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Catseye vs. Howie Glatter and Blug??

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#226 Nils Olof Carlin

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Posted 07 December 2008 - 10:29 AM

Any 2-dimensional ray tracing scenario must be consistent with the progression shown here.


Or perhaps it is at least as fair to say that the simulation should be consistent with a 2-dimensional ray-tracking analysis? :lol:
It seems to be, here. As for the brightening after the 15th turn, this is about when the AC pupil will be imaged back, magnified to infinity, to fill the whole reflection. I don't know what the simulation assumes about what's behind the AC pupil, but in practical use the AC pupil will mostly reflect the dark interior of the eye (if smaller than the eye pupil - else with a thin rim of the iris, perhaps?).

Simulations are useful, but I like the real photos and videos on Vic's page - they are just a bit truer to life, showing the different defocus on the virtual images (2 and 4 of 4, or reflections 1 and 3 of 3 if you prefer) and real images.

Nils Olof

#227 Jason D

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Posted 07 December 2008 - 10:43 AM

Imagine this scenario - you have the bowtie pattern with the true and rotated pairs separated, but very little separation within each. Then you tweak the primary a little - enough to make the first pair stack and the second pair vanish. You might then -falsely- believe that you have true collimation.

Not too likely in practice, perhaps, but if you are not aware of this trap, you just may fall into it.

Nils Olof


Hi Nils Olof,
Do you agree with the following post about the BOW TIE scenario?
http://www.cloudynig...sb/5/o/all/vc/1
Jason

#228 CatseyeMan

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Posted 07 December 2008 - 10:55 AM

Any 2-dimensional ray tracing scenario must be consistent with the progression shown here.


Or perhaps it is at least as fair to say that the simulation should be consistent with a 2-dimensional ray-tracking analysis? :lol:


The PovRay software IS based exclusively on Ray Tracing algorithms. See: PovRay Functionality

Based on the incredible mathematical rendering of photographic realism generated by the real experts with this software, PovRay Render Examples, I have no doubt of its reflection progression accuracy.

Simulations are useful, but I like the real photos and videos on Vic's page - they are just a bit truer to life, showing the different defocus on the virtual images (2 and 4 of 4, or reflections 1 and 3 of 3 if you prefer) and real images.


Personally, I see no reason to show preference of one over the other - they serve 2 independent purposes. Photogrphaphs represents what the eye sees; accurate simulations like the PovRay virtual telescope are consistent with the photographs (except for the focal blur which actually can be simulated in PovRay with sufficient additional programming) help explain the real world reflective phenomenon of the A/C.

#229 CatseyeMan

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Posted 07 December 2008 - 11:00 AM

... I don't know what the simulation assumes about what's behind the AC pupil, but in practical use the AC pupil will mostly reflect the dark interior of the eye (if smaller than the eye pupil - else with a thin rim of the iris, perhaps?)


The simulation sequence has a a software optional "dark gray" mask placed in front of the AC pupil to simulate the effect of the eye interior.

#230 auriga

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Posted 07 December 2008 - 02:07 PM

Howie,
This thread is surely a tour de force.

As the thread indicates, an autocollimator provides a clarity and simplicity that will appeal to novices, particularly those with engineering or physics backgrounds.

But I am sticking wtih your laser collimator and tublug.

Bill Meyers

#231 Vic Menard

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Posted 07 December 2008 - 02:23 PM

Simulations are useful, but I like the real photos and videos on Vic's page - they are just a bit truer to life, showing the different defocus on the virtual images (2 and 4 of 4, or reflections 1 and 3 of 3 if you prefer) and real images.

Personally, I see no reason to show preference of one over the other - they serve 2 independent purposes. Photogrphaphs represents what the eye sees; accurate simulations like the PovRay virtual telescope are consistent with the photographs (except for the focal blur which actually can be simulated in PovRay with sufficient additional programming) help explain the real world reflective phenomenon of the A/C.

Interestingly, I find the visual appearance of the autocollimator reflections to be somewhere in between the camera and simulator appearances. The camera defocuses the minus one focal length reflections too much, and the simulator shows fine detail too easily. In use, particularly with daylight illuminated reflective white triangles, it can sometimes be difficult to judge which triangle is brighter than the next. Using a carefully decollimated primary mirror with a good autocollimator quickly sorts out the axial errors and easily delivers coaxial alignment.

#232 Don W

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Posted 07 December 2008 - 02:24 PM

I have added this thread to the "Best of Reflectors" thread stickied to the top of this forum.

#233 Vic Menard

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Posted 07 December 2008 - 02:45 PM

...As the thread indicates, an autocollimator provides a clarity and simplicity that will appeal to novices, particularly those with engineering or physics backgrounds.

Using the same logic, understanding how a laser works may also appeal to "those novices with engineering or physics backgrounds". Of course, you don't need to know how a laser collimator works to use one. Similarly, you don't need to know how an autocollimator works to use one with the CDP procedure--which does, in fact, clearly show both axial alignments and simplifies their reduction.

Unfortunately, you're unlikely to find an Infinity XL or a Glatter laser in the hands of a novice. They'll more likely be drawn to the one-step simplicity of an inexpensive windowed laser or perhaps an improper alignment procedure that leaves the focuser axis and/or the secondary mirror alignment for CN contributors to resolve in another lengthy offset and/or skew discussion.

Axial alignment is easy--whether your tool of choice is a Glatter laser or a Catseye autocollimator.

#234 Jason D

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Posted 07 December 2008 - 02:54 PM

Mike, how about the following simplified modeling of the 4 images (see attachment):

STEP 1: Select one of the 3 figures on the top based on AC tilt. To be more accurate, the AC mirror does not tilt in the focuser but rather tilting the secondary mirror will give the equivalence of a tilted AC mirror in this model. The secondary mirror was kept out of the model to simplify the model

STEP 2: Place a pupil point anywhere along the AC mirror. Draw a line from image "2" through the selected pupil hole, proceed an equal distance on the opposite side, and then flip the orientation of image "2". This models the refection of image "2" through the flat AC mirror. Do the same for image "4". There is one caveat: If you select the pupil hole where the AC axis runs through the ROC then images "3" and "4" will disappear.

Jason

Attached Thumbnails

  • 2792102-simplified_AC_image_modeling.JPG


#235 LcJ

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Posted 07 December 2008 - 05:21 PM

Please save me a lot of time reading and thinking. If when everything is apparently aligned and the Glatter and Blug indicate collimation and yet the AC pupil isn't centered, what is the most likely problem? I don't think mine has ever been aligned.

Thanks for the help.

#236 Jason D

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Posted 07 December 2008 - 05:38 PM

Lyle,
Refer to the following earlier post
http://www.cloudynig...sb/5/o/all/vc/1
If what you have is similar to Jim's pic then you might have run into the "bow tie" scenario. Refer to Vic's collimation page for more info about "bow tie"
http://homepage.mac....s/NPaddend.html
Another potential source could be a mis-centered triangle.
Jason

#237 Vic Menard

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Posted 07 December 2008 - 05:59 PM

Please save me a lot of time reading and thinking. If when everything is apparently aligned and the Glatter and Blug indicate collimation and yet the AC pupil isn't centered, what is the most likely problem? I don't think mine has ever been aligned.

If the AC pupil isn't centered in the front most center spot perforation, the primary mirror alignment is off. You should see the same alignment error using a Cheshire eyepiece, as the two alignments are identical.

The big question is why the error isn't visible using the Blug, which also works just like a Cheshire eyepiece (or collimation cap). To find out, try rotating both tools. If the pupil moves when you test the AC, you've found the problem. If the Barlow/emitter moves when you rotate the Blug, that's the problem. If you're using a 2- to 1.25-inch adapter with one tool and the other is a 2-inch tool, that could be the problem. Or you may find you have more than one problem that's keeping the two tools from showing good alignment simultaneously.

At f/4.7, the XT10 primary mirror axial tolerance for high magnification performance is about 0.6mm or 0.02-inch. Although this sounds very critical, all of the alignments discussed above magnify the error 2X, which means the allowable tool deviation is 0.04-inch. If your alignments fall within this tolerance, you can choose to use the alignment as is, or you can investigate further to determine the cause of the mismatch.

#238 LcJ

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Posted 07 December 2008 - 06:40 PM

Jason,
I don't think it is the bow tie (but I used to wear those a lot!).

Vic, I have wondered why many times. My scope is a 10" f4.9

I got the glatter and the blug. Set everything up about as good as I could. I would imagine that my triangle is a little off, but not by much. Now could the actual focal center of the mirror be off. I would imagine that also. Once I got the Catseye AC I just had to have it all lined up. Well, as soon as I think I do, I apparently don't. Bought Vic last book and try everything I can think of so I think I am just going back to blugging it. But this stuff is interesting to say the least and frustrating at times. Once I get all four little images lined up, I will take the AC out and check the blug and it is off. When I put the AC back in without doing anything, it is off again.

Could I have gremlins in the scope? :)

I hope not.

Thanks for the responses,
Lyle

#239 Howie Glatter

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Posted 07 December 2008 - 07:14 PM

Vic said: "The big question is why the error isn't visible using the Blug, which also works just like a Cheshire eyepiece (or collimation cap). To find out, try rotating both tools. If the pupil moves when you test the AC, you've found the problem. If the Barlow/emitter moves when you rotate the Blug, that's the problem. If you're using a 2- to 1.25-inch adapter with one tool and the other is a 2-inch tool, that could be the problem. Or you may find you have more than one problem that's keeping the two tools from showing good alignment simultaneously. "

That is a good strategy for diagnosing the problem. You should assess:
1. The repeatability of registration of the tools in the focuser drawtube, and if there is drawtube play. If there is any "wiggle" at all of the tool in the drawtube or the drawtube in the focuser with moderate pressure on the tools in all directions, that's a problem
2. The tool accuracy. Rotate and re-clamp the laser collimator, and the autocollimator, and assess if the resultant read remains identical. With the Blug, rotate it to different orientations in the drawtube, making sure it is seated each time against the drawtube inner end, and check the shadow position on the screen each time.

If the problem is the collimator or the Blug, I plan to shoot myself in front of the assembled entire Cloudy Nights membership.

Best wishes, Howie

#240 Howie Glatter

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Posted 07 December 2008 - 07:18 PM

"I plan to shoot myself in front of the assembled entire Cloudy Nights membership."

I meant with a can of whipped cream.

H.

#241 Vic Menard

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Posted 07 December 2008 - 07:27 PM

I don't think it is the bow tie (but I used to wear those a lot!).

If you're using the iterative method, it could indeed be a close jumble that resolves into two axes that intersect at the ROC. This would look like a perfect stack, but would not agree with the Blug (which would show the residual primary mirror axial error). If you correct the primary with the Blug, the autocollimator will again show a close jumble, which you can further reduce by adjusting the secondary (and if you get a "perfect" stack, it's actually quite likely you've realigned the axes again so they intersect at the ROC!) Each iteration reduces both axial errors until both tools show "perfect" alignment.

If you carefully decollimate the primary mirror first, and stack the fainter inverted reflection with the front most upright reflection, you zero the focuser axis first. and you can then align the primary mirror without affecting the focuser axial alignment--one step!

Vic, I have wondered why many times. My scope is a 10" f4.9

That's a more generous tolerance than f/4.7. At f/4.9, the primary mirror axial tolerance is 0.65mm or about 0.025-inch (0.05-inch tool tolerance).

I would imagine that my triangle is a little off, but not by much.

Even if it is off--it won't affect the tool alignment.

Now could the actual focal center of the mirror be off.

Although that would affect your scope's performance, it has no impact on the tools.

Bought Vic last book and try everything I can think of...

Did you try the carefully decollimated primary procedure?

...so I think I am just going back to blugging it.

If you can't get the tools to agree, and you've verified the Blug by rotating the Blug in the focuser drawtube, you should use the Blug result until you've resolved what's impacting the AC alignment.

But this stuff is interesting to say the least and frustrating at times. Once I get all four little images lined up, I will take the AC out and check the blug and it is off. When I put the AC back in without doing anything, it is off again.

Without doing anything? That sounds like a registration issue...

Could I have gremlins in the scope? :)

Unless you've already exorcised them, it's a given with most assembly line scopes! Looks like you've already addressed the optics--but the compression ring in the focuser could be a problem, and two locking screws can play havoc with the focuser axis...

#242 auriga

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Posted 07 December 2008 - 07:39 PM

...As the thread indicates, an autocollimator provides a clarity and simplicity that will appeal to novices, particularly those with engineering or physics backgrounds.

Using the same logic, understanding how a laser works may also appeal to "those novices with engineering or physics backgrounds". Of course, you don't need to know how a laser collimator works to use one. Similarly, you don't need to know how an autocollimator works to use one with the CDP procedure--which does, in fact, clearly show both axial alignments and simplifies their reduction.

Unfortunately, you're unlikely to find an Infinity XL or a Glatter laser in the hands of a novice. They'll more likely be drawn to the one-step simplicity of an inexpensive windowed laser or perhaps an improper alignment procedure that leaves the focuser axis and/or the secondary mirror alignment for CN contributors to resolve in another lengthy offset and/or skew discussion.

Axial alignment is easy--whether your tool of choice is a Glatter laser or a Catseye autocollimator.


Vic,
Speaking of novices, I had the impression, before reading this thread, that first one should make sure the focuser is square to the tube, shimming it if it is not, then one should use a sight tube to make sure the diagonal is properly situated under the focuser. Then one collimates both the diagonal and the primary with a Cheshire (which may be combined with a sight tube).

I was under he impression that, in the sequence given above, if one uses a barlowed laser instead of the Cheshire, the advantage was convenience, not accuracy.

In the sequence given above, is the Cheshire sufficiently accurate? Or is an autocollimator needed as a check on the Cheshire?

I had the impression from Nils Olaf Carlson's web pages that his view is, when the Cheshire and the autocollimator disagree, choose the Cheshire.

Would a novice be okay using a sight tube plus Cheshire?


Bill Meyers

#243 Vic Menard

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Posted 07 December 2008 - 07:42 PM

...You should assess:
1. The repeatability of registration of the tools in the focuser drawtube, and if there is drawtube play. If there is any "wiggle" at all of the tool in the drawtube or the drawtube in the focuser with moderate pressure on the tools in all directions, that's a problem.

It's not uncommon to see some minimal unstacking related to the focuser mechanics and tool registration with the autocollimator under such a test. But the alignment should "spring back" to the perfect stack until the set screw tension is released--then the reflections can be unstacked easily (it's how I usually demo a "perfect" stack).

2. The tool accuracy. Rotate and re-clamp the laser collimator, and the autocollimator, and assess if the resultant read remains identical. With the Blug, rotate it to different orientations in the drawtube, making sure it is seated each time against the drawtube inner end, and check the shadow position on the screen each time.

Just thinking out loud. The Blug has no set screw, but uses compression, in effect, a self-centering alignment. Depending on the amount of lateral offset caused by tightening the focuser locking screw, there could be a small discrepancy between the two tools (in fact, between the Blug and the self-Barlow or 1mm aperture stop accessories).

I wonder... :question:

#244 LcJ

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Posted 07 December 2008 - 08:04 PM

Howie,
I can seat your 2" Glatter in the Moonlite and center the 1mm spot and rotate and it doesn't vary (if I have indeed seated it properly) and then collimate the blug till everything looks centered and rotate it and it is not noticeable to my eyes (of course my eyes might be another problem all together). Then I stick in the Catseye AC and the off centered pupil is fixed. Even when I rotate the AC. If all four are lined up in one, the stay hidden. If there are more than one visible, they stay in the same position through rotation as does off center pupil.

But I wouldn't worry about getting the whipped cream unless......(I will quit there)

It might be all me and my eyes. I wear contacts and without them I am pretty muchly non functional (glasses help also, but everything at the edge is soooo curved).

I don't think I have that big of a problem because I can see m1 easily (or is that a droplet of snot on my lens? or a very small ghost?). But hey, I just want it to do what it should. Kind of a puzzle.

Like I said I have tried everything I can think of. Have pulled the mirror cell out and line up the secondary with the holographic attachment, several time. Used the Catseye sight tube till I'm blue in the face.

Should I also confess that being born and bred in Mississippi I might be a little slow. :)

Thanks for reading.

Lyle

#245 Vic Menard

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Posted 07 December 2008 - 08:06 PM

...Speaking of novices, I had the impression, before reading this thread, that first one should make sure the focuser is square to the tube, shimming it if it is not, then one should use a sight tube to make sure the diagonal is properly situated under the focuser. Then one collimates both the diagonal and the primary with a Cheshire (which may be combined with a sight tube).

I agree with you, and believe me, getting that diagonal properly situated under the focuser is much harder than axial alignment!

I was under he impression that, in the sequence given above, if one uses a barlowed laser instead of the Cheshire, the advantage was convenience, not accuracy.

I'm not sure about convenience (unless you're referring to a Blug or tuBlug to minimize traveling back and forth from one end of the scope to the other to correct the primary mirror alignment), I would say personal preference. The fact that the Barlowed laser is parallax free is a plus, but then the Cheshire eyepiece allows you to view the alignment from the focuser axis...

In the sequence given above, is the Cheshire sufficiently accurate? Or is an autocollimator needed as a check on the Cheshire?

Used properly, it's certainly accurate enough for the primary mirror axial alignment. Depending on the aperture and whether or not coma correction is used, it may not be accurate enough for focuser axial alignment (although the Glatter with 1mm aperture stop should be). Used for redundant verification, if you have a quality laser like the Glatter you should quickly reach a level of expertise that delivers a perfect stack fairly often. If you can't, you may not want to put your AC away yet...

I had the impression from Nils Olof Carlin's web pages that his view is, when the Cheshire and the autocollimator disagree, choose the Cheshire.

I think I just said the same thing two posts back.

Would a novice be okay using a sight tube plus Cheshire?


If his optics are f/6 or longer, and he uses the tools properly, he might even find that his 8-inch Newtonian can outperform his high-end 4-inch refractor. :ubetcha:

#246 Starman1

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Posted 07 December 2008 - 08:28 PM

At this point it might be helpful to remind people that chasing perfection with collimation tools assumes a mechanical stiffness sufficient to hold collimation.
I've listed the problems I went through to attain adequate stiffness in other posts in other threads, but suffice it to say you are doomed to failure in collimation unless:
--the primary doesn't move when you change the position of the scope
--the secondary spider vanes don't flex when the mirror goes from underneath the spider (zenith) to beside the spider (horizon)
--the poles don't sag under the weight of the UTA
--the mechanical linkages don't move
--the focuser doesn't sag (indicating a loose drawtube--a common problem)
--the focuser board doesn't flex

One of the amusing side effects of the autocollimator's persnicketyness is watching the stack of 4 centermarks come unstacked and wander all over the place as my truss poles cool down, only to reunite in a perfect stack once all the poles have achieved thermal equilibrium. I used to recollimate 4 or 5 times during that first hour of precipitous temperature drop at my favorite site, only to realize I was chasing the differential lengths of the poles as they cooled. Now I wait until the temperature drop slows down and check it again. I've found that a careful collimation when it's warmer usually means collimation is either perfect or close enough once it gets colder. This could equally apply to those of you with steel tubes if you collimate immediately after taking your scope from a warm house to a colder outside.

#247 Vic Menard

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Posted 08 December 2008 - 09:59 AM

...I can seat (the) 2" Glatter in the Moonlite and center the 1mm spot and rotate and it doesn't vary (if I have indeed seated it properly) and then collimate the blug till everything looks centered and rotate it and it is not noticeable to my eyes (of course my eyes might be another problem all together). Then I stick in the Catseye AC and the off centered pupil is fixed. Even when I rotate the AC. If all four are lined up in one, the stay hidden. If there are more than one visible, they stay in the same position through rotation as does off center pupil.

I suspect it's the Blug operating in a "self centering" mode where the other tools (and your eyepieces) operate with a small lateral offset when the focuser locking screw is tightened. You can verify this with the new 1mm aperture stop by assessing the alignment of the center spot silhouette embedded in the diffraction rings on the target face of the aperture stop (it works just like the Barlowed laser).

It might be all me and my eyes. I wear contacts and without them I am pretty muchly non functional (glasses help also, but everything at the edge is soooo curved).

Try the 1mm aperture stop to assess both axial alignments right at the end of the laser! First, decollimate the primary mirror a bit to move the silhouette of the center spot away from the 1mm hole in the aperture stop so you can clearly see the silhouette and the return laser dot and diffraction pattern. Next, adjust the secondary mirror tilt to align the laser dot/diffraction pattern with the silhouette (you won't need to go back and forth between the primary mirror and the laser, you can do it all at the laser). Take your time and get the dot/diffraction pattern "perfectly" aligned with the silhouette. Then recollimate the primary mirror so the silhouette/laser dot/diffraction pattern are perfectly aligned to the 1mm hole in the aperture stop. If you take your time to get the 1mm aperture stop alignments right, you'll find that the autocollimator will often show a perfect stack with no further adjustment.

I don't think I have that big of a problem because I can see m1 easily...

I doubt that you're using very high magnification on M1. Now if you can see detail in the cloud bands on Saturn...

Like I said I have tried everything I can think of. Have pulled the mirror cell out and line up the secondary with the holographic attachment, several time. Used the Catseye sight tube till I'm blue in the face.


Persistence pays off.
I think you're doing everything right, you just have a discrepancy between the Blug and the autocollimator. If I'm not mistaken, I think you'll find you have a discrepancy between the Blug and the 1mm aperture stop (using the Barlowed laser procedure) too.

Let us know what you find...

#248 LcJ

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Posted 08 December 2008 - 10:17 AM

Try the 1mm aperture stop to assess both axial alignments right at the end of the laser! First, decollimate the primary mirror a bit to move the silhouette of the center spot away from the 1mm hole in the aperture stop so you can clearly see the silhouette and the return laser dot and diffraction pattern. Next, adjust the secondary mirror tilt to align the laser dot/diffraction pattern with the silhouette (you won't need to go back and forth between the primary mirror and the laser, you can do it all at the laser). Take your time and get the dot/diffraction pattern "perfectly" aligned with the silhouette. Then recollimate the primary mirror so the silhouette/laser dot/diffraction pattern are perfectly aligned to the 1mm hole in the aperture stop. If you take your time to get the 1mm aperture stop alignments right, you'll find that the autocollimator will often show a perfect stack with no further adjustment.



This I will try, hopefully today.

Persistence pays off.
I think you're doing everything right, you just have a discrepancy between the Blug and the autocollimator. If I'm not mistaken, I think you'll find you have a discrepancy between the Blug and the 1mm aperture stop (using the Barlowed laser procedure) too.

Let us know what you find...



I hope Persistence pays off and I will let you know.

Oh, I have seen M1 and Saturn with a 5mm which is about 250X and I don't think I have ever seen any detail, but then that was last year and I think I am actually catching more detail this year. Time also makes a difference.

Thanks for the suggestions. All good info.

#249 LcJ

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Posted 08 December 2008 - 04:55 PM

Persistence pays off.
I think you're doing everything right, you just have a discrepancy between the Blug and the autocollimator. If I'm not mistaken, I think you'll find you have a discrepancy between the Blug and the 1mm aperture stop (using the Barlowed laser procedure) too.

Let us know what you find...



Puzzled and amazed and how simple life can be....at least for now. At lunch, went home and plugged in the Glatter with the 1 mm stop and centered it as carefully as I could in the focuser and then centered the laser in the triangle with the secondary screws and then got the little red rabbit back in the hole it came out of with the primary knobs and it appeared that there were concentric circles (similar to a star collimation) around the center hole of the 1mm. Then put in the Blug and it was centered (or very close to such). Put in the Catseye AC and it was the best image I've seen. Everything seemed centered and no ghost triangles. Then put in the TuBlug and it was also giving a good test. Now to mess it all up tonight and try it again. It seems that if I can do it repeatedly all with the 1 mm stop, then all this will seem very simple. I wonder how easy it would be to see the 1mm stop from the back of a truss, maybe even in the secondary?

Thanks a beaucoup (a red neck cajun variation of a bunch).

Seek and ye shall find and ask and it shall be given unto you. Yeah Vic....the messenger.

#250 Joe G

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Posted 08 December 2008 - 06:45 PM

Well, I agree that this has been a great discussion. So much so that I spent a couple of hours re-reading it.

One thing pops into mind is that it surely would be interesting if someone could program a "virtual" reflector animation/program where you could learn to collimate by computer. Maybe show a cross section of a reflector and the views from the various tools with virtual primary and secondary knobs (and maybe the spider adjustments). These could be shown on the same screen so that the user could, say, tweak the primary collimation screws and see how that would change the view in a cheshire or autocollimator.

You could mess up the collimation and practice tweaking it to achieve perfect collimation while the computer screen shows various points of view (the cross section of the reflector, the cheshire and the autocollimator). This could be done with either the Catseye system tools and/or laser/barlowed laser tools. The program could run a script which would run through the steps needed and show the views thru the various tools and how they change as you are tweaking in real time.

If it was fancy enough, it would trace light rays in another window showing some of the stuff Jason did. The views thru the cheshire/autocollimator would look like Jim's POV-ray animations.

Just a thought.

Although I'd hate to see the end of these discussions if the program worked too well!


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