Jump to content


Photo

Another innovation from Howie Glatter?

  • Please log in to reply
77 replies to this topic

#51 michael

michael

    Vendor (Starstructure Telescopes)

  • -----
  • Vendors
  • Posts: 842
  • Joined: 24 Jan 2004
  • Loc: Trinity Florida

Posted 21 June 2013 - 07:52 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

#52 choran

choran

    Vanguard

  • *****
  • Posts: 2151
  • Joined: 28 Dec 2012

Posted 18 August 2013 - 01:22 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.

#53 csrlice12

csrlice12

    Voyager 1

  • *****
  • Posts: 10824
  • Joined: 22 May 2012
  • Loc: Denver, CO

Posted 18 August 2013 - 01:58 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.....

#54 Cotts

Cotts

    Just Wondering

  • *****
  • Posts: 4826
  • Joined: 10 Oct 2005
  • Loc: Toronto, Ontario

Posted 18 August 2013 - 05:12 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

#55 CounterWeight

CounterWeight

    Cosmos

  • *****
  • Posts: 8160
  • Joined: 05 Oct 2008
  • Loc: Palo alto, CA.

Posted 18 August 2013 - 05:35 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.

#56 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 22874
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 18 August 2013 - 05:38 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

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.

#57 SACK

SACK

    Explorer 1

  • *****
  • Posts: 85
  • Joined: 11 Aug 2011
  • Loc: TX

Posted 18 August 2013 - 06:13 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. :grin: 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?

#58 Vic Menard

Vic Menard

    Aurora

  • *****
  • Posts: 4780
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted 18 August 2013 - 07:30 PM

...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.

#59 Pinbout

Pinbout

    Cosmos

  • *****
  • Posts: 7785
  • Joined: 22 Feb 2010
  • Loc: nj

Posted 18 August 2013 - 07:45 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.

#60 Peter Natscher

Peter Natscher

    Viking 1

  • -----
  • Posts: 777
  • Joined: 28 Mar 2006
  • Loc: Central Coast California

Posted 18 August 2013 - 07:57 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.

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



#61 Vic Menard

Vic Menard

    Aurora

  • *****
  • Posts: 4780
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted 18 August 2013 - 08:01 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.

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.

#62 Pinbout

Pinbout

    Cosmos

  • *****
  • Posts: 7785
  • Joined: 22 Feb 2010
  • Loc: nj

Posted 18 August 2013 - 08:14 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.

#63 Vic Menard

Vic Menard

    Aurora

  • *****
  • Posts: 4780
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted 18 August 2013 - 08:33 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.

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.

#64 Jeff Morgan

Jeff Morgan

    Fly Me to the Moon

  • *****
  • Posts: 5688
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 18 August 2013 - 09:56 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.



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.

#65 Pinbout

Pinbout

    Cosmos

  • *****
  • Posts: 7785
  • Joined: 22 Feb 2010
  • Loc: nj

Posted 18 August 2013 - 10:01 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

#66 auriga

auriga

    Apollo

  • -----
  • Posts: 1343
  • Joined: 02 Mar 2006

Posted 19 August 2013 - 11:00 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-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

#67 Howie Glatter

Howie Glatter

    Vendor

  • -----
  • Vendors
  • Posts: 867
  • Joined: 04 Jul 2006

Posted 20 August 2013 - 05:50 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

#68 choran

choran

    Vanguard

  • *****
  • Posts: 2151
  • Joined: 28 Dec 2012

Posted 20 August 2013 - 02:04 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?

#69 Vic Menard

Vic Menard

    Aurora

  • *****
  • Posts: 4780
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted 20 August 2013 - 03:03 PM

...What am I missing?

Clarification (on my part). :foreheadslap:

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! :p

#70 Vic Menard

Vic Menard

    Aurora

  • *****
  • Posts: 4780
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted 20 August 2013 - 03:12 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".

#71 choran

choran

    Vanguard

  • *****
  • Posts: 2151
  • Joined: 28 Dec 2012

Posted 20 August 2013 - 03:33 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.

#72 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 22874
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 20 August 2013 - 03:37 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".

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.

#73 choran

choran

    Vanguard

  • *****
  • Posts: 2151
  • Joined: 28 Dec 2012

Posted 20 August 2013 - 04:15 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.

#74 choran

choran

    Vanguard

  • *****
  • Posts: 2151
  • Joined: 28 Dec 2012

Posted 20 August 2013 - 04:17 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?

#75 Pinbout

Pinbout

    Cosmos

  • *****
  • Posts: 7785
  • Joined: 22 Feb 2010
  • Loc: nj

Posted 20 August 2013 - 09:50 PM

here's two different holders.

Attached Files








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics