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Equipment Discussions >> Classic Telescopes

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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
More mysteries ... new
      #6148575 - 10/20/13 03:18 PM Attachment (81 downloads)

Seems like a good classics weekend for all!

This year the theme for me has been mysteries - scopes, mounts, optics, eps - all sorts. Even an Nihon Seiko (posted earlier). I haven't caught up on most of them ... so here are a few more, for your consideration.

This one is a real oddball a 7 3/4" x 26" Cassegrain OTA, that looks like a kit build. I put it on an Edmund/Anchor/Jaegers 1" GEM to star test it - astigmatic - probably a pinched mirror/corrector.


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: wfj]
      #6148603 - 10/20/13 03:34 PM Attachment (52 downloads)

Speaking of the corrector, look at the size of the aluminized spot on the corrector (clear aperture 5.5", spot 2.37").

Yet the corrector is a thin flat plate, not a thick meniscus.

It's a mystery to me how this even can optically work, as it looks like an optical window with an aluminized spot.

The primary mirror is larger in diameter, fills the tube ID so I'd estimate 6.5".

It could be a very weak negative lens like a Schmidt corrector, but still the spot is hard to figure. The primary seems to have a ROC of 96" or so thus f/8?

Could this be a coaxial folded "newt"? If so I've never seen such, much less a kit for same.


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: wfj]
      #6148609 - 10/20/13 03:38 PM Attachment (39 downloads)

The back story on this is said to be a retired Lockheed machinist who worked on satellites. The focuser does seem to bear that out ...

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davidmcgo
Pooh-Bah
*****

Reged: 10/09/04

Loc: San Diego, CA
Re: More mysteries ... new [Re: wfj]
      #6148756 - 10/20/13 05:36 PM

Any relay lenses in the baffle tube?

Dave


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terraclarke
Post Laureate
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Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: More mysteries ... new [Re: davidmcgo]
      #6148910 - 10/20/13 06:59 PM

Neat scope!

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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: davidmcgo]
      #6149009 - 10/20/13 07:50 PM

Quote:

Any relay lenses in the baffle tube?

Dave



Nope. Nor a baffle tube - I made one out of a core of paper towels

No lens glued to corrector either.


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... [Re: terraclarke]
      #6149018 - 10/20/13 07:54 PM

Quote:

Neat scope!



Yeah - it was fairly competently executed. It looks like a kit build, but I thought I'd see all of the Dall Kirkham kits from Coulter and others, and the few Tinsley "classical cass" kits. And the german SCT kits too.

Still trying to figure out how to remove the corrector ...


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: wfj]
      #6149126 - 10/20/13 09:30 PM Attachment (31 downloads)

... and here's the eyepieces that came with it ... one on right has no marks, other has a 1" .

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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: wfj]
      #6149131 - 10/20/13 09:31 PM Attachment (19 downloads)

... field lens side ...

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terraclarke
Post Laureate
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Reged: 05/29/12

Loc: Just South of the Mason-Dixon ...
Re: More mysteries ... new [Re: wfj]
      #6149347 - 10/21/13 07:15 AM

The 1 inch looks like a Huygens. I bet the other is a 1/2 inch Ramsden.

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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: terraclarke]
      #6149981 - 10/21/13 02:30 PM Attachment (27 downloads)

Terra,
You are exactly, perfectly correct in both cases. Clearly no mystery for you. A gold star!

Here's a harder one - the unmounted finder. The eerie thing about this piece, is that I swear I used one identical to it on a 12" Dynascope in the early 70's:


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: wfj]
      #6149992 - 10/21/13 02:36 PM Attachment (22 downloads)

It's a 50mm finder with a 10mm exit pupil (5x) and a FOV about the size of the great square of Pegasus. The thumb screw allows you to separately adjust the reticule focus plane.

The other end has a tank eyepiece:


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DAVIDG
Post Laureate
*****

Reged: 12/02/04

Loc: Hockessin, De
Re: More mysteries ... new [Re: wfj]
      #6150138 - 10/21/13 04:06 PM

The finder is an old Edmund unit. I have one. It was made with a WWII "Erfle" eyepiece.
As for the optical design of the telescope, it is most likely either a folded Newtonian or a Maksutov. In a Mak the corrector can have shallow curves when it is used with a slow primary.

- Dave


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: DAVIDG]
      #6151815 - 10/22/13 02:41 PM Attachment (18 downloads)

Quote:

The finder is an old Edmund unit. I have one. It was made with a WWII "Erfle" eyepiece.



Oh yeah - "Edmund Giant Finder" in the catalog. Thanks, I knew I remembered it from the past, that nails it.
Quote:


As for the optical design of the telescope, it is most likely either a folded Newtonian or a Maksutov. In a Mak the corrector can have shallow curves when it is used with a slow primary.

- Dave



... which is why I'm taking it apart, which it looks like the corrector bezel is glued on, so the "corrector" cell slides out the mirror end.

By the way, the star test showed a stretched circle with perhaps a weaker single inner ring, with a sharp disruption of the outer ring, as if two back to back D's in mirror image of slightly differing size - never seen anything like it. Similar pattern inside focus. No center dot in pattern.

So I'm first "debugging" the optics, attempting to find the source of the diffraction pattern. I did notice on the moon a combination of issues - very sharp crater focus/resolution but only in certain positions, uneven focal plane, and fogging/glare. The last is due to baffling issues. I'm not yet certain about any SA yet, can't determine degree of correction. Could split sub microsecond fairly even magnitude doubles with a small Airy disk though.

So I need to find the culprit for the astigmatism and the feature. Strain on the mirror, crack, or a pinched corrector - what do you think it is?

Here's the primary in a machined brass cell on top of a particle board end cap - looks like a 6" dob repurposed item:


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: wfj]
      #6151820 - 10/22/13 02:45 PM Attachment (17 downloads)

Note - four top screws and four side screws above.

Is the mirror under tension, possibly bound as if pressure inserted like a bushing into a casting?

The mirror is sealed in - view from below:


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DAVIDG
Post Laureate
*****

Reged: 12/02/04

Loc: Hockessin, De
Re: More mysteries ... new [Re: wfj]
      #6151864 - 10/22/13 03:14 PM

Since you have the mirror out of the OTA, I would bench test it. In a few minutes you'll know if it's something close to a parabola or spherical. If spherical then the front glass would need to be a menicus for the system to have a chance of working. If it looks like the mirror is parabolic then the front glass needs to be a high quality optical window. You also know if the usual diffraction pattern is coming from the mirror or the corrector. If it coming from the mirror then you can take it out the cell and see if it goes away.
I've seen a couple of homemade "telescopes" made from military optical parts that don't belong together and just won't work. This has that look about it. My guess is that the mirror might be Ok but the window/corrector is not a precision piece of optics.

- Dave


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Darren Drake
Carpal Tunnel
*****

Reged: 10/09/02

Loc: Chicagoland
Re: More mysteries ... new [Re: DAVIDG]
      #6152271 - 10/22/13 07:10 PM

The back of this scope looks exactly like my Meade 8 inch Starfinder I used to own. I even drilled the 3 holes exactly like the ones shown here. Interesting.

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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: More mysteries ... new [Re: Darren Drake]
      #6152980 - 10/23/13 05:11 AM

Quote:

The back of this scope looks exactly like my Meade 8 inch Starfinder I used to own. I even drilled the 3 holes exactly like the ones shown here. Interesting.




Interesting.. With the particle board and sonotube construction, it definitely screams 1980's construction techniques.

Jon


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: DAVIDG]
      #6154405 - 10/23/13 08:49 PM Attachment (14 downloads)

Quote:

Since you have the mirror out of the OTA, I would bench test it. In a few minutes you'll know if it's something close to a parabola or spherical.




Took me a while to find a flashlight to convert to tester:

3-line ronchi at 96" : significant convex - parabola not sphere.

Quote:

If spherical then the front glass would need to be a menicus for the system to have a chance of working. If it looks like the mirror is parabolic then the front glass needs to be a high quality optical window.




Working on getting out the "corrector" so I can test it separately.
Quote:

You also know if the usual diffraction pattern is coming from the mirror or the corrector. If it coming from the mirror then you can take it out the cell and see if it goes away.





Still have it in the cell, and the lines look more "bent" near the edge, as if its a "turned edge". Could you get such from a 1" thick slab somehow warped under tension/compression ?

Quote:


I've seen a couple of homemade "telescopes" made from military optical parts that don't belong together and just won't work. This has that look about it.





It does at that.

Quote:

My guess is that the mirror might be Ok but the window/corrector is not a precision piece of optics.


- Dave



Like a piece of window glass that he had aluminized a spot on.

Here's another part of the mystery - another pair of similar optics:


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: More mysteries ... new [Re: Darren Drake]
      #6154420 - 10/23/13 09:01 PM

Quote:

The back of this scope looks exactly like my Meade 8 inch Starfinder I used to own. I even drilled the 3 holes exactly like the ones shown here. Interesting.




Thanks for that - never had one of those. Did have a similar Orion DS-12 inch with a particle board, glued on mirror (three enormous blobs of RTV), but it had wingnuts out the rear of the cell.

So its likely a Starfinder cell/tube - did it have the same front bezel?


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