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Equipment Discussions >> Reflectors

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auriga
Pooh-Bah


Reged: 03/02/06

Another innovation from Howie Glatter?
      #5926663 - 06/18/13 12:04 AM

We all know that this inventive genius has given us the best laser collimator, and the Blug, the tuBlug, mounts for laser pointers, supporting attachments for Obsession-type mirror straps, and the Parallizer for optical alignment.

What is next from Howie? One I have been awaiting impatiently may have been seen briefly in a video at NEAF 2013. If and when it gets to market it will be a great boon to reflector users.

I am waiting and hoping.

Any word, Howie?

Bill Meyers


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Howie Glatter
Vendor


Reged: 07/04/06

Re: Another innovation from Howie Glatter? new [Re: auriga]
      #5927132 - 06/18/13 09:54 AM

O.K. Bill, no big secret - I'm working on a Newtonian secondary mirror mount idea, that, to my surprise, someone already posted a picture of in a thread here. He took the picture at NEAF this year, but I've had that prototype installed in my scope for a few years. The idea does not have to do so much with this particular "embodyment" (patent lawyer-speak) of the holder, but with the principle of motion of the adjustments. In my opinion, the adjustment axis of most conventional Newtonian secondary holders are slightly insane.

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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: Another innovation from Howie Glatter? new [Re: Howie Glatter]
      #5927155 - 06/18/13 10:09 AM

"In my opinion, the adjustment axis of most conventional Newtonian secondary holders are slightly insane."

...and we all know Howie isn't "slightly" anything.....When Howie does it, he goes all out and his products show it...Keep up the great work...


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Starman1
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Reged: 06/24/03

Loc: Los Angeles
Re: Another innovation from Howie Glatter? new [Re: csrlice12]
      #5927253 - 06/18/13 10:59 AM Attachment (125 downloads)

Howie,
A few years ago, I created a device for my secondary mirror that allowed extremely fine rotation of the secondary around its center bolt axis. It was a small device that attached to the center bolt and anchored on a spider vane.
I used it until my understanding of collimation grew to understand that the secondary did not have to be absolutely perfectly rotated in order to collimate a scope. Just eyeballing the rotation was good enough to achieve near-perfect collimation.
It worked like a tangent arm on a declination axis.
Here is a "back of the envelope" drawing:


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Howie Glatter
Vendor


Reged: 07/04/06

Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5927386 - 06/18/13 12:01 PM

Hi Don,

That's a good design for precise rotation adjustment. I've envisioned something like that to rotate the far ends of the vanes to square them with the optical axis.

With my mount design, I'm trying to eliminate the need to re-adjust the rotation of the holder once it is initially set.


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dscarpa
Post Laureate
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Reged: 03/15/08

Loc: San Diego Ca.
Re: Another innovation from Howie Glatter? new [Re: auriga]
      #5927395 - 06/18/13 12:05 PM

The secondary alignment was what drove me to madness with the newts I had 35 years ago, The primaries were easy. When I tried to tighten the secondary screws after getting everything lined up just right it would shift. If the 3 screw 3 vane spider on my soon to be here Tetter STS has the same issue I'll be in the market for something else. As is I'm looking forward to using Howie's laser and barlow plug bought used on CNC. David

Edited by dscarpa (06/18/13 12:08 PM)


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howard929
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Reged: 01/02/11

Loc: Low End of High Ground
Re: Another innovation from Howie Glatter? new [Re: dscarpa]
      #5927444 - 06/18/13 12:31 PM

Since the ends of secondary adjustment screws make contact with the back of the secondary mirror holder, turning the screws to make tilt adjustments tends to cause the holder to rotate. It's bad by design. Milk jug washers seem to work well unless or until they become too rutted out. FWIW, I'm getting by with a slippery washer between the holder and the screws that does rotate somewhat during tilt adjustments but slides against the holder which doesn't rotate. All of this is helped by rounding the screw ends smooth and snugging them down as opposed to really tight.

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turtle86
Pooh-Bah Everywhere Else
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Reged: 10/09/06

Re: Another innovation from Howie Glatter? new [Re: Howie Glatter]
      #5927527 - 06/18/13 01:24 PM

Quote:

O.K. Bill, no big secret - I'm working on a Newtonian secondary mirror mount idea, that, to my surprise, someone already posted a picture of in a thread here. He took the picture at NEAF this year, but I've had that prototype installed in my scope for a few years. The idea does not have to do so much with this particular embodyment (patent lawyer word)of the holder, but the principle of motion of the adjustments. In my opinion, the adjustment axis of most conventional Newtonian secondary holders are slightly insane.




I would definitely welcome anything that would make tweaking the secondary during collimation easier. I particularly find it a bit of a challenge to make those minute adjustments to the secondary screws when using my autocollimator.


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acochran
professor emeritus


Reged: 06/19/08

Loc: So. CA
Re: Another innovation from Howie Glatter? new [Re: Howie Glatter]
      #5928004 - 06/18/13 05:49 PM

Howie: I'm hoping for a spider that reduces/eliminates collimation drift when moving telescope tube from vertical to horizontal.
Andy


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jpcannavo
scholastic sledgehammer
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Reged: 02/21/05

Loc: Long Island New York
Re: Another innovation from Howie Glatter? new [Re: acochran]
      #5928060 - 06/18/13 06:44 PM

Howie
Slightly insane is exactly right. It crazy how backward some things remain! I do remember looking at your design at NEAF this year. I look forward to its emergence on the market.

Andy
As for collimation drift. This whole approach where the secondary is perched on some bolt, displaced along the axis of the truss/tube from the spider vanes, is crazy as well. It sets up a moment arm that must slightly torque the veins, introducing shift. There are surely ways to get around this that would sill allow some back and forth adjustment of the secondary along said axis. Howie get busy on that as well! ( I plan to when my shop is reconstituted in Denver!)

Joe


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BlackBirdCD
member


Reged: 08/19/12

Loc: Pacific Northwest
Re: Another innovation from Howie Glatter? new [Re: Howie Glatter]
      #5928148 - 06/18/13 07:33 PM

Quote:

With my mount design, I'm trying to eliminate the need to re-adjust the rotation of the holder once it is initially set.




THANK YOU!


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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Another innovation from Howie Glatter? new [Re: howard929]
      #5928334 - 06/18/13 09:58 PM

Quote:

Since the ends of secondary adjustment screws make contact with the back of the secondary mirror holder, turning the screws to make tilt adjustments tends to cause the holder to rotate. It's bad by design. Milk jug washers seem to work well unless or until they become too rutted out. FWIW, I'm getting by with a slippery washer between the holder and the screws that does rotate somewhat during tilt adjustments but slides against the holder which doesn't rotate. All of this is helped by rounding the screw ends smooth and snugging them down as opposed to really tight.




There are only two adjustments needed for a secondary - a rotational one to make it aligned flat with the focuser, and a one-axis tilt. Only a single tilt adjustment screw should exist. My secondary holder from Astrosystems has four screws, three too many (in a proper design).

We need secondary holders that just do these two collimation adjustments.


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davidpitre
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Reged: 05/10/05

Loc: Central Texas
Re: Another innovation from Howie Glatter? new [Re: jpcannavo]
      #5928438 - 06/18/13 11:34 PM

Quote:



This whole approach where the secondary is perched on some bolt, displaced along the axis of the truss/tube from the spider vanes, is crazy as well. It sets up a moment arm that must slightly torque the veins, introducing shift. There are surely ways to get around this that would sill allow some back and forth adjustment of the secondary along said axis.



Agreed. I see these huge honkin secondaries hanging from an extended bolt, and just shake my head.
John Pratte of JP Astrocraft has designed a secondary holder that solves some of these problems.


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csrlice12
Postmaster
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Reged: 05/22/12

Loc: Denver, CO
Re: Another innovation from Howie Glatter? new [Re: careysub]
      #5928441 - 06/18/13 11:35 PM

Just a question, why can't the secondary be mounted to the focuser itself? It would seem at least on high end equip to be more stable....

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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Another innovation from Howie Glatter? new [Re: csrlice12]
      #5928460 - 06/18/13 11:50 PM

I find my f/9 secondary can be a pain in the neck. At f/4 or 5....!i don't envy you guys! If Howies got something new going on here it'd be a nice thing.

Pete


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FirstSight
Duke of Deneb
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Reged: 12/26/05

Loc: Raleigh, NC
Re: Another innovation from Howie Glatter? new [Re: azure1961p]
      #5928569 - 06/19/13 01:08 AM

I have a Protostar secondary holder, and don't seem to have the sorts of torque/rotation problems people describe above. Each of the three adjusting screws sits against a sort of clutch mechanism between its end and the actual holder that functions like a more sophisticated, improved version of the washer idea mentioned above. This "clutch" design (how Brian Geer of Protostar describes it) also has the benefit of making adjustments to any one screw far more independent of adjustments to the other two, i.e. it substantially reduces how often you first need to loosen one screw before you can tighten another.

I think I get in principle why carysub above says you only need a rotational tilt adjustment plus a one-axis tilt adjustment, but IMHO it's much easier to make tilt adjustments to nail collimation dead-on with an autocollimator if you have three tilt adjustment screws. I really don't having three tilt adjustment screws to be any significant impediment at all with the Protostar design.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Another innovation from Howie Glatter? new [Re: careysub]
      #5928692 - 06/19/13 05:28 AM

Quote:

There are only two adjustments needed for a secondary - a rotational one to make it aligned flat with the focuser, and a one-axis tilt. Only a single tilt adjustment screw should exist. My secondary holder from Astrosystems has four screws, three too many (in a proper design).

We need secondary holders that just do these two collimation adjustments.




I had a secondary mount like that once.. it used a hinge.

I would like to see Vic, Jason and Nils comments, particularly in light of Don's comments. With a 2 dimensional tilt adjustment that we all use, I believe small rotations are part of the adjustment process.

Securing/locking the rotation of the secondary is mechanically more difficult than securing the tilt, as long as collimation adjustments represents a small variations, it's not clear to me that a secondary rotation adjustment is an advantage.

"In theory there is no difference between theory and practice. In practice, there is.

Yogi Berra"

Jon Isaacs


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Starman1
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Reged: 06/24/03

Loc: Los Angeles
Re: Another innovation from Howie Glatter? new [Re: Jon Isaacs]
      #5929046 - 06/19/13 11:28 AM

For each rotational angle of the secondary, there is a tilt angle that results in axial collimation. Once you realize that, you realize there are only a couple reasons to try to rotate the secondary to appear round under the focuser:
--it reduces tilt in the final focal plane to a level we won't notice
--it results in the best edge of field illumination for the short axis of the secondary's ellipse.

That means that a device to make fine rotations of the secondary is unnecessary. Not bad, merely unnecessary. You can do it by eye by simply making the secondary as round as you can get it when looking through the focuser and by centering the reflected image of the primary in the short-axis dimension.

The autocollimator-derived secondary adjustments needed after that are really minor.

The push-push antagonistic screw secondary adjustment could be replaced with a single threaded screw and a hinge. But I think the system needs at least two dimensions for adjustment. When using the autocollimator to reduce residual secondary error, I always have to adjust screws on more than one axis. The amount is tiny, but I always adjust on at least two axes. One of the advantages of the 4-screw secondary is that I can also turn pairs of screws and adjust not only the N-S, and E-W axes, but also the NW-SE and NE-SW axes if needed.


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5929073 - 06/19/13 11:44 AM

Quote:

For each rotational angle of the secondary, there is a tilt angle that results in axial collimation. Once you realize that, you realize there are only a couple reasons to try to rotate the secondary to appear round under the focuser:
--it reduces tilt in the final focal plane to a level we won't notice
--it results in the best edge of field illumination for the short axis of the secondary's ellipse.

That means that a device to make fine rotations of the secondary is unnecessary. Not bad, merely unnecessary. You can do it by eye by simply making the secondary as round as you can get it when looking through the focuser and by centering the reflected image of the primary in the short-axis dimension.

The autocollimator-derived secondary adjustments needed after that are really minor.

The push-push antagonistic screw secondary adjustment could be replaced with a single threaded screw and a hinge. But I think the system needs at least two dimensions for adjustment. When using the autocollimator to reduce residual secondary error, I always have to adjust screws on more than one axis. The amount is tiny, but I always adjust on at least two axes. One of the advantages of the 4-screw secondary is that I can also turn pairs of screws and adjust not only the N-S, and E-W axes, but also the NW-SE and NE-SW axes if needed.




Don:

Thanks for clarifying these issues, basically that is what I was thinking... One could design an rotation adjustment so that it could be used along with a single tilt adjustment.

In making fine adjustments, using two screws that are antagonistic, that is pushing against each other as in the 4 screw secondary, is an advantage because both screws can be tight and the final adjustment is just to one of them. You are using the mounting as a spring, flexing it slightly. Any tilt adjustment needs two screws for this reason.

A rotation adjustment could be done in a similar fashion, a lever with two antagonistic screws.. But locking a rotation generally requires clamping and that can induce rotation.

Jon


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davidmcgo
Pooh-Bah
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Reged: 10/09/04

Loc: San Diego, CA
Re: Another innovation from Howie Glatter? new [Re: Jon Isaacs]
      #5929131 - 06/19/13 12:29 PM

Would going to a single tilt srew and rotation assume the spider is exactly perpendicular to the tube?

Dave


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Jon Isaacs
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Reged: 06/16/04

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Re: Another innovation from Howie Glatter? new [Re: davidmcgo]
      #5929162 - 06/19/13 12:52 PM

Quote:

Would going to a single tilt srew and rotation assume the spider is exactly perpendicular to the tube?

Dave




Dave:

I think it does work but from a practical viewpoint, it's not clear to me it's an advantage.

Jon


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mtb54703
professor emeritus
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Reged: 11/12/08

Loc: Eau Claire, WI
Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5929322 - 06/19/13 01:58 PM

Quote:

For each rotational angle of the secondary, there is a tilt angle that results in axial collimation. Once you realize that, you realize there are only a couple reasons to try to rotate the secondary to appear round under the focuser:
--it reduces tilt in the final focal plane to a level we won't notice
--it results in the best edge of field illumination for the short axis of the secondary's ellipse.




Question... assuming everything other than the secondary not being exactly round under the focuser is correct - how would this mis-adjustment of secondary manifest itself at the EP? I'm guessing it would show up more with longer EPs/lower power since those make the most use of the FIF.


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Starman1
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Reged: 06/24/03

Loc: Los Angeles
Re: Another innovation from Howie Glatter? new [Re: mtb54703]
      #5929385 - 06/19/13 02:20 PM

Quote:

Quote:

For each rotational angle of the secondary, there is a tilt angle that results in axial collimation. Once you realize that, you realize there are only a couple reasons to try to rotate the secondary to appear round under the focuser:
--it reduces tilt in the final focal plane to a level we won't notice
--it results in the best edge of field illumination for the short axis of the secondary's ellipse.




Question... assuming everything other than the secondary not being exactly round under the focuser is correct - how would this mis-adjustment of secondary manifest itself at the EP? I'm guessing it would show up more with longer EPs/lower power since those make the most use of the FIF.



Sure. Let's imagine a serious mis-rotation of the secondary, with the secondary rotated until it appears oval. You still can adjust the tilt to put a laser beam on the center of the primary (though the secondary holder won't be in line with the tube). The top of the image would be farther from the eye than the bottom of the image and there would be a substantial tilt to the focal plane. Focus would be a line across the field, with the top of the field needing additional infocus and the bottom of the field needing outfocus.
Larger fields of view would show it worse, you are correct.

Now, let's adjust the secondary until it's round to the eye and the reflected image of the primary is centered and concentric. We could still be a little off, but the angular error would be small. Tilt of the secondary to line up the focuser axis with the center of the primary would result in only a tiny amount of secondary movement. And the tilt in the final focal plane would be less than our eyes' ability to accommodate mis-focusing. There would be a range of rotation of the secondary where this would apply, but assuming the initial centering of the secondary using a sight tube and a concentric primary reflection, you would be within that range.

Which is why extremely fine rotation of the secondary in collimation is not necessary. But at least two axes of tilt will be necessary to adjust out residual errors with the autocollimator. So the idea of having only one axis of adjustment and rotation sounds reasonable, but in practice you need two axes of adjustment.

I'm a little more of a perfectionist, and I appreciate having 4 axes of adjustment + rotation. Even if I don't use all those adjustments all the time.


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Vic Menard
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Reged: 07/21/04

Loc: Bradenton, FL
Re: Another innovation from Howie Glatter? new [Re: Jon Isaacs]
      #5929425 - 06/19/13 02:38 PM

Quote:

Quote:

There are only two adjustments needed for a secondary - a rotational one to make it aligned flat with the focuser, and a one-axis tilt. Only a single tilt adjustment screw should exist. My secondary holder from Astrosystems has four screws, three too many (in a proper design).




I would like to see Vic, Jason and Nils comments, particularly in light of Don's comments. With a 2 dimensional tilt adjustment that we all use, I believe small rotations are part of the adjustment process.

Securing/locking the rotation of the secondary is mechanically more difficult than securing the tilt, as long as collimation adjustments represents a small variations, it's not clear to me that a secondary rotation adjustment is an advantage.




Secondary mirror tilt that coincides solely with the major axis of the secondary mirror probably best defines what we are trying to do when assessing/correcting the secondary mirror tilt. Three adjustment screws complicate the process by requiring careful attention to the two screws not on the major axis. Four screws provides a more direct two screw tilt adjustment, allowing for the basic tilt/rotation adjustments you're considering. The other two screws in the four screw tilt models (Rick Singmaster's "forbidden screws") cause a tilt effect I refer to as "skew".

So why do we commonly see this additional alignment flexibility? I believe originally it was provided to accommodate "fixed" focusers. Remember buying the accessory skirt that attached to the bottom of the focuser so it would fit the round telescope tube with no gaps? With a fixed focuser, and pretty much a fixed spider (only basic centering adjustment), any residual misalignment of the focuser/spider geometry could still be accommodated.

Modern truss Dobsonians usually have flat focuser mounting boards. Configure the UTA with an adjustable, "leveling" focuser and you're one step closer to getting rid of the skew adjustment screws. Of course, there are several other considerations if you hope to achieve the best (not just the best "available") secondary mirror placement, all of them impacting the geometry associated with the elliptical flat.

In the last decade or so, it's become common practice to use plastic washers to facilitate manual rotation adjustments. This "unlocked" condition means assessing and correcting secondary mirror rotation is now part of the standard collimation process, especially with larger, more massive secondary mirrors. If you hope to use an autocollimator with one-dimensional tilt and rotation secondary mirror adjustment, you'll need fine adjustment capacity on both adjustments.

Getting back to the question at hand, if the geometries are accurate and robust enough, I see no reason not to limit the secondary mirror adjustments. Personally, I would prefer to "lock them out" myself (like Rick Singmaster), and still have them available when a truss tube gets bent or the focuser board gets damp (or overheated in the daytime sun) and suddenly torques.


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Vic Menard
Post Laureate
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Reged: 07/21/04

Loc: Bradenton, FL
Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5929460 - 06/19/13 02:49 PM

Quote:

For each rotational angle of the secondary, there is a tilt angle that results in axial collimation. Once you realize that, you realize there are only a couple reasons to try to rotate the secondary to appear round under the focuser:
--it reduces tilt in the final focal plane to a level we won't notice...



I'm not sure what you mean here.
If the axial alignments are correct, the final focal plane won't be tilted.

Although I have seen seriously skewed (combined tilt/rotation error) secondary mirrors (usually the result of using a simple thin beam laser exclusively for collimation) that delivered anomalous star tests in spite of "good" axial alignment. If the secondary mirror is slightly undersized to minimize CO, this skew error can become visible in star image performance even sooner.


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Vic Menard
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Reged: 07/21/04

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Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5929501 - 06/19/13 03:10 PM

Quote:

Quote:

Question... assuming everything other than the secondary not being exactly round under the focuser is correct - how would this mis-adjustment of secondary manifest itself at the EP?



Sure. Let's imagine a serious mis-rotation of the secondary, with the secondary rotated until it appears oval. You still can adjust the tilt to put a laser beam on the center of the primary (though the secondary holder won't be in line with the tube). The top of the image would be farther from the eye than the bottom of the image and there would be a substantial tilt to the focal plane. Focus would be a line across the field, with the top of the field needing additional infocus and the bottom of the field needing outfocus.
Larger fields of view would show it worse, you are correct.



I haven't seen the focus change you've described when the axial collimation is correct. Although the secondary mirror can appear elliptical and tilted, the flat surface of the secondary mirror still coincides with the intercept plane. And while the optical axis is shifted as you described, the result is similar to that of the new model (except the field illumination can be more profoundly imbalanced).

Quote:

Now, let's adjust the secondary until it's round to the eye and the reflected image of the primary is centered and concentric. We could still be a little off, but the angular error would be small.



What angle are you talking about?

Quote:

Tilt of the secondary to line up the focuser axis with the center of the primary would result in only a tiny amount of secondary movement. And the tilt in the final focal plane would be less than our eyes' ability to accommodate mis-focusing.



Tilting the secondary to align the focuser axis to the primary mirror center spot eliminates focal plane tilt. Or are you suggesting misaligning the focuser axis to improve the secondary mirror placement?

Edited by Vic Menard (06/19/13 03:34 PM)


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Starman1
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #5929711 - 06/19/13 05:14 PM

OK,
I might be missing something here.
If so, I need to be "illuminated".

But axial collimation seems to me to be independent of focal plane tilt.

I'll explain.

Picture a secondary mirror rotated off the correct angle by 30 degrees, with the "top" rotated away from the observer, and the bottom rotated closer.
A laser hitting the secondary would reflect upward, above the primary mirror. The light cone from the primary would reflect to hit a point above the focuser.
But, the secondary could be tilted down to put the laser beam dead center on the primary and still have the 30 degree rotational error.

The return beam of the laser would return to its source.
A cheshire would show the primary's center marker in the center of the tool.

YET, the cone of light from the primary, hitting the secondary, would be reflected into the focuser properly. From the primary's center marker position, I believe the secondary would not appear round, but I am not sure about that.

BUT, the part of the light cone hitting the top of the secondary would have to travel farther to reach the same place above the focuser's drawtube than the part of the light cone hitting the bottom of the secondary. In essence, though the axial beam is perfectly aligned, and collimation can be achieved, the final focal plane would be tilted at the focuser since the focal length of the mirror is identical from all points on the mirror.

Would the axial beam still reflect from a point on the long axis of the elliptical secondary? I don't know, but the focal plane would not be perpendicular to the axis of the focuser. It would be similar in shape to how the secondary appears from the focuser, and tilted to the observer.

If what I just described is not correct, then what's the point of trying to get rotation correct for the secondary mirror? To make the secondary's shroud colinear to the centerline of the tube just to get a round shadow?

It seems to me that as we rotate the secondary mirror we are making all the rays reflecting from the primary mirror come to a focal plane that is perpendicular to the focuser's axis, or as close as we can to it.

But I may be missing something.


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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Another innovation from Howie Glatter? new [Re: Jon Isaacs]
      #5929714 - 06/19/13 05:15 PM

Quote:

...
A rotation adjustment could be done in a similar fashion, a lever with two antagonistic screws.. But locking a rotation generally requires clamping and that can induce rotation.

Jon




But many rotation locking schemes can be imagined where this isn't a problem.

Consider rotation locking using a plate at the upper end of the rotation axle (or a ring attached along it somewhere).

A cam lever when flipped down can provide vertical pressure on the plate or ring that prevents rotation, without creating any torque.

Even a simple screw with a pivoting head could do this, or a screw depressing a leaf spring clamp, or...


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Vic Menard
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Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5929774 - 06/19/13 05:50 PM

Quote:

...Picture a secondary mirror rotated off the correct angle by 30 degrees, with the "top" rotated away from the observer, and the bottom rotated closer.
A laser hitting the secondary would reflect upward, above the primary mirror. The light cone from the primary would reflect to hit a point above the focuser.
But, the secondary could be tilted down to put the laser beam dead center on the primary and still have the 30 degree rotational error.



Yep.

Quote:

The return beam of the laser would return to its source.
A cheshire would show the primary's center marker in the center of the tool.



So far, all true.

Quote:

YET, the cone of light from the primary, hitting the secondary, would be reflected into the focuser properly.



Well, the part of the cone that the secondary intercepts will be reflected into the focuser properly. The part of the cone the secondary misses, will of course, not be reflected.

Quote:

From the primary's center marker position, I believe the secondary would not appear round, but I am not sure about that.



I agree--it will not appear round.

Quote:

BUT, the part of the light cone hitting the top of the secondary would have to travel farther to reach the same place above the focuser's drawtube than the part of the light cone hitting the bottom of the secondary.



No. It may be easier to visualize if you look at the secondary mirror from the center of the focal plane. The mirror surface looks like a skewed ellipse and you can clearly see one side of the secondary mirror holder. If you use a simple thin beam laser, you can see where the laser bounces off the surface of the secondary mirror (it will likely not be in the mechanical center, or the optical center, on the secondary mirror surface). If you were to mark that point and return to the focuser, you would see the point somewhere on the skewed ellipse. You could in fact, mask off a smaller ellipse that is properly aligned to the focuser so that the smaller ellipse appears centered and round. That's because the mirror surface is part of the new intercept plane (defined in part by the change in position of the intersection of the focuser and optical axes).

Quote:

If what I just described is not correct, then what's the point of trying to get rotation correct for the secondary mirror?



To get the maximum balanced illumination with the least diffraction contribution from the CO.


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Starman1
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #5929784 - 06/19/13 05:54 PM

So the only common way to get a focuser plane tilt is to have the focuser axis not correspond to the optical axis?

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Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5929895 - 06/19/13 07:08 PM

Quote:

So the only common way to get a focuser plane tilt is to have the focuser axis not correspond to the optical axis?



Yes.
The focuser axial alignment defines the focal plane perpendicularity.
And the primary mirror axial alignment defines the centering of the coma "free" field diameter in the focal plane.

Optimal secondary mirror alignment ensures the maximum usage of the light cone.


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Jason D
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Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5930156 - 06/19/13 10:02 PM

Quote:

But axial collimation seems to me to be independent of focal plane tilt.







http://www.cloudynights.com/ubbthreads/showthreaded.php/Cat/0/Number/3901098/...


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Nils Olof Carlin
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Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #5930579 - 06/20/13 03:25 AM

Clearly, the focal plane of the primary (it isn't exactly a plane, but...) is perpendicular to the mirror's optical axis. The focal plane of the EP or detector is (hopefully) perpendicular to the focuser axis.
So the focal plane(s!) are not tilted if (and only if) the focuser and primary axes are indeed parallel - and of course preferrably coincident. This is established by the usual methods of axial collimation. This holds even if the secondary is "skewed".

But checking the shape and placement of the actual fully illuminated field is not difficult.
(Put a piece of transparent foil over the focuser opening, at the level of the focal plane. Mark with a Sharpie the line of sight where the primary and secondary seem to touch, at a couple of points to form an ellipse or circle).

Nils Olof


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Re: Another innovation from Howie Glatter? new [Re: careysub]
      #5930659 - 06/20/13 06:26 AM

Quote:

A cam lever when flipped down can provide vertical pressure on the plate or ring that prevents rotation, without creating any torque.




It would probably apply a bending moment though.

Jon


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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #5930661 - 06/20/13 06:29 AM

Quote:

Optimal secondary mirror alignment ensures the maximum usage of the light cone.




Which implies that if the secondary is on the smaller size, this is most important, if it is on the larger size.. not so much???

Jon


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Chucky
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Re: Another innovation from Howie Glatter? new [Re: FirstSight]
      #5930742 - 06/20/13 07:58 AM

<< I have a Protostar secondary holder, and don't seem to have the sorts of torque/rotation problems people describe above. >>

Ditto for me. Never had one bit of a problem. Simply works just fine.


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Re: Another innovation from Howie Glatter? new [Re: Jon Isaacs]
      #5930940 - 06/20/13 09:49 AM

Quote:

Quote:

Optimal secondary mirror alignment ensures the maximum usage of the light cone.




Which implies that if the secondary is on the smaller size, this is most important, if it is on the larger size.. not so much???



For visual applications, a "smaller" secondary may be selected to illuminate a very small field diameter (~0.1-inch) to minimize CO for high magnification performance. In this kind of application, optimal placement of the secondary mirror may be necessary to achieve the desired illuminated field and to minimize anomalous diffraction effects (even in the center of the fov).

Given a slightly oversized secondary mirror, the same effects are still possible, even if they are less visually detectable.


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auriga
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Re: Another innovation from Howie Glatter? new [Re: Nils Olof Carlin]
      #5930976 - 06/20/13 10:08 AM

This is a great discussion and I even understand some of it.

I use a tuBlug and it works very well.

My only problem with collimation is rotation of the diagonal; there is some nut or bolt that governs the rotation, that I need to figure out how to tighten.

But even tightened, I can see how adjusting the collimation screws produces a rotation of the diagonal.

I view the current designs for diagonal adjustment as weird. Three screws with relationships to each other such that tightening one requires loosening the others. The direction of movement of the red laser dot by tightening one screw is orthogonal to the center of the diagonal. Weird.

I have full confidence in Howie Glatter and am impatiently awaiting his invention.

Innovation of any magnitude is often difficult even in amateur astronomy.

There is always resistance.

For years were were told that mass was important in telescope mountings, and people were using massive airplane propeller housings for equatorial mounts. Finally an engineer wrote an article in Sky & Telescope showing mathematically that mass in a mount exerts a bending moment and also torque.

John Dobson submitted an article on his mounting to Sky & Telescope, and the editor rejected it, telling him it would never work.

For years we were told that focal ratios as short as f/6 were a bad compromise, and 8 inch reflectors were manufactured with f/7 and f/8 ratios, and 12.5 inch reflectors were manufactured with f/7 ratios. We were told that very short focal ratios would never work.

There is always resistance. But I am betting on Howie.

Bill Meyers


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Re: Another innovation from Howie Glatter? new [Re: Chucky]
      #5930986 - 06/20/13 10:12 AM

Quote:

<< I have a Protostar secondary holder, and don't seem to have the sorts of torque/rotation problems people describe above. >>

Ditto for me. Never had one bit of a problem. Simply works just fine.




the center bolt and stalk are one piece, and the bolt is used as a spring cause it bends as you adj the tilt so there is always a constant force applied to keep it from rotating.


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Re: Another innovation from Howie Glatter? new [Re: auriga]
      #5931024 - 06/20/13 10:34 AM

Quote:

Innovation of any magnitude is often difficult even in amateur astronomy...

There is always resistance. But I am betting on Howie.



I'm equally amazed at how much innovation we've seen in the past twenty years--computer controlled Dobsonian mounts, slumped, thin blank mirror technology, breaking the f/5, then f/4, and even the f/3 barrier, coma correctors and 100+ degree highly corrected eyepieces, star charts on your cell phone (that use m-theory mathematics to display Near Earth Asteroid motions on the charts), real-time video astronomy and high resolution planetary imaging with DSLRs...the list goes on and on.

Last year I spent some time in an email discussion with Mike Zammit prototyping an upgraded spider hub that provided precise control of the secondary rotation and offset--both away from the focuser and toward the primary mirror! I believe a working prototype exists, although I only saw pictures. I'm not sure why Mike hasn't brought the product to market (probably tooling and the variety of parts required to upgrade the various UTA/spider sizes--while keeping the price competitive)...

Don't get me wrong--Howie's products rock! We're fortunate to have his vision and attention to detail in this era of innovation.


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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #5931087 - 06/20/13 11:08 AM

Normally I'm way out in left field just past the end of the warning track with my take on things...

But isn't all of this secondary mirror tilt exactness predicated on employing the best use of the best AC currently available? With the rest of us who don't have one of those AC's, setting the secondary tilt as a: do it correctly and for the most part, just forget it?


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careysub
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Re: Another innovation from Howie Glatter? new [Re: Jon Isaacs]
      #5931146 - 06/20/13 11:41 AM

Quote:

Quote:

A cam lever when flipped down can provide vertical pressure on the plate or ring that prevents rotation, without creating any torque.




It would probably apply a bending moment though.

Jon




Can you describe the adjustment screw arrangement that does not apply a bending moment anywhere?

In most things mechanical some sort of force has to be applied somewhere to do anything, the question is the load inappropriate for the structural design.


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Re: Another innovation from Howie Glatter? new [Re: auriga]
      #5931167 - 06/20/13 11:59 AM

I remember seeing a secondary in Sky and Telescope new products section a few years ago that had an adjustment system that wouldn't cause the mirror to move when it's tightened down. David

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Re: Another innovation from Howie Glatter? new [Re: howard929]
      #5931188 - 06/20/13 12:18 PM

Quote:

...But isn't all of this secondary mirror tilt exactness predicated on employing the best use of the best AC currently available? With the rest of us who don't have one of those AC's, setting the secondary tilt as a: do it correctly and for the most part, just forget it?



Well, I think we've been describing secondary mirror placement adjustments (rotation and offset/centering), and generally speaking, close enough is good enough. But secondary mirror tilt is commonly used to align (aim) the focuser axis, and for that there are actual tolerances. Depending on the application and whether or not coma correction is used, it can be as small as 0.5-percent of the primary mirror diameter. Even at that level of accuracy, an autocollimator may not be necessary. And if the typical magnification used is moderate (less than about 15X per inch of aperture) and there's no coma correction, the focuser axial tolerance can be quite generous (perhaps as much as 5-percent of the primary mirror diameter).

I'm not so sure about "set it and forget it" though. It's certainly possible, but if you're transporting a truss Dob to a remote site where the larger parts will be reassembled--I think you would at least want to verify the axial alignments (and if the secondary mirror tilt regularly requires adjustment, you may want to periodically assess the secondary mirror placement too)...


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Pinbout
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #5933143 - 06/21/13 02:54 PM

I still like Mark C's design for a secondary holder, strings or not strings. http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Board/atm/Number/25...


it keeps the mirror close to moment of inertia of the structure. very similar to what the people across the water make.

http://strock.pi.r2.3.14159.free.fr/Ast/Strock250/P/S-Araignee.jpg


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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #5933619 - 06/21/13 08:11 PM Attachment (22 downloads)

Hi All,
Not to bust in on the collimation discussion…but after reading the OP I thought I'd show this prototype secondary hub I played with a few years back. It gave you fine adjustment both axial adjustments and rotational. Worked like a charm.

Mike


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michael
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Re: Another innovation from Howie Glatter? new [Re: michael]
      #5933624 - 06/21/13 08:13 PM Attachment (22 downloads)

another angle.

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Happy Birthday audioaficionado
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Re: Another innovation from Howie Glatter? new [Re: michael]
      #5933647 - 06/21/13 08:37 PM

michael how well did it hold up to changes in alt?

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Pinbout
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Re: Another innovation from Howie Glatter? new [Re: michael]
      #5933654 - 06/21/13 08:42 PM

Nice photos of black parts with lots of shadow detail

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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #5933660 - 06/21/13 08:46 PM

Sorry it's all I have.

Mike


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michael
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Re: Another innovation from Howie Glatter? new [Re: audioaficionado]
      #5933674 - 06/21/13 08:52 PM

Changes it altitude have never really been a problem with the secondary...for me anyway. But it held up perfectly. This was with 4”, 4.5” 5”, 5.5” and 6.25” holders. Not sure with anything bigger then that.

Mike


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choran
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Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #6032973 - 08/18/13 02:22 PM

Interesting! I wonder if it would be feasible to concoct a secondary adjustment scheme that utilized a ball joint, like a hip joint. Secondary could be rotated ad well as tilted and then perhaps be locked down with one screw. I have no idea how minute adjustments could be made, however, other than manually, and that probably wouldn't cut it.

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Re: Another innovation from Howie Glatter? new [Re: choran]
      #6033027 - 08/18/13 02:58 PM

I never understood why the secondary can't be made an integral part of the focuser body that extends out over the focuser tube. Only wowld have a single "vane" and adjust on a ball&socket joint and tighten with a screw.....

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Re: Another innovation from Howie Glatter? new [Re: csrlice12]
      #6033343 - 08/18/13 06:12 PM

The thing that gets my pants in a twist is the flex of the thin spider vanes. Collimating is a frustrating exercise in moving the screw, bolt or nut past the correct point and hoping the spider springs back to the right position when you let go.

I totally understand the reason for thin spider vanes but when a force from outside the telescope (i.e. your fingers or a wrench) is applied to anything attached to the spider it moves temporarily out of place.

If a system of tiny motors could be applied to these various screws, bolts and nuts the forces would be applied from inside the structure and there would be no 'spring and rebound' to worry about.

Dave


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CounterWeight
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Re: Another innovation from Howie Glatter? new [Re: csrlice12]
      #6033387 - 08/18/13 06:35 PM

I think in considering alternative designs it's important to think through where the inevitable adjustment(s) is/are made. Are vanes straight and square to tube. Is focuser perfectly perp to tube and center distance perfect for f/l and user focus... and on an on. To me it's more a question of where and how to make up for what, and how close to ideal is reasonable or required for regular consistent use with or without transport and re-assembly.

In the familiar looking secondary adjustment that came with my Orion Dob, it's certainly able to be improved on with a washer. Though the design and tech old, it allows all degrees of XYZ/R freedom in movement to get it placed in the zone simply and quickly and keep it there..

I agree that once there in the zone these type a bit tricky would be nice to have something that remained as easy in fine adjustment but not as prone to unwanted movement. Nice to read about the success with the Protostar.


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Starman1
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Re: Another innovation from Howie Glatter? new [Re: Cotts]
      #6033390 - 08/18/13 06:38 PM

Quote:

The thing that gets my pants in a twist is the flex of the thin spider vanes. Collimating is a frustrating exercise in moving the screw, bolt or nut past the correct point and hoping the spider springs back to the right position when you let go.

I totally understand the reason for thin spider vanes but when a force from outside the telescope (i.e. your fingers or a wrench) is applied to anything attached to the spider it moves temporarily out of place.

If a system of tiny motors could be applied to these various screws, bolts and nuts the forces would be applied from inside the structure and there would be no 'spring and rebound' to worry about.

Dave



Here are some ways to reduce that:
1) remove the spider from the scope and run the collimation screws all the way into and out of the threaded hole several times to eliminate burrs in the threads.
2) De-burr the ends of the screws so the screw end contacting the secondary holder is smooth and/or domed.
3) remove the collimation screws and spray them with a Teflon lube, like Dupont superLube or TriFlow. Let dry and reinstall. The force required to thread the screws in and out should be significantly reduced.
4) Reinstall the spider and significantly tighten the spider attachment screws. If this would cause a dimpling of the tube or UTA where the screws pass through, try adding a fender washer under the screw head to spread the tension over a larger area.
5) if the top of the secondary holder had dimples created by the pressure of the collimation screws, try adding a fender washer to the top of the secondary holder so the screws press on a smooth washer surface instead of the soft materials of the secondary holder.

Edited by Starman1 (08/18/13 06:40 PM)


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SACK
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Re: Another innovation from Howie Glatter? new [Re: csrlice12]
      #6033433 - 08/18/13 07:13 PM

I have thought of that ball and socket design too.
What about a hemisphere shape that is attached to the secondary mirror somehow, rtv, and that hemisphere's center point, (to visualize, like the center of a sphere cut in half but it's center point in relation to the sphere is still the point) landed on the center point of the secondary mirrors offset center point on its surface plane. The hemisphere housing that holds the mirror sits on 3 points.
Once the mirror is centered under the crosshair's of a sight tube, then tilt and rotate with no iterative steps since the pivot point is dead center on the plane of the mirror's surface center point. With other mounts it moves your mirror off to one way or the other and it takes a couple more steps of adjustments to re-align what your initial alignment did. Just rambling off the top of my head, it might not make sense. And I think I overused the word 'point' just now.

One question for anyone, does the tilt action of the secondary along the short axis, I call it side to side, accomplish the same as rotation?


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Re: Another innovation from Howie Glatter? new [Re: SACK]
      #6033549 - 08/18/13 08:30 PM

Quote:

...One question for anyone, does the tilt action of the secondary along the short axis, I call it side to side, accomplish the same as rotation?



Although they look similar when using a simple thin beam laser for assessment/correction--the two alignments are quite different--and using one alignment indiscriminately (for example, tilt when a rotation error needs to be corrected), is the most common cause of combined tilt/rotation alignment error.


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Pinbout
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6033575 - 08/18/13 08:45 PM

How about instead of the collimation screws applying forces some what tanget to the 2ndary face, have them perp to the 2ndary face like a lot of european 2ndary holders.

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Re: Another innovation from Howie Glatter? new [Re: Cotts]
      #6033596 - 08/18/13 08:57 PM

Get rid of the wing nut if you have one and use two standard nuts instead of the one. The first nut on gets a slow and gentle tightening without twisting the spider and the second nut tightens up against the first nut to secure things. I find using this method easier in tightening my 24"'s 5.5" dia. heavy secondary assembly.

Quote:

The thing that gets my pants in a twist is the flex of the thin spider vanes. Collimating is a frustrating exercise in moving the screw, bolt or nut past the correct point and hoping the spider springs back to the right position when you let go.

I totally understand the reason for thin spider vanes but when a force from outside the telescope (i.e. your fingers or a wrench) is applied to anything attached to the spider it moves temporarily out of place.

If a system of tiny motors could be applied to these various screws, bolts and nuts the forces would be applied from inside the structure and there would be no 'spring and rebound' to worry about.

Dave




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Vic Menard
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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #6033608 - 08/18/13 09:01 PM

Quote:

How about instead of the collimation screws applying forces some what tanget to the 2ndary face, have them perp to the 2ndary face like a lot of european 2ndary holders.



I'm pretty sure the two adjustments are still not interchangeable--the screws would have to cause the secondary mirror to move without imparting any tilt, and I don't think that's possible.


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Pinbout
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6033624 - 08/18/13 09:14 PM

but with standard secondary holders we're adj'ing tilt to a plane [top of the stalk] that has nothing to do with the face we care about.

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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #6033658 - 08/18/13 09:33 PM

Quote:

but with standard secondary holders we're adj'ing tilt to a plane [top of the stalk] that has nothing to do with the face we care about.



I know. The best way I can think to visualize the difference is to look at the alignment signatures. With an "ideal" 90-degree intercept, when tilt is correct, you can't see the sides of the secondary mirror regardless of the rotation (rotation happens within a cylinder where the axis of rotation is coincident with the primary mirror axis). If the tilt adjustment allows a side of the secondary mirror to be seen, the final secondary mirror placement will be skewed (combined tilt/rotation error). This is true with offset too.


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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #6033736 - 08/18/13 10:56 PM

Quote:

but with standard secondary holders we're adj'ing tilt to a plane [top of the stalk] that has nothing to do with the face we care about.





To make the tilt plane coincide with the reflective surface of the primary would require a yoke or pivot mechanism to lie along the surface of the mirror. While it could be done, the mechanism would lead to a central obstruction larger than that required by the mirror itself.

It might work better from a collimation perspective, but I think it would be a pretty tough sell to aperture-hungry amateurs.


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Re: Another innovation from Howie Glatter? new [Re: Jeff Morgan]
      #6033743 - 08/18/13 11:01 PM

A lot of european 2ndary's almost do and howie's does as well as mark cowan's, and they don't get in the way

Edited by Pinbout (08/19/13 09:54 AM)


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auriga
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Re: Another innovation from Howie Glatter? new [Re: Howie Glatter]
      #6035647 - 08/20/13 12:00 AM

Quote:

O.K. Bill, no big secret - I'm working on a Newtonian secondary mirror mount idea, that, to my surprise, someone already posted a picture of in a thread here. He took the picture at NEAF this year, but I've had that prototype installed in my scope for a few years. The idea does not have to do so much with this particular "embodyment" (patent lawyer-speak) of the holder, but with the principle of motion of the adjustments. In my opinion, the adjustment axis of most conventional Newtonian secondary holders are slightly insane.




Hi, Howie,
When will I be able to buy one of these?
Bill


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Re: Another innovation from Howie Glatter? new [Re: auriga]
      #6035903 - 08/20/13 06:50 AM

Dear Bill,

> When will I be able to buy one of these?

At the moment the date is uncertain, but I promise that the first announcement to the world will be in the form of a PM to you. Until then, please continue to use your refractor.

Howie


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choran
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6036708 - 08/20/13 03:04 PM

Vic, could you restate or perhaps offer further explanation of this statement:
"With an ideal 90 degree intercept, when tilt is correct you can't see the sides of the secondary mirror regardless of the rotation." I've been following most of the discussion (well, some of it) but this frankly confuses me.
Assume a gross rotational error of, as was posited in an earlier post, 30 degrees or so. It seems to me that regardless of the manner and amount of subsequent corrective tilt, one side of the secondary would in fact be visible. What am I missing?


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Vic Menard
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Re: Another innovation from Howie Glatter? new [Re: choran]
      #6036827 - 08/20/13 04:03 PM

Quote:

...What am I missing?



Clarification (on my part).

Should read, "With an ideal 90 degree intercept, when tilt is correct you can't see the sides of the reflection of the secondary mirror regardless of the rotation."

For example, when looking in a sight tube, the "textbook" presentation for a correctly tilted AstroSystems mounted secondary will reveal the four screw heads that secure the secondary mirror shell to the backplate. This, of course, assumes that the rotation error is not so severe that the reflection of the secondary mirror is no longer visible (and 30 degrees is probably too large). I was assuming a more common starting position--a typical tilt/rotation secondary mirror placement error, usually caused by an error in the focuser/OTA geometry (sometimes referred to as "squaring").

The point I was trying to make is that, if a tilt component moves the secondary mirror enough to make the edge visible (the reflection of the secondary mirror no longer fits inside the cylinder--defined by the minor axis of the secondary mirror and coincident with the optical axis--causing one or more of those screw heads to dip out of view), rotation can't correct the misalignment.

There, that's much clearer!


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Vic Menard
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6036850 - 08/20/13 04:12 PM

It's a similar problem to pursuing an offset secondary mirror alignment with a centered spider. If the focuser is "square" to the OTA and the primary mirror is centered in the OTA, the intercept angle ends up a bit more than 90-degrees and the presentation of the screw heads changes (the secondary mirror is tilted slightly outside of the cylinder).

We could change the "squaring" of the focuser to bring the intercept angle back to 90-degrees (or we could pursue a centered/no offset secondary mirror alignment), but it's pretty common to accept the best available alignment with the given geometries and call it "close enough".


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choran
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6036881 - 08/20/13 04:33 PM

OK, think I've got it now. I appreciate it. I can see all four screw heads, though one appears a bit shallower than the others. If I get all 4 equally visible, not as good a sight tube picture in other respects, so I'll leave it be. I'm chalking it up to gremlins elsewhere. Thanks for the response.

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Starman1
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6036886 - 08/20/13 04:37 PM

Quote:

It's a similar problem to pursuing an offset secondary mirror alignment with a centered spider. If the focuser is "square" to the OTA and the primary mirror is centered in the OTA, the intercept angle ends up a bit more than 90-degrees and the presentation of the screw heads changes (the secondary mirror is tilted slightly outside of the cylinder).

We could change the "squaring" of the focuser to bring the intercept angle back to 90-degrees (or we could pursue a centered/no offset secondary mirror alignment), but it's pretty common to accept the best available alignment with the given geometries and call it "close enough".



Indeed, in the "New Model" of collimation (i.e. unidirectional offset), the reflection angle is slightly greater than 90 degrees and you can't view all the screws on the outside of the secondary holder (in reflection) equally.
If you can, then something else is wrong.


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choran
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Re: Another innovation from Howie Glatter? new [Re: Starman1]
      #6036939 - 08/20/13 05:15 PM

But shouldn't the view of the screws be symetrical, in the sense that perhaps two (and not one) should be shallower? Mind freeze.

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choran
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Re: Another innovation from Howie Glatter? new [Re: choran]
      #6036942 - 08/20/13 05:17 PM

Let me restate that, Starman: Symmetry is not the right word. Wanted to say:
In the case of the "new method", should two of the screws be less prominent, not one?


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Pinbout
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Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6037430 - 08/20/13 10:50 PM Attachment (18 downloads)

here's two different holders.

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Pinbout
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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #6037437 - 08/20/13 10:52 PM Attachment (16 downloads)

and here they are with 30* tilts, both have interference, but I wanted to see how the mirror reacts.

also I uploaded the model so you can check it out.


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Vic Menard
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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #6037830 - 08/21/13 07:43 AM

Thanks for putting up the 3D models. It really makes me appreciate the effort Jim Fly put into POV-Ray for the virtual Newtonian collimation renderings I used in New Perspectives... I don't have SketchUp on my Mac, but your tilt renderings seem to show the "interference" I had suggested. I would be interested to see how your model handles a rotation error that's corrected using tilt.

FWIW, I don't think a "skew" tilt adjustment is necessarily detrimental. Consider the model where the central post isn't parallel or coincident with the primary mirror axis (truss shift or orthogonality issue with the spider mounting), or the more common warped focuser mounting board. Sometimes, a little "skew" is the quick fix...


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SACK
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Re: Another innovation from Howie Glatter? new [Re: Pinbout]
      #6044389 - 08/24/13 11:23 PM

Thanks for showing this Danny! Thank you Vic for the explanation!
So the stalk example seems to "swing" the mirror out of or in to the light cone and is still round.
The other example, screws perpendicular to mirror face plane, actually tilts, and is now oval. Is that a good way to term it?
I asked above about rotation mimicking tilt, but lets pretend I have a secondary holder with no "swing" adjustment built in and no tilt adjustment as well, as shown in Danny's examples, but just a tilt adjustment along the long axis of the secondary mirror for the optimal right angle. Could rotation and spider vane adjustment, I guess up and down movement as viewed through your focuser or relative to that view, do the same thing as "tilt" error correction as I explained it?

Anyone, Vic,


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