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Another innovation from Howie Glatter?

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#1 auriga

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Posted 17 June 2013 - 11:04 PM

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

#2 Howie Glatter

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Posted 18 June 2013 - 08:54 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.

#3 csrlice12

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Posted 18 June 2013 - 09:09 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...

#4 Starman1

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Posted 18 June 2013 - 09:59 AM

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:

Attached Files



#5 Howie Glatter

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Posted 18 June 2013 - 11:01 AM

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.

#6 dscarpa

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Posted 18 June 2013 - 11:05 AM

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

#7 howard929

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Posted 18 June 2013 - 11:31 AM

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.

#8 turtle86

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Posted 18 June 2013 - 12:24 PM

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.

#9 acochran

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Posted 18 June 2013 - 04:49 PM

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

#10 jpcannavo

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Posted 18 June 2013 - 05:44 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

#11 BlackBirdCD

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Posted 18 June 2013 - 06:33 PM

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! :bow:

#12 careysub

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Posted 18 June 2013 - 08:58 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.


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.

#13 davidpitre

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Posted 18 June 2013 - 10:34 PM


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.

#14 csrlice12

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Posted 18 June 2013 - 10:35 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....

#15 azure1961p

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Posted 18 June 2013 - 10:50 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

#16 FirstSight

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Posted 19 June 2013 - 12:08 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.

#17 Jon Isaacs

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Posted 19 June 2013 - 04:28 AM

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

#18 Starman1

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Posted 19 June 2013 - 10:28 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.

#19 Jon Isaacs

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Posted 19 June 2013 - 10:44 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.


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

#20 davidmcgo

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Posted 19 June 2013 - 11:29 AM

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

Dave

#21 Jon Isaacs

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Posted 19 June 2013 - 11:52 AM

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

#22 mtb54703

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Posted 19 June 2013 - 12:58 PM

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.

#23 Starman1

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Posted 19 June 2013 - 01:20 PM

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.

#24 Vic Menard

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Posted 19 June 2013 - 01:38 PM

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.

#25 Vic Menard

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Posted 19 June 2013 - 01:49 PM

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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