howie Glatter and Blug?? [Re: Starman1]
#2797416 - 12/10/08 12:19 PM

(snip)
Let's say you adjust the secondary to put the laser beam outside the primary's centermark. Could you adjust the tilt of the primary to return the beam to its source on the bottom of the laser? Yes. Would the telescope be collimated? No. The point is, there will be some error in having the laserbeam hit the center of the primary, but you can always adjust the primary to return the beam to its source. And, with most lasers, estimating the center of the primary's mark to the necessary degree of precision isn't possible because the eye is either too far away, the beam is too bright, or the beam shape isn't small enough to accurately assess the center of the mirror closely.

(snip)

Don,
Very lucid statement. You have a flair for writing.

(snip)
For now, though, we have a handful of companies producing good tools, and that is probably enough.

(snip)
Don,
Okay, I'll bite. Could you list some members of this handful? In addition to Howie Glatter, who else makes sufficiently reliable laser collimators, in your experience?

Thanks,
Bill Meyers

Edited by auriga (12/10/08 12:22 PM)

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: auriga]
#2797433 - 12/10/08 12:30 PM

Quote:

Could you adjust the tilt of the primary to return the beam to its source on the bottom of the laser? Yes. Would the telescope be collimated? No.

I just wanted to add that under the above scenario described by Don, the lateral error at the focal plane will be 1/2 the lateral error at the primary surface. That is, a laser beam that misses the primary center by 4mm will shift the primary focal point by 2mm away from the focuser axis.
Jason

 Post Extras:
Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Catseye vs. Howie Glatter and Blug?? [Re: auriga]
#2798717 - 12/11/08 02:09 AM

Quote:

(snip)
Let's say you adjust the secondary to put the laser beam outside the primary's centermark. Could you adjust the tilt of the primary to return the beam to its source on the bottom of the laser? Yes. Would the telescope be collimated? No. The point is, there will be some error in having the laserbeam hit the center of the primary, but you can always adjust the primary to return the beam to its source. And, with most lasers, estimating the center of the primary's mark to the necessary degree of precision isn't possible because the eye is either too far away, the beam is too bright, or the beam shape isn't small enough to accurately assess the center of the mirror closely.

(snip)

Don,
Very lucid statement. You have a flair for writing.

(snip)
For now, though, we have a handful of companies producing good tools, and that is probably enough.

(snip)
Don,
Okay, I'll bite. Could you list some members of this handful? In addition to Howie Glatter, who else makes sufficiently reliable laser collimators, in your experience?

Thanks,
Bill Meyers

Bill,
Though this is probably not a complete list, I have experience with the following brands of collimation tools and all seem excellently made and executed: Tectron, Catseye, Astrosystems, Howie Glatter, FarPoint. There are others, probably, but these I can vouch for, having tested the tools in jigs. I have tested other tools not as accurate--for instance one brand of combination cheshire/sight tube in which nearly all the crosshairs were off center (!).
And, to be fair, several brands of lasers can be collimated, even if they don't come out of the box that way.

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Starman1]

Vic, Jim, Nils Olof,

What do you think about the following idea?
Instead of placing the pupil hole dead center in the autocollimator, let us place it off-center. The amount of the offset equals the distance between the triangle spot center and the tip of the triangle.

Here are the highlights of this idea  at least according to my light ray analysis

1- All images will remain  none will disappear
2- Can be use to adjust both the focuser and primary axes alignment
3- Focuser axis alignment is met when triangle tips of images 1 and 4 touch. This is based on the exact same principle as Vics CDP. The only difference, images 1 and 4 will touch tips instead of forming the Star of David. Sensitivity is 2X against focuser axial errors and no sensitivity against primary axial errors  good for isolation (same as CDP)
4- Primary axis alignment is met when images 1 and 3 form the Star of David. Image 3 is brighter/crispier than image 4 which will make it easier to align. Furthermore, image 3 will not disappear upon perfect collimation. EVEN BETTER, sensitivity is 4X which will further perfect the critical primary axial alignment. According to my analysis, the 4X sensitivity is true for both focuser and primary axes  two birds with one stone.
5- The final perfect collimation image will display two Star of Davids with touching tips.
6- Note: The autocollimator will have to be rotated in the draw-tube to line-up all images  no more jumbled images.

Assuming I did not mess up in my analysis, this approach seems to be the right way to build auto-collimators.

Again, the main two highlights are:
1- No disappearance acts
2- 4X sensitivity

Few more Notes:
1- If the pupil offset can't be smaller than the radius of the center spot. If it is larger, then the Stars of David will still form but will not be touching. Not as nice but still manageable.
2- Another twist to the idea is to have another pupil -- same offset but at 90 degrees. That will give the user two ventage points to align the images.
3- The 90 degree pupil holes can have different offsets. Only one that is closer to the radius of the center spot (but not smaller) can be used and the other ignored.
4- We can't have two opposite pupils opposite otherwise the disappearance act will surface.
5- Maybe having 3 pupils at 120 degress is not a bad idea.

Jason

Edited by Jason D (12/12/08 03:57 AM)

 Post Extras:
Vic Menard
Post Laureate

Reged: 07/21/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: Jason D]
#2800836 - 12/12/08 07:29 AM

Quote:

...What do you think about the following idea?

I think it's dependent on establishing the primary mirror axis first before attempting to align the parallel axes--and verifying the primary mirror axis after would also seem prudent.

It's possible to align the axes parallel to each other with too many variables--distance between axes, direction (vector--think 3D), pupil position relative to focuser axis and focal plane. This would seem to require that at least one axis be verified redundantly...

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Vic Menard]

Quote:

I think it's dependent on establishing the primary mirror axis first before attempting to align the parallel axes--and verifying the primary mirror axis after would also seem prudent.

Vic, I would start off with aligning the focuser axis first then the primary. See attachment. Starting off with a slightly miscollimated setup, I would rotate the pupil-offsetted-AC to line up all images, then use CDP to align the focuser first by establishing a bow tie shape (images 1 & 4). Finally, I will align the primary with great precision by forming the two Stars of David (images 1 & 3). Image 4 location is insensitive to primary axis rotation around the primary center. That is, as long as the focuser axis alignment maintained, image 4 location will remain stationary.

Come think of it, for this proposed method, I would not use triangles -- plain circular donut spot might be better -- because there is no guarantee we will end up with the right triangle orientation as shown in the attachment.

Jason

 Post Extras:
Vic Menard
Post Laureate

Reged: 07/21/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: Jason D]
#2801122 - 12/12/08 11:08 AM

Quote:

...rotate the pupil-offsetted-AC to line up all images, then use CDP to align the focuser first by establishing a bow tie shape (images 1 & 4)...

Using round center spots instead of triangles, what would happen if 4 was aligned to the right of 1 instead of to the left? It seems to me the primary mirror axis would move to the left of the pupil? Wherever the pupil is placed, you can make the two axes parallel, and you can vary the distance between the axes as well...

I suppose you could verify the alignment by rotating the autocollimator. Properly aligned, the 2-4 hexagram should orbit the 1-3 hexagram--I think...

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Vic Menard]

Quote:

what would happen if 4 was aligned to the right of 1 instead of to the left? It seems to me the primary mirror axis would move to the left of the pupil?

Good point, Vic
I reran ray simulation and sure enough I can achieve two Stars of David when both focuser/primary axes are parallel using the off-axis-pupil-AC -- see attachment. The two stars of David can be achieved by either having the AC axis run through the primary center (desired) or by having the pupil axis run through the primary center (undesired). These are the only two cases I found.

Quote:

I suppose you could verify the alignment by rotating the autocollimator. Properly aligned, the 2-4 hexagram should orbit the 1-3 hexagram--I think...

Another good point . Rotation will be the key to tell us if the AC axis (same as the focuser axis) coincides with the primary axis (perfect collimation). It will tell us if we have met the (desired) or (undesired) axial alignment as mentioned in the previous paragrpah.
Only and only when the AC axis coincides with the primary axis, 1/3 images and 2/4 images will rotate around their respective centers. In addition, 2/4 images center will rotate/orbit around 1/3 images center. In other words, the two Stars of David form will persist. If AC/primary axes do not coincide then the two Stars of David will disintegrate fast. This makes sense because image 1 is special in the sense it does not undergo any AC reflections. Therefore, unless the AC axis runs through the center of image 1, any AC rotation will give an orbital motion to image 1.

I still see advantages for the circular donuts. True that AC can be rotated to align the tips 1 and 4 triangles but that assumes focuser axial alignment  it is a catch 22.

Vic, do you agree with the two fundamental additional benefits for above scheme (off-axis-pupil-AC)?
1- All images will persist upon perfect collimation  no more disappearance acts
2- Image 3 alignment against image 1 for Primary axial adjustment has 4X sensitivity

Bottom line: 2X accuracy for focuser axial alignment (CDP) and 4X accuracy for Primary axial alignment and no more disappearance acts.

Jason

EDIT: Updated the illustration to show how to tell if the desired or undesird "8" shape was reached. The desired will maintain the "8" shape as the AC is rotated. The undesired 8 shape will maintain the two circles (or two stars of David) but the distance between them with vary with rotation.

Edited by Jason D (12/12/08 04:04 PM)

 Post Extras:
Vic Menard
Post Laureate

Reged: 07/21/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: Jason D]
#2801560 - 12/12/08 03:50 PM

Quote:

...Vic, do you agree with the two fundamental additional benefits for above scheme (off-axis-pupil-AC)?
1- All images will persist upon perfect collimation  no more disappearance acts
2- Image 3 alignment against image 1 for Primary axial adjustment has 4X sensitivity...

I agree on both points. But I'm uncertain about the procedure for using the tool without first using an autocollimator with a centered pupil to reduce the axial errors sufficiently to make the off-axis pupil autocollimator primary mirror axis sensitivity useful (boy that's hard to read!).

It's one thing to utilize rotation (with the retaining screw tightened to reduce precession/epicycling) to verify the autocollimator--but using it as part of the collimation procedure...

Still--the concept certainly qualifies for the most interesting "out-of-the-box" autocollimation idea I've heard in quite some time!

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Vic Menard]
#2801613 - 12/12/08 04:16 PM

Quote:

I agree on both points. But I'm uncertain about the procedure for using the tool without first using an autocollimator with a centered pupil to reduce the axial errors sufficiently

Using the cheshire is still a recommended tool to use with today's AC. I suppose using a quality cheshire will bring it close to start making use of the off-axis-pupil AC.

Quote:

It's one thing to utilize rotation (with the retaining screw tightened to reduce precession/epicycling) to verify the autocollimator--but using it as part of the collimation procedure...

Rotation will be used to ensure the "desired" 8 shape was reached -- not the "undesired" 8 shape -- refer to my last updated post. Rotation can also be used to align the tips of images 1 & 4 tips once a relatively good focuser axial alignment is reached. However, for the final fine tuning adjustments, rotation will not be part of the fine tuning procedure.

Quote:

Still--the concept certainly qualifies for the most interesting "out-of-the-box" autocollimation idea I've heard in quite some time!

Jason

 Post Extras:
Jason D
Postmaster

Reged: 10/21/06

Loc: California
Re: Catseye vs. Howie Glatter and Blug?? [Re: Jason D]

Note: The following post was updated based on feedback from Vic.

Assuming we have an off-axis-pupil-AC with a pupil offset equals to the primary center spot radius. These are the steps for the proposed tool.

Step 1: PRE-WORK: Use any collimation tool(s) of your choice to bring collimation as close as possible to perfection.

Step 2: FOCUSER AXIAL ALIGNMENT: Insert the off-axis-pupil-AC into the draw-tube. Rack the drawtube to place the AC mirror surface as close as possible to the focal plane. You might see reflections similar to figures A or D. Rotate the off-axis-pupil-AC to line up the triangle tips of images 1 and 4. In case the tips are separated (figure B) or overlapped (figure B), fine adjust only the secondary mirror until the tips of triangles 1 and 2 touch. If your starting point is figure D, then either ignore images 2 and 3 or minutely adjust the primary to get images 2 and 3 out of the way then proceed touch the tips of triangles 1 and 4 as described above. Now focuser axial alignment is met with 2X accuracy. This step is based on Vics CDP method.

Step 3: PRIMARY AXIAL ALIGNMENT: Adjust only the primary to bring images 2 and 3 into the view as shown in figure. In the process, image 2 might orbit image 1 which remains stationary. Note image 3. Proceed to form two hexagons as shown in figure E. Again, ignore any rotation or orbiting motions. Aligning images 1 and 3 will be more sensitive than images 2 and 4 because image 3 is 2X more sensitive than image 2. Now primary axial alignment is met

Step 4: ELIMINATING RESIDUAL AXIAL ERRORS: Rotate the off-axis-pupil-AC to line up images 1 and 4 triangle tips again then fine tune the secondary to touch both triangle tips. This fixes any focuser axial residual error. Then proceed to re-form the two hexagons by fine tuning the primary. This fixes any primary residual axial error.

Jim, if you ever consider building a prototype, I will be more than happy to evaluate it for you . 4X primary axial alignment accuracy, eliminating disappearance act, and eliminating the final CDP step (restoring primary axial alignment) might sound appealing

Jason

Edited by Jason D (12/13/08 09:49 PM)

 Post Extras:
Vic Menard
Post Laureate

Reged: 07/21/04

Re: Catseye vs. Howie Glatter and Blug?? [Re: Jason D]
#2802929 - 12/13/08 12:57 PM

Jason,
I don't know where to start...
There's one true axial reference--reflection 1. The autocollimator pupil itself has a known displacement from the focuser axis equal to the radius of the primary mirror center spot...

Since we know that the pupil is offset the radius of the center spot, it needs to be moved to the edge of 1. We know that when alignment is fully corrected, the foreground pupil will fall precisely between the two hexagrams. The background pupil is rotated 180-degrees relative to the optical axis, so it should appear on the opposite side of the 1-3 stack.

Given those conditions, the pupils should define the primary mirror axis, and rotating the autocollimator should cause the 2-4 stack (and both pupil reflections) to orbit the centered 1-3 stack.

What do you think?

Edited by Vic Menard (12/13/08 04:07 PM)

 Post Extras:
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | (show all)

Extra information
4 registered and 12 anonymous users are browsing this forum.

Forum Permissions
You cannot start new topics