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Equipment Discussions >> Classic Telescopes

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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: DAVIDG]
      #5950414 - 07/01/13 09:48 PM

Dave, I notice that your mirror retaining tabs are thicker and wider than mine. Is that a thicker and wider "BACKING TAB" for a thinner sheetmetal tab that goes on first to hold the mirror in place? I don't have that backing piece, will have to fab. 3 of them, good idea, glad i seen the inside of your cell.

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DAVIDG
Post Laureate
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Reged: 12/02/04

Loc: Hockessin, De
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #5951175 - 07/02/13 11:29 AM Attachment (11 downloads)

Hi Tom,
Here is a close up of a backing tab. It's about 3/16" thick and like you said goes over the thinner tabs and they prevent the mirror from moving sideways.
You need to know the radius of curvature of the primary and secondary. With those pieces of information you can calculate the size and length of the baffles needed and also the spacing between the primary and secondary. Is there any writing on the mirrors that might indicate those measurments ?
If you have done mirror testing then the best way is with a Foucault tester and measure the primary mirror. Lacking that, then just using the primary mirror, project the image of the Moon onto a piece of the paper. For the secondary your going to need a spherometer. Since the secondary amplifies the focal length of the primary, a small change in it's position makes a big change in were the image comes to focus behind the primary. It also effects the optical correction of the system.

- Dave


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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: DAVIDG]
      #5951192 - 07/02/13 11:42 AM

Thanks Dave , Great picture, as far as the mirror's go , all I have is what you see,, and I don't have access to that kind of testing equipment. I will probably start with the figures that you worked up for me, and work with it from there.

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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #5951439 - 07/02/13 02:30 PM

Tom,
For me to calculate the baffling and spacing I'll need the radii on both the primary and secondary. You can tape a card to the end of yard stick and put the yard stick through the hole in the primary. Aim the assembly at the Moon and move the stick back and forth until the Moon is sharply focused on the card. Then read the distance from the card to the surface of the mirror. You should be able to get to within 1/8". I'm guessing that it will be very close to 24".
As for the secondary, if you can get the use of set of machinist calipers you can measure the thickness of the secondary at the very edge and also in the exact middle. That will tell us the sagitta or depth of the curve and from that we can calculate a good approximation to the radius. From there you can assemble the scope and have enough adjustments in the cells to find the exact spacings.
Without some data on the radii you can be adjusting things until the cows come home and never get a good image. I wonder if this happened to the original builder and why he gave up on the project ?

- Dave


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Dave M
Postmaster
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Reged: 08/03/04

Loc: Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: DAVIDG]
      #5951631 - 07/02/13 04:07 PM

Dave,
I have a Foucault tester Tom can use, dont have the caliper though. My tester is identical to the Stellafane tester, and iirc it has a 120 line ronchi screen in it.
So Tom, there ya go, come get it


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DAVIDG
Post Laureate
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Reged: 12/02/04

Loc: Hockessin, De
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: Dave M]
      #5951666 - 07/02/13 04:24 PM

Quote:

Dave,
I have a Foucault tester Tom can use, dont have the caliper though. My tester is identical to the Stellafane tester, and iirc it has a 120 line ronchi screen in it.
So Tom, there ya go, come get it




Dave,
That is great. Tom will also need to borrow the Ronchi grating from it once the optics are mounted in a tube so he can fine tune the position of the secondary using a star.
One can purchase a set of digital calipers from Habor Freight for under $15.
Dave, to answer your question about the gluing the baffle tube in place or not. I'm hoping that the fit will be snug enough once it is sealed with polyurethane and painted that I won't have to glue it in place.

- Dave


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Dave M
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Reged: 08/03/04

Loc: Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: DAVIDG]
      #5951756 - 07/02/13 05:06 PM

Dave, Thanks!, i was just curious

Tom, the top of your pool table would make a nice test bed.
You`l need to make a mirror stand, pretty simple, just a couple pieces of plywood and a couple 1" dowels.
http://tinyurl.com/qgr7a8z
I know your going to ask how to use the tester and
ronchi.
Go here
http://stellafane.org/tm/atm/test/tester-4.html
and see the section " How do i use the Ronchi Grating"


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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: Dave M]
      #5951841 - 07/02/13 06:18 PM

Sounds like a joint effort to me.

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Dave M
Postmaster
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Reged: 08/03/04

Loc: Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #5951878 - 07/02/13 06:36 PM

Now dont be scared its really fairly easy.

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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: Dave M]
      #5951884 - 07/02/13 06:41 PM

But MASTER , I am but a lowly Grasshopper

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Dave M
Postmaster
*****

Reged: 08/03/04

Loc: Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #5951915 - 07/02/13 07:08 PM

I can help you get the readings, then maybe we can get Dave to do the calculations..Dave`s the Master

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tim53
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Reged: 12/17/04

Loc: Highland Park, CA
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #5951925 - 07/02/13 07:15 PM

Quote:

But MASTER , I am but a lowly Grasshopper




Such knowledge is worth more than any fortune, Cookie!

-Tim.


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starman876
Postmaster
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Reged: 04/28/08

Loc: VA
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: tim53]
      #5951931 - 07/02/13 07:18 PM

Soon you too will be able to carry the hibachi grill with your forearms.

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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: starman876]
      #5972543 - 07/15/13 03:44 PM

Quote:

If I find everything for that 6" cassegrain I will post a pic. I bought it from the guy who made it in 1978. Looks like Toms, but it in a aluminum tube. Came with a 16X50 finder. No idea where that went.



Johann do you still have this? http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5665943/page...


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starman876
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Reged: 04/28/08

Loc: VA
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #5972550 - 07/15/13 03:47 PM

Yep, still do. However, that is not that cassegrain I was refering to.

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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: starman876]
      #5972569 - 07/15/13 03:56 PM

Did you ever post pictures of the other one? This one is close but not a "Twin" to mine...Would you please post pictures of the other one sometime?

Edited by TOM KIEHL (07/15/13 05:06 PM)


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starman876
Postmaster
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Reged: 04/28/08

Loc: VA
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #5972586 - 07/15/13 04:06 PM

OK when I find time

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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: starman876]
      #5972605 - 07/15/13 04:18 PM



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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #6098736 - 09/24/13 03:38 PM Attachment (5 downloads)

Movin' right along,,,, got the mount finished and that took some time to do. Had to strip and refinish all three legs. Three hand rubbed coats of Shellac and one final coat of Varnish, topped off with 0000 steelwool and Johnson's paste wax rub out to finish for a satin sheen. Buffed all new stainless nuts and bolts to a mirror finish. Made a toe saver. Painted the cast iron parts with satin black paint. Applied green felt to cradle for OTA. Now on to the Technical part of this restoration........THE OTA.
OH YES... and a special thanks to "Gelkin" for his kind help.
Now on with the show.....


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TOM KIEHL
Pooh-Bah
*****

Reged: 11/17/12

Loc: N.E. Ohio
Re: ? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ? new [Re: TOM KIEHL]
      #6098741 - 09/24/13 03:40 PM Attachment (4 downloads)

#2

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