Javascript Disabled Detected

You currently have javascript disabled. Several functions may not work. Please re-enable javascript to access full functionality.

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

? MYSTERY ? EDMUNDS ? 6" CASSEGRAIN ?

Started by TOM KIEHL , Jun 25 2013 03:10 PM

«
Prev

Next

This topic has been archived. This means that you cannot reply to this topic.

129 replies to this topic

#101 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:23 PM

4

Attached Thumbnails

Back to top

#102 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:25 PM

5

Attached Thumbnails

Back to top

#103 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:25 PM

6

Attached Thumbnails

Back to top

#104 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:26 PM

7

Attached Thumbnails

Back to top

#105 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:27 PM

8

Attached Thumbnails

Back to top

#106 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:28 PM

9

Attached Thumbnails

Back to top

#107 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:28 PM

10

Attached Thumbnails

Back to top

#108 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:29 PM

11

Attached Thumbnails

Back to top

#109 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:29 PM

12

Attached Thumbnails

Back to top

#110 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:30 PM

13

Attached Thumbnails

Back to top

#111 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:31 PM

14

Attached Thumbnails

Back to top

#112 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:32 PM

15

Attached Thumbnails

Back to top

#113 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:32 PM

16

Attached Thumbnails

Back to top

#114 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 12:37 PM

17

THAT'S ALL FOLKS,,,,STICK A FORK IN IT,,,,,IT'S A WRAP,,,THE END,,,,THAT'S ALL SHE WROTE,,,IT'S FINALLY FINISHED......

THANKS TO EVERYONE FOR THE HELP :bow:

Attached Thumbnails

Back to top

#115 DAVIDG

Voyager 1

Posts: 12,481
Joined: 02 Dec 2004

Posted 23 June 2014 - 12:56 PM

Tom,
Looks great. So what do the images look like ? I haven't finished my DK. Got busy restoring the local high schools 10" Cave Cass. mount and dome.

- Dave

Back to top

#116 TOM KIEHL

Fly Me to the Moon

topic starter

Posts: 5,372
Joined: 17 Nov 2012

Posted 23 June 2014 - 01:21 PM

Tom,
Looks great. So what do the images look like ? I haven't finished my DK. Got busy restoring the local high schools 10" Cave Cass. mount and dome.

- Dave

Before I did the paint and finish... This winter I had it out for star test and star collimation Dave those test proved to be very good ..tooo cold to mess around too long outside. Think I did swing around and check out JUP real quick It looked good too. then back in the house. I took all the optics out to do the paint and finish ,reassembled and did a bench collimation last week. have to get it out to test and star collimate again soon I hope .then I'll have better weather conditions to play around,, then in the dead of winter

Back to top

#117 Terra Nova

ISS

Posts: 30,787
Joined: 29 May 2012

Posted 23 June 2014 - 02:00 PM

That is very nice Tom. It has the exact same finder as on my 4" F15 Edmund refractor.

Back to top

#118 Terra Nova

ISS

Posts: 30,787
Joined: 29 May 2012

Posted 23 June 2014 - 02:03 PM

I cannot for the life of me understand why noone (or darned few anyway) makes a classical Cassegrain like that anymore.

Back to top

#119 jrcrilly

Refractor wienie no more

Posts: 36,025
Joined: 30 Apr 2003

Posted 23 June 2014 - 02:16 PM

I cannot for the life of me understand why noone (or darned few anyway) makes a classical Cassegrain like that anymore.

It's awfully long (slow) for a classical Cass. I'd think it more likely to be a D-K. The reason we don't see very many classical Cassegrains is that very nearly the same performance can be had by relaxing the mirror curves to a slower D-K, making a more affordable instrument. Or the primary can be pushed into a hyperboloid at a modest increase in cost and similar performance can be had in a much faster package. Both alternatives are much more popular than the original, which offers the least bang of the three for the buck.

Back to top

#120 Bomber Bob

ISS

Posts: 23,504
Joined: 09 Jul 2013

Posted 23 June 2014 - 02:58 PM

A great restoration thread! Lots of inspiration as I get ready to work on my Edmund 4.25" mount. Thanks for the detailed photos and descriptions. Your Cass is a beauty! F20... 200x with an OR12.5 - excellent!

Back to top

#121 DAVIDG

Voyager 1

Posts: 12,481
Joined: 02 Dec 2004

Posted 23 June 2014 - 03:31 PM

The reason why you don't see classic Cassegrains is the difficulty in making the convex hyberbolic secondary. To do it right you need a Hindle sphere which is a concave spherical mirror that has the radius of curvature equal to the focal length of the primary used in the cassegrain telescope. So if your making a cass with F/4 primary you need to make a hindle sphere that is around F/2. On top of that, polishing a small convex hyberbola is not easy, especially getting the edge correct which is the most critical part. Here is a link to a my good friends Dick Parker's setup http://mirrorworksho...phereBench.html
Dall Kirkhams are easier to make so more popular. Since the primary is an ellipse is has less correction then a parabola and the same test techniques can be used to make it as one uses to make a parabola. The secondary mirror is a convex sphere. Since a sphere has no optical axis you can grind a larger disk that is easy to handle then cut out the ssmaller secondary from it. When it comes to testing, the concave "tool" used to grind the convex secondary can be polished, figured and tested just like making any other sphere then used as a test plate to check the figure of the convex secondary by contact interference. So the testing the secondary is much easier as well. If your making a number of optical sets you can grind and figure a large enough disk to cut out the needed number of secondaries from just the one disk.
What you lose in a Dall Kirkham is off axis performance. It has much more coma then a classic Cass so the useable field of view is much smaller.

- Dave

Back to top

#122 jrcrilly

Refractor wienie no more

Posts: 36,025
Joined: 30 Apr 2003

Posted 23 June 2014 - 07:52 PM

The reason why you don't see classic Cassegrains is the difficulty in making the convex hyberbolic secondary.

Don't think so. Other designs (RC, ACF, others) use hyperboloid secondaries and are still are much more common then the classical Cass. Even the RC, with not one but two hyperboloid mirrors is far more common. The CC is at the worst point in the performance/difficulty-to-produce curve. I liked mine (a Takahashi) but it wasn't a good value.