Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

The long-awaited conversion to CN 3.0 is imminent. Please see this thread for important information.

Equipment Discussions >> Reflectors

Pages: 1 | 2 | 3 | 4 | (show all)
Vic Menard
Post Laureate
*****

Reged: 07/21/04

Loc: Bradenton, FL
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Vic Menard
Post Laureate
*****

Reged: 07/21/04

Loc: Bradenton, FL
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
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)


Post Extras: Print Post   Remind Me!   Notify Moderator  
auriga
Pooh-Bah


Reged: 03/02/06

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
Howie Glatter
Vendor


Reged: 07/04/06

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
choran
Carpal Tunnel
*****

Reged: 12/28/12

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?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Vic Menard
Post Laureate
*****

Reged: 07/21/04

Loc: Bradenton, FL
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!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Vic Menard
Post Laureate
*****

Reged: 07/21/04

Loc: Bradenton, FL
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".


Post Extras: Print Post   Remind Me!   Notify Moderator  
choran
Carpal Tunnel
*****

Reged: 12/28/12

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
choran
Carpal Tunnel
*****

Reged: 12/28/12

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
choran
Carpal Tunnel
*****

Reged: 12/28/12

Re: Another innovation from Howie Glatter? [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?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Another innovation from Howie Glatter? new [Re: Vic Menard]
      #6037430 - 08/20/13 10:50 PM Attachment (19 downloads)

here's two different holders.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Vic Menard
Post Laureate
*****

Reged: 07/21/04

Loc: Bradenton, FL
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...


Post Extras: Print Post   Remind Me!   Notify Moderator  
SACK
member
*****

Reged: 08/11/11

Loc: TX
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,


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | (show all)


Extra information
15 registered and 24 anonymous users are browsing this forum.

Moderator:  ausastronomer, Knuklhdastrnmr, Phillip Creed, JayinUT 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 3263

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics