Jump to content

  •  

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.

Photo

Miscellany

  • Please log in to reply
764 replies to this topic

#751 clamchip

clamchip

    Voyager 1

  • *****
  • topic starter
  • Posts: 10,191
  • Joined: 09 Aug 2008
  • Loc: Seattle

Posted 20 February 2020 - 01:01 PM

I found this picture in my files.

No nothing on it about it.

Isn't it just a dream.

Robert

 

873e165a89956b23f5a0ce1b1b7bcd79.jpg

 


  • tim53, Terra Nova, PawPaw and 5 others like this

#752 TSSClay

TSSClay

    Viking 1

  • *****
  • Posts: 559
  • Joined: 22 Oct 2013
  • Loc: Manchester MI

Posted 21 February 2020 - 02:05 PM

Robert,

 

A good friend of mine has that same setup.  I think it is a nice idea but he has found it is hard to travel with.  He uses it as his "winter observatory" parked in a daughter's back yard out in the country.  To travel he has an enclosed trailer with a complete astrophoto setup.  He sleeps in the trailer after he sets up his rig.

 

Clay


  • clamchip and Stevegeo like this

#753 clamchip

clamchip

    Voyager 1

  • *****
  • topic starter
  • Posts: 10,191
  • Joined: 09 Aug 2008
  • Loc: Seattle

Posted 23 February 2020 - 02:05 PM

I feel like working on my Cassegrain again.

This telescope was built in the Yerkes observatory workshops in the 1960's.

Mr. Grenfell graduated before he finished the telescope.

Dr. Grenfell retired Research Professor University of Washington.

I found he was selling his telescope on craigs list of all places.

I have not been able to get the scope to focus and I just assumed it is a

classical cass but now I'm wondering if it's a Dall-Kirkham.

The Dall-Kirkham is much easier to make, a more logical choice for the

amateur telescope maker.

All I need to do is figure out a way to check the figure on the primary!

If it's a ellipse than it's a DK and the unfinished? secondary only needs

to be a sphere.

Robert 

 

post-50896-0-49580000-1543360191_thumb.jpg

post-50896-0-46767900-1543440693_thumb.jpg


  • tim53, KentTolley, Terra Nova and 3 others like this

#754 Terra Nova

Terra Nova

    ISS

  • *****
  • Posts: 21,253
  • Joined: 29 May 2012
  • Loc: Middle Earth

Posted 23 February 2020 - 02:23 PM

Time to dust off and fire up the old Foucault tester!


  • clamchip likes this

#755 clamchip

clamchip

    Voyager 1

  • *****
  • topic starter
  • Posts: 10,191
  • Joined: 09 Aug 2008
  • Loc: Seattle

Posted 23 February 2020 - 02:50 PM

Yes, the Foucault would probably be the best way.

I did find this I might try:

http://www.atm-works...onchi-test.html

The primary is finished and coated so I just need to determine if its a

parabolic or elliptical surface to know if I have a classical or DK.

I forgot I also added a Newtonian focus (reversible, I used existing holes) I don't

remember the results of this, it would also tell me the design. The DK cannot be

used as a Newtonian.

Robert

 

post-50896-0-03447700-1543531712_thumb.jpg

post-50896-0-26696600-1543531627_thumb.jpg


Edited by clamchip, 23 February 2020 - 02:56 PM.

  • Terra Nova, PawPaw, Bomber Bob and 2 others like this

#756 clamchip

clamchip

    Voyager 1

  • *****
  • topic starter
  • Posts: 10,191
  • Joined: 09 Aug 2008
  • Loc: Seattle

Posted 23 February 2020 - 07:17 PM

I did some visual tests at Newtonian focus and I'm pretty sure the primary is parabolic.

I don't think I would have a sharp high power view if anything less than parabolic at f/5.375

meaning this telescope is more than likely a classical cass.

Although a elliptical figure (DK) falls right in between a sphere and a Parabolic.

So I think that the secondary will need to have a Hyperbolic figure.

It's all coming back to me now, this is where I left off on this scope a year or two ago.

I'm going to buy some new shirts with breast pockets so I can have a note pad with me at

all times. I've got so start writing this stuff down. I spent the entire day on this needlessly.

 

Robert


Edited by clamchip, 23 February 2020 - 07:18 PM.

  • Bomber Bob and AstroKerr like this

#757 clamchip

clamchip

    Voyager 1

  • *****
  • topic starter
  • Posts: 10,191
  • Joined: 09 Aug 2008
  • Loc: Seattle

Posted 24 February 2020 - 08:58 PM

Here's a good article describing the various Cassegrain designs:

http://www.rfroyce.com/cassegrains.htm

 

Robert


  • tim53 and AstroKerr like this

#758 DAVIDG

DAVIDG

    Cosmos

  • *****
  • Posts: 9,245
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 25 February 2020 - 11:48 AM

 Robert,

     You should confirm that the primary is parabolic and also how well it is figured. If  you have it setup as a Newtonian then place you optical flat in front of the scope and do a double pass test. If it is a parabola you should see straight bands . If it an ellipse the band will bow. I would caution about assuming  it is a parabola based on how well the images looks. Like I have said many times amateurs don't realize how "good" a 1/2 wave or worse image looks. It is not a fuzzy mess that won't come to focus. 

 

                     - Dave



#759 clamchip

clamchip

    Voyager 1

  • *****
  • topic starter
  • Posts: 10,191
  • Joined: 09 Aug 2008
  • Loc: Seattle

Posted 25 February 2020 - 12:25 PM

My largest flat is 6 inch.

I could try a oil pan flat.

I also need to stiffen up the secondary support, at high power it

vibrates and will not settle down.

I'm going to replace the wires with bicycle spokes since the wires

are already screwed into bicycle spoke nipples.

Robert

 

post-50896-0-03447700-1543531712_thumb.jpg


Edited by clamchip, 25 February 2020 - 12:27 PM.


#760 DAVIDG

DAVIDG

    Cosmos

  • *****
  • Posts: 9,245
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 25 February 2020 - 01:50 PM

 Your 6" flat will work.  Test in the newtonian configuration and you just need to place the flat so it is first in the center of the mirror and then off  to the side so you can test the edge.  Also since the primary is coated you can test the telescope in Cassegrain configuration even with the secondary uncoated. Again just place the optical flat  so it centered up in the primary.  Since the spacing of the Cassegran secondary changes the overall correction of the system  you  can slowing change it's position and see if you can find a position were the correction is the best. Note that when you move the secondary by a small amount it is going to change the back focus and a much large amount so your going to have to focus the Ronchi grating each time.  If the system always tests with a large amount of spherical aberration then the secondary most likely hasn't been figured. 

 

                      - Dave 



#761 clamchip

clamchip

    Voyager 1

  • *****
  • topic starter
  • Posts: 10,191
  • Joined: 09 Aug 2008
  • Loc: Seattle

Posted 25 February 2020 - 02:45 PM

Thanks Dave, I'll try it with my 6 inch flat.

 

Robert



#762 Stevegeo

Stevegeo

    Messenger

  • *****
  • Posts: 468
  • Joined: 29 Jan 2019
  • Loc: Otisco ny.

Posted 25 February 2020 - 06:37 PM

My largest flat is 6 inch.

I could try a oil pan flat.

I also need to stiffen up the secondary support, at high power it

vibrates and will not settle down.

I'm going to replace the wires with bicycle spokes since the wires

are already screwed into bicycle spoke nipples.

Robert

 

attachicon.gifpost-50896-0-03447700-1543531712_thumb.jpg

I will add a suggestion  to the bicycle spoke... use BMX spokes, the HEAVIEST,   with the heavy duty spoke nipples .. make them tite, view something, then tighten a bit more.

I saw a thread somewhere somebody was using bicycle rims in a ATM scope.  Interesting idea that is only lightweight, but extremely strong.

Stevegeo,Area3751  Otisco  Lake,  NY


  • clamchip likes this

#763 Steve Allison

Steve Allison

    Apollo

  • *****
  • Posts: 1,247
  • Joined: 25 Nov 2016
  • Loc: Olympia, Wash. 98502

Posted 25 February 2020 - 11:56 PM

After reading the above linked article about Ronchi testing, I was delighted to learn that my cheap achromats do not exhibit spherical aberrations but rather are paraboloids! smile.gif


Edited by Steve Allison, 25 February 2020 - 11:57 PM.


#764 Terra Nova

Terra Nova

    ISS

  • *****
  • Posts: 21,253
  • Joined: 29 May 2012
  • Loc: Middle Earth

Posted 26 February 2020 - 07:21 AM

I found this article while researching another matter. Since many of us here are interested in the restoration of optical glass in old telescopes, eyepieces, binoculars, cameras, and other arcane optical elements and devices, I thought it might prove both interesting and perhaps even useful. Submitted for your own innate curiosity:

 

https://www.nature.c...1529-018-0037-2


  • clamchip and Bomber Bob like this

#765 Senex Bibax

Senex Bibax

    Mariner 2

  • -----
  • Posts: 297
  • Joined: 01 Feb 2019
  • Loc: Ottawa, ON

Posted 26 February 2020 - 07:33 AM

If you need unusually short spokes, I have a whole pile from Moulton 16" rims...

 

I will add a suggestion  to the bicycle spoke... use BMX spokes, the HEAVIEST,   with the heavy duty spoke nipples .. make them tite, view something, then tighten a bit more.

I saw a thread somewhere somebody was using bicycle rims in a ATM scope.  Interesting idea that is only lightweight, but extremely strong.

Stevegeo,Area3751  Otisco  Lake,  NY


  • clamchip likes this


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.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics