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Catseye vs. Howie Glatter and Blug??

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#51 JR1560

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Posted 24 November 2008 - 02:48 PM

I believe too much is going into this discussion which is going nowhere. IMO, the Howie Glatter Laser with the Blug is the best value for the money, the simplest and one of the most accurate to use.

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#52 Vic Menard

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Posted 24 November 2008 - 02:56 PM

More likely, by "stacking" I think Don means tightening the jumble. If you do this by adjusting the secondary mirror, the primary mirror axis will be affected.

To me this means you never really got it stacked, just close. Or else it means that there's some AC tool-reading limitation where they look stacked but really are not.

I'm not sure what you mean. The scenarios I described can be verified by rotating the autocollimator in the focuser. With the iterative method, the two axial errors are systematically reduced until both tools (autocollimator and Cheshire) indicate proper alignment. With a zeroed primary mirror error courtesy of the Cheshire, the autocollimator shows focuser axial error (flanking reflections are offset 2X and 4X the focuser axial error). Attempting to correct the focuser axial error at the secondary mirror reduces the focuser axial error and imparts a small primary mirror axial error. Repeating the sequence ultimately reduces both errors to the readability of the tools.

Like I said in my previous post, decollimate the primary mirror to separate the reflections, zero the focuser axial error, and then zero the primary axial error. It's much quicker than the iterative method. :ubetcha:

#53 Vic Menard

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Posted 24 November 2008 - 03:00 PM

I just ordered Vic's new book: http://www.catseyeco...rspectives.html

I hope you enjoy the new book! If you have any questions, I'll be listening.

#54 hudson_yak

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Posted 24 November 2008 - 03:07 PM

This brings me back to my original question. How can AC images be perfectly stacked yet the cheshire indicate an error? At the same time? (As a hint, I don't believe it is possible, other than for tool registration or manufacturing accuracy differences.)

I'm not asking about the iterative process here. I'm asking about what two different tools indicate when all else is the same.

Mike

#55 Vic Menard

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Posted 24 November 2008 - 03:12 PM

...I believe too much is going into this discussion which is going nowhere. IMO, the Howie Glatter Laser with the Blug is the best value for the money, the simplest and one of the most accurate to use.

How is this discussion going nowhere? Each tool being discussed has particular strengths and weaknesses. When they're used in a complementary manner, the effect is synergistic.

Then again, I respected Don's passion for passive alignment tools, and I respect yours for Howie's laser solutions too! :bow:

#56 Vic Menard

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Posted 24 November 2008 - 03:26 PM

This brings me back to my original question. How can AC images be perfectly stacked yet the cheshire indicate an error? At the same time? (As a hint, I don't believe it is possible, other than for tool registration or manufacturing accuracy differences.)

No--it's quite possible. As I posted above, when the focuser axis and the primary mirror axis intersect at the radius of curvature, the two "upright" reflections stack on top of one another, and effectively stop the propagation of the inverted reflections, causing them to disappear from view (even though they may be widely separated on the other side of the autocollimator pupil)! With a triangular primary mirror center spot, the jumble looks like a bow tie or a diamond pattern (unless the paired triangles overlap a bit, as they would in a close jumble). So it's possible to accidentally stack the wrong two reflections in a close jumble and end up with what looks like a perfect stack, until you notice that the autocollimator pupil isn't centered in the center spot perforation. The autocollimator pupil/center spot perforation has the same sensitivity to primary mirror axial error as the Cheshire, 2X--but the pupil can be difficult to see depending on the lighting, the size of the center spot perforation, and how clean the stack is (no fuzziness around the edges). That's why you always verify the final alignment with the Cheshire (unless you can clearly see the pupil in the autocollimator).

#57 hudson_yak

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Posted 24 November 2008 - 03:38 PM

I mean all the AC images, which is what I read Don's post be to be talking about. In other words, the scope adjusted to what the AC is showing as fully-collimated, both secondary and primary.

He then went on to say the primary may still require tweaking. I don't understand it, unless the AC is unable to be read as accurately as the cheshire, which also seems to be what you are saying at the end of your paragraph here.

Mike

#58 Vic Menard

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Posted 24 November 2008 - 04:06 PM

I mean all the AC images, which is what I read Don's post be to be talking about. In other words, the scope adjusted to what the AC is showing as fully-collimated, both secondary and primary.

Well, obviously, if the reflections (images) are widely separated as in the bow tie or diamond presentations (figures 25 and 26 in the fifth edition), when the two inverted reflections suddenly disappear in the autocollimator mirror, you'll probably suspect something isn't right. Of course this requires both axes to have residual errors (the focuser axial error will be twice the linear offset of the primary mirror axial error). But when the reflections are nearly overlapped and the upright reflections are accidentally stacked, depending on the residual primary mirror axial error and the visibility of the pupil, it can look like a perfect stack.

He then went on to say the primary may still require tweaking. I don't understand it, unless the AC is unable to be read as accurately as the cheshire, which also seems to be what you are saying at the end of your paragraph here.

Well, the Cheshire only shows the primary mirror axial error (magnified 2X), where the autocollimator shows both axial errors. In a close jumble with two focused reflections and two unfocused reflections, it can be difficult to sort out what the reflections are indicating. The best solution, is to carefully decollimate the primary mirror and use the reflections to correct the focuser axial error first, then the primary mirror correction is easy and it has almost no affect on the corrected focuser axis. With the focuser axial error corrected, the flanking reflections in the autocollimator each show the primary mirror error magnified 4X relative to the primary mirror center spot (or a total of 8X if you measure from one flanking reflection to the other).

#59 mmagrunmo

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Posted 24 November 2008 - 04:35 PM

I mean all the AC images, which is what I read Don's post be to be talking about. In other words, the scope adjusted to what the AC is showing as fully-collimated, both secondary and primary.

He then went on to say the primary may still require tweaking. I don't understand it, unless the AC is unable to be read as accurately as the cheshire, which also seems to be what you are saying at the end of your paragraph here.

Mike


I do not have the experience of Don or Vic, but I use all of the tools being discussed here and think I may understand your confusion.

While the tools are indeed used individually, think of them as tools used together in an iterative way. The tools will indicate what they indicate, and if the ac shows that things are aligned, but a cheshire shows misalignment, you are not there yet. Eventually, if you keep at it, the tools will agree.

There are of course debates about whether or not you can see the difference at the eyepiece between pretty close and perfect with these tools, but it is possible to make them agree, and in my experience, it is well worth the effort.

#60 JR1560

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Posted 24 November 2008 - 04:47 PM

How is this discussion going nowhere? Each tool being discussed has particular strengths and weaknesses. When they're used in a complementary manner, the effect is synergistic.


I don't know anything about collimation. I'm trying to learn all that I can, so I can enjoy the Meade LB 16. In going thru all the products and writings, I find your writings and Catseye very confusing and complicated. [I haven't read your book]. The simplest and easiest I've come accross so far, is Howie Glatter. Actually HoTech is even simpler. But, I have been told the HoTech Laser isn't collimated. Perhaps that is where auto-collomation may come into play.

You guys are making this thread even more complicated. I say its going nowhere, IMO, based on Howie's information to me of "empty sensitivity, because the difference will not be visible in the eypiece"

Do you really need auto-collomation? Are you guys infering there can be no HD views without auto-collomation, in using the Howie Glatter Laser and Blug?

#61 Jason D

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Posted 24 November 2008 - 05:09 PM

You guys are making this thread even more complicated. I say its going nowhere, IMO, based on Howie's information to me of "empty sensitivity, because the difference will not be visible in the eypiece"


Those who only desire to learn how to drive cars should not read literature about how engines and transmissions work – it will be overwhelming and confusing.
Some have the desire to learn more about engines and transmissions to keep their cars fine tuned for optimal driving experience.

Same idea here: Some would only like to memorize simple collimation steps whereas others would like to understanding the math and theories behind these steps. It is a personal preference. Those who get deeper into the theory of collimation have the advantage of better assessing/optimizing their collimation with less effort.

Jason

#62 hudson_yak

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Posted 24 November 2008 - 05:51 PM

if the ac shows that things are aligned, but a cheshire shows misalignment, you are not there yet. Eventually, if you keep at it, the tools will agree.


Which, means, basically, that you got the AC to agree with the cheshire, the latter of which is the final arbiter between the two, despite the former's claims of expanding the sensitivity and visibility of collimation errors.

And in so doing, what you've really done is refine the focuser-end axis to a degree that is usually unnecessary, as the margin for error with that is pretty large. 1/30 of the primary diameter if not using a paracorr. It's quite likely thrown out a bit as soon as you take your 2" AC out and put in a 1.25 adapter and eyepiece anyway.

Mike

#63 hudson_yak

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Posted 24 November 2008 - 06:05 PM

But when the reflections are nearly overlapped and the upright reflections are accidentally stacked, depending on the residual primary mirror axial error and the visibility of the pupil, it can look like a perfect stack.


Interesting comment.

I suppose Don would have to chime in as to what he meant regarding the original point I raised.

Mike

#64 Vic Menard

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Posted 24 November 2008 - 06:07 PM

I don't know anything about collimation. I'm trying to learn all that I can, so I can enjoy the Meade LB 16.

That's a good start.

In going thru all the products and writings, I find your writings and Catseye very confusing and complicated.

I'm sorry, but then, in my defense (and Jim's), we're usually called upon when the alignment problem is not so simple.

The simplest and easiest I've come accross so far, is Howie Glatter.

If you've read my posts in this thread, you should know that I'm a bit of a Howie Glatter fan myself. The reason the Glatter laser is simple to use is because it is so precisely made.

Actually HoTech is even simpler.

How did you come to that conclusion?

But, I have been told the HoTech Laser isn't collimated. Perhaps that is where auto-collomation may come into play.

If you mean using another tool to verify the HoTech laser results, it would necessarily have to be a SCA tool also, or there will be discrepancies.

You guys are making this thread even more complicated. I say its going nowhere, IMO, based on Howie's information to me of "empty sensitivity, because the difference will not be visible in the eypiece"

Setting aside the precision of the tools, the OP asked for guidance re:Catseye (trio) vs. Howie Glatter and Blug for a 16inch LightBridge with a 2-inch focuser. Where the Glatter is an excellent choice for the focuser axis (1mm aperture stop) and the primary mirror axis (Barlowed laser accessories and 1mm aperture stop), the Catseye sight tube offerings are very good for secondary mirror alignment and the autocollimator is an excellent tool to verify that both axes are indeed coaxial and your alignment technique is good.

Do you really need auto-collomation?

No. I think I've been fairly clear on that point. But I do think you need a sight tube or similar tool for assessing secondary mirror alignment (which can get really messed up with laser-only alignment procedures) and I do recommend at least one redundant tool (preferably passive) to verify that the laser is still performing to spec.

Are you guys infering there can be no HD views without auto-collomation, in using the Howie Glatter Laser and Blug?

Not me. I'm not a big fan of the Blug (the 1mm aperture stop is my favorite Glatter accessory), but I've already said (more than once in this thread) that the Glatter with 1mm aperture stop is my "go to" tool after dark.

But we're not just talking about simple axial touch-ups--the OP requested recommendations for his LB, and he's received them. He too found the Catseye tools "complicated". I would note that the complication arises when secondary mirror alignment is considered. The good news is that a slightly misaligned secondary mirror has minimal impact on image performance. Truly, if you're not using a Paracorr, the focuser axial alignment is much more forgiving than the primary mirror axial alignment. This means you can have a pretty messed up collimation and a simple collimation cap may get you close enough for some on axis (center of the fov) performance. But generally speaking, primary mirror axial alignment is rarely the reason for a collimation thread.

I've posted this before, I'll post it again. In order of importance:

1.) Primary mirror axial alignment. Available collimation tools include the collimation cap, the Cheshire eyepiece, "combo" (Cheshire/sight tube) tools, autocollimators, the Barlowed laser, the Blug, and the tuBlug. Every one of these tools magnify the primary mirror axial error 2X (depending on the read, the autocollimator magnifies the error 2X, 4X, or 8X), and with the exception of the "combo" tool and the autocollimator, none are useful for focuser axial error correction.

2.) Focuser axial alignment. Available collimation tools include the sight tube, "combo" (Cheshire/sight tube) tools, autocollimators, and simple thin beam lasers. With the exception of the autocollimator, all tools magnify the focuser axial error 1X. Depending on the read, the autocollimator magnifies the error 2X, 4X or 6X.

3.) Secondary mirror alignment. Available collimation tools include the sight tube, "combo" (Cheshire/sight tube) tools, and holographic lasers. Personal preferences vary, but after years of use, I find the direct view in a sight tube easier to interpret than a holograph. However, after dark I use a holograph to verify the secondary mirror alignment.

Is it complicated? No more than it has to be. But if you don't understand, or don't want to understand, you can limit your alignment to primary mirror axis only, to primary and focuser axis only, or perhaps, to all three.

Regarding "empty" precision--I think that, too, has already been discussed. Again, please accept my apologies if my reasoning was too obtuse.

#65 DeepSpaceTour

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Posted 24 November 2008 - 06:18 PM

I believe too much is going into this discussion which is going nowhere.


... :question:...wow!! now this is a bizarre statement :foreheadslap:

This has been an excellent discussion on collimation practice and theory,using the different collimation tools and methods,explained by people, with real world experience,that has been very informative IMO,and probably others.You can't get enough info on this subject,as far as I'm concerned(this fact is born out in all the threads on the subject, and people asking questions) particularly to people just starting out and learning to collimate, the more clear, and concise, info out there, the better,obviously.

Clear skies.

#66 JR1560

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Posted 24 November 2008 - 06:46 PM

particularly to people just starting out and learning to collimate, the more clear, and concise, info out there, the better,obviously.


I disagree. Much of the info being put forth isn't clear and concise. It's overly complicated, technical, and theoretical. It departs from the simple question of Howie Glatter vs. Catseye. Which system is better?

So far I don't see any advantages of going any further than using Howies system of collomation. I'd rather spend my time "gazing upon the Heavens", rather than become obsessed with theoretical and unproven collomation techniques. "bizarre" I don't think so. I believe I'm right.

#67 gaz-in

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Posted 24 November 2008 - 06:48 PM

I too have found this discussion fascinating and informative....thanks to all that contributed!

#68 johnmc52

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Posted 24 November 2008 - 07:04 PM

Excellent advise Jason D. I agree with your statement 100%.

#69 GardnerPacificCA

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Posted 24 November 2008 - 07:10 PM

I just ordered Vic's new book: http://www.catseyeco...rspectives.html

I hope you enjoy the new book! If you have any questions, I'll be listening.


Many thanks for all your answers here Vic...I appreciate the discussion and hope to understand this thread more once I dive into your book when it arrives in a few days. My plan is to get an inexpensive dob while deciding on and waiting for a premium dob. Understanding collimation tools and technique will go a long way to ensure good results.
I would like to also thank all the contributors here...a great discussion and lots of interesting replies.

#70 Starman1

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Posted 24 November 2008 - 07:53 PM

I just ordered Vic's new book: http://www.catseyeco...rspectives.html

I hope you enjoy the new book! If you have any questions, I'll be listening.

Vic,
I found a few things needing updating in the book. I'll pass them along to you when I get the chance. Work is very heavy these days (about 14 hrs/day), but I'll try to get you the notes in the next few days.
I think the book is deviating a little from a HowTo to a Theory discussion. It might be a good idea for the 6th edition (! :lol:) to have a couple chapters on How To and then further chapters going into depth.
And, even though you've added a lot of pictures, it needs more.
I did learn a few things, though. Always do when you write about collimation.
Don

#71 Vic Menard

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Posted 24 November 2008 - 08:16 PM

Vic,
I found a few things needing updating in the book. I'll pass them along to you when I get the chance...I think the book is deviating a little from a HowTo to a Theory discussion.

It's hard to try to cover all aspects of a single element of collimation without delving into the conceptual semantics. I just dropped the simplified 2-page HowTo into Chapter 12.

It might be a good idea for the 6th edition (! :lol:)...

:bugeyes:

...even though you've added a lot of pictures, it needs more.

I already have Jim working on three more 3D graphic simulation series and one animation to go in the online addendum!

I did learn a few things, though. Always do when you write about collimation.


I kept adding and tweaking various pages/chapters right up until the book went to the print shop. Even with all of the proofreading and edits, I still missed a couple of errors (they were pretty minor) that I'll be addressing on the online addendum. But if you got some additional insight from the book, I can't have done too bad of a job!

#72 Starman1

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Posted 24 November 2008 - 08:57 PM

But when the reflections are nearly overlapped and the upright reflections are accidentally stacked, depending on the residual primary mirror axial error and the visibility of the pupil, it can look like a perfect stack.


Interesting comment.

I suppose Don would have to chime in as to what he meant regarding the original point I raised.

Mike

Mike,
If you collimate using first a sight tube, then a cheshire, then an autocollimator, I find the four centermarks stacked perfectly with the pupil of the AC slightly off-center in the stacked images. Returning to the cheshire shows the mark is now off center slightly. I suppose what has happened is that correcting errors in the secondary tilt has resulted in a change of the optical axis to the point where the formerly collimated primary is now off slightly. Recentering the mark in the cheshire and returning to the AC now shows the 4 images unstacked. Restacking them (I don't always need to decollimate the primary because I know which two are from the secondary and which from the primary) typically shows the dark center pupil of the AC is now closer to center in the stack. However, returning to the cheshire sometimes shows a slight error remains, even though the AC shows a good stack. But, when the AC shows a stack, the cheshire shows perfection, and the pupil of the AC shows exactly in the middle of the stack, and the AC field is black with no stray light, I call it quits.
This may seem complicated, but the whole process just took me longer to write than to do. I only ever spend more than 5 minutes at it if I'm being particularly fussy about the stack.

Now if I do use the carefully decollimated primary procedure and take my time to stack the secondary images first, I usually find that stacking the two primary-derived images on top of the secondary stack requires the adjustment of at least two primary collimation knobs. After that (Vic wouldn't be surprised), the cheshire shows perfect alignment at the same time as the AC.

I think that if you are careful with the sight tube, and the primary is not far out (from the last time you collimated), you can skip the cheshire and go directly to the autocollimator. And if the pupil in the center of the AC image is dead center, I don't even need to check the cheshire.

I'm not perfectly clear why I can get a good stack of the centermark images with the dark center pupil slightly off center in the stack. I leave it to Vic or Jason to explain that. I do know, however, that if the dark pupil in the center of the AC image is dead center in the stack that I will find no error in the cheshire.

I find this stuff fun. I will often push myself to make the alignment even more perfect, going so far as to miscollimate the scope to start from scratch to see if I can achieve an even better collimation. Perhaps all of this does not make any improvement in the star images, but there is satisfaction in knowing that if there is anything wrong with the star images that night at least one cause is removed.

#73 gaz-in

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Posted 24 November 2008 - 08:58 PM

Over the years, I have very much enjoyed brewing beer (and drinking it..but that is another thread). Brewing beer can be a simple enjoyable hobby or a complex enjoyable hobby....hence one of my favorite bumper stickers "Brewing Beer is Not Rocket Science...Unless you want it to be!" this thread reminds me of that...perhaps we need to have a varient of this saying....."Collimation is not rocket science...unless you want it to be!"

#74 panhard

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Posted 24 November 2008 - 09:08 PM

Wow what a great thread. :bow: :bow: :bow:

#75 auriga

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Posted 24 November 2008 - 09:36 PM

(snip)
Regarding "empty" precision--I think that, too, has already been discussed. Again, please accept my apologies if my reasoning was too obtuse. [/quote]

Probably not obtuse. Abstruse, maybe.
Bill Meyers


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