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Equipment Discussions >> Classic Telescopes

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starman876
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How old is it
      #5665943 - 02/06/13 08:06 PM Attachment (54 downloads)

Have had this a few years thought I would restore it

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starman876
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Re: How old is it new [Re: starman876]
      #5665947 - 02/06/13 08:12 PM Attachment (46 downloads)

pic of primary. stange way to hold it in place, There are holes in the side of the mirror and the clips have pins in them.

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starman876
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Re: How old is it new [Re: starman876]
      #5665950 - 02/06/13 08:13 PM Attachment (30 downloads)

pic of secondary. Little guy about an inch in diameter

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terraclarke
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Re: How old is it new [Re: starman876]
      #5666078 - 02/06/13 09:44 PM

I presume it's a true Cassegrain, (no corrector plate)? I'm guessing 1940s?

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starman876
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Re: How old is it new [Re: terraclarke]
      #5666100 - 02/06/13 09:55 PM Attachment (33 downloads)

pic of the front

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terraclarke
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Re: How old is it new [Re: starman876]
      #5666102 - 02/06/13 09:56 PM

The focuser looks like a late 50s Jaegers.

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starman876
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Re: How old is it new [Re: terraclarke]
      #5666112 - 02/06/13 10:01 PM

That is what I thought. Not sure if it original. I am trying to figure out is the way the mirror is mounted is indictave of a certain time. I have not clue when the clips with pins was only way. Every mirror clip I have seen clamps on the front edge of the mirror. This mirror has holes in it for the pins on the clips.

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starman876
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Re: How old is it new [Re: starman876]
      #5666201 - 02/06/13 10:55 PM Attachment (31 downloads)

One more view

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Grava T
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Reged: 06/18/08

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Re: How old is it new [Re: starman876]
      #5666573 - 02/07/13 07:25 AM

The holes in the mirror clips could be there to place dollops of silicon to hold the mirror in place. Are they threaded?

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starman876
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Re: How old is it new [Re: Grava T]
      #5666587 - 02/07/13 07:45 AM

the clips have pins in them that go into the holes in the side of the mirror to hold it in place.

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DAVIDG
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Re: How old is it new [Re: starman876]
      #5666607 - 02/07/13 08:09 AM

The focuser is from the 1960's and is Jaegers. The mirror cell and spider are possibly a Novak again from the 1960's. The optical design is most likely a Dall Kirkham. 3-B Optical and Coulter Optics sold mirror sets. You'll need to add at least a primary mirror baffle tube or the image will be washed out with sky flooding. Also the distance from the primary to the secondary is critical. You need to measure that exact focal length of the primary and determine if it an ellipse or a parabola. From those numbers it can be calculated what the spacing should be. My guess is that it f/20 system using a 6" f/5 primary.
The reason for the mirror cell design using pins to hold the primary was to not introduce diffraction from the mirror clips. Because the system is using a small diamater secondary and most likely between F/15 and F/20 someone was try to make a high res planetary scope but without the baffles the image contrast will be poor.

- Dave


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starman876
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Re: How old is it new [Re: DAVIDG]
      #5666633 - 02/07/13 08:33 AM

When I reflected the light off the mirror it focused at 40 inches. Making the mirror around F6. Dpepending on the secondary magnification that could make it F20 or more. Wondering if this is a English design with the small secondary.

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starman876
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Re: How old is it new [Re: starman876]
      #5666642 - 02/07/13 08:42 AM

Also, I have a Coulter cassegrain from that time frame and it looks nothing like this mirror. This is much older. I still ask " who has seen a mirror mounted like this before"

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DAVIDG
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Re: How old is it new [Re: starman876]
      #5666764 - 02/07/13 10:13 AM

I've seen amateurs use pins and also grooves along the edge to hold mirrors a number of times. The issues is that the holes need to be made in the glass before it is ground. If not because of the Tywman effect, the stress released during boring of the holes may distore the optical figure.
The primary looks to be made from a Corning Pyrex "slope sided" blank that were common from the '50's into the mid 1970's. Both Coulter and 3B used them, depending on when the optics were made and they were also what was sold in mirror making kits by Edmund and Jaegers. They were most common in the 1960's.
A number of ATM constructed Cassegrains were built following Novak's book on the subject "Cassegrain Notes" http://bobmay.astronomy.net/CassNotes/index.htm using commerical optics and Novak parts.

- Dave


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