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

Coulter 17.5 Primary advice.

This topic has been archived.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

#1 gkmurrell

gkmurrell

    Explorer 1

  • -----
  • topic starter
  • Posts: 92
  • Joined: 11 Jan 2016

Posted 11 January 2016 - 09:22 PM

So, I have a bunch of questions in regards to this mirror.  My father had one of the Odyssey II big red 17.5 scopes.   I looked through it a few times, but it was mostly his deal.  I know he had pulled the primary mirror out for cleaning because I helped him do it.  Unfortunately, last year my father passed away. Going through his shop,  I found the mirror  in a big Rubbermaid tuib wrapped in some sheepskins.  However, as I look around his shop and house, the rest of the telescope seems to be missing!  Now I am not super familiar with the scope, but I remember it was gigantic and red, so I have to assume I would be able to see it if it was around somewhere!  So this is where I start with the questions.  1st, would this mirror be worth the cost of building a scope around?  It seems to be in good shape with no blemishes or anything on it.  Would it be a super difficult or expensive undertaking?  I am a welder by trade, so I am pretty good at fabrication.  Would anyone have any suggestions on where I might start reading on how to go about building a scope?  I just have absolutely no idea how I would go about selecting a secondary mirror, or the dimensions that would be required etc.   I guess at this point I am just trying to figure out some way to put this to use, because I have to believe from the size and weight, that this mirror probably wasn't cheap!  Plus, I think being as it was my fathers, it would be kind of cool to build it if possible.  I know it was a hobby he really enjoyed.   Thank you in advance.



#2 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 11 January 2016 - 09:34 PM

Yes, the mirror would be worth it.

 

It wouldn't  cost much to build a scope around it. And much is a relative term.

Less than 1k.

 

Do you know if you have the oval flat mirror?

Where are you located.


Edited by Pinbout, 11 January 2016 - 09:34 PM.


#3 gkmurrell

gkmurrell

    Explorer 1

  • -----
  • topic starter
  • Posts: 92
  • Joined: 11 Jan 2016

Posted 11 January 2016 - 09:35 PM

I believe the mirror is 17.5 and appears to be round.  I am in Boise, Idaho. I haven't measured the thickness, but I would guess it to be between an 1 1/2 and 2 inches.


Edited by gkmurrell, 11 January 2016 - 09:36 PM.


#4 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 11 January 2016 - 09:42 PM

https://3dwarehouse....c2-21bbd903dea9

 

here's a model. I can get you layout drawings if ya want. if you know how to use a router and table saw its only the cost of material or I can get you connected with a friend who has a cnc.

 

I was asking about a small oval mirror, maybe he didn't keep it, you can get another one but that bumps the costs up, but no big deal.

 

the poles cost around $140

 

its probably around a sheet or two of $75 plywood.

 

you can make the cell.

 

if you have a drill press you can make the truss connectors for a fraction of the cost.

 

the focuser is another $165 to $275.


Edited by Pinbout, 11 January 2016 - 09:43 PM.


#5 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 11 January 2016 - 09:52 PM

the mirror box and cell would just scale up from this 12.5in

 

https://www.youtube....h?v=ifSMbmCxf1I

 

and the scope basically scaled up from this 10in

 

https://www.youtube....h?v=G3xu8CNBe0k


Edited by Pinbout, 11 January 2016 - 09:53 PM.


#6 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 11 January 2016 - 10:09 PM

or these plans could easily be scaled for your 17.5

 

https://3dwarehouse....8d444821f22cd11



#7 gkmurrell

gkmurrell

    Explorer 1

  • -----
  • topic starter
  • Posts: 92
  • Joined: 11 Jan 2016

Posted 11 January 2016 - 10:30 PM

If there is the smaller mirror, I haven't found it.  The big mirror is mounted on what looks to be either particle board or plywood.  There are three handles on the back of it.



#8 jallbery

jallbery

    Mercury-Atlas

  • *****
  • Posts: 2,554
  • Joined: 01 Nov 2015

Posted 11 January 2016 - 10:32 PM

The Coulter Odyssey II was a 17.5" F4.5 scope with a 4.25"x 6 5/16" secondary (at least according to http://umich.edu/~lo...jbrisbin.5.html)

 

The GSO 104mm secondary would be a close fit (about $165).



#9 prfesser

prfesser

    Mariner 2

  • *****
  • Posts: 294
  • Joined: 09 Sep 2013

Posted 11 January 2016 - 11:27 PM

So, I have a bunch of questions in regards to this mirror.  My father had one of the Odyssey II big red 17.5 scopes.   I looked through it a few times, but it was mostly his deal.  I know he had pulled the primary mirror out for cleaning because I helped him do it.  Unfortunately, last year my father passed away. Going through his shop,  I found the mirror  in a big Rubbermaid tuib wrapped in some sheepskins.  However, as I look around his shop and house, the rest of the telescope seems to be missing!  Now I am not super familiar with the scope, but I remember it was gigantic and red, so I have to assume I would be able to see it if it was around somewhere!  So this is where I start with the questions.  1st, would this mirror be worth the cost of building a scope around?  It seems to be in good shape with no blemishes or anything on it.  Would it be a super difficult or expensive undertaking?  I am a welder by trade, so I am pretty good at fabrication.  Would anyone have any suggestions on where I might start reading on how to go about building a scope?  I just have absolutely no idea how I would go about selecting a secondary mirror, or the dimensions that would be required etc.   I guess at this point I am just trying to figure out some way to put this to use, because I have to believe from the size and weight, that this mirror probably wasn't cheap!  Plus, I think being as it was my fathers, it would be kind of cool to build it if possible.  I know it was a hobby he really enjoyed.   Thank you in advance.

I would strongly suggest The Dobsonian Telescope by Kriege and Berry, from Willmann-Bell http://www.willbell.com.  Very complete and lots of photos.  Answers lots of "how" and "why" questions about building a Dobsonian.  Daughter got me a copy for christmas.

Best -- Terry



#10 KidOrion

KidOrion

    Vanguard

  • *****
  • Posts: 2,160
  • Joined: 07 Jul 2007

Posted 11 January 2016 - 11:46 PM

 

So, I have a bunch of questions in regards to this mirror.  My father had one of the Odyssey II big red 17.5 scopes.   I looked through it a few times, but it was mostly his deal.  I know he had pulled the primary mirror out for cleaning because I helped him do it.  Unfortunately, last year my father passed away. Going through his shop,  I found the mirror  in a big Rubbermaid tuib wrapped in some sheepskins.  However, as I look around his shop and house, the rest of the telescope seems to be missing!  Now I am not super familiar with the scope, but I remember it was gigantic and red, so I have to assume I would be able to see it if it was around somewhere!  So this is where I start with the questions.  1st, would this mirror be worth the cost of building a scope around?  It seems to be in good shape with no blemishes or anything on it.  Would it be a super difficult or expensive undertaking?  I am a welder by trade, so I am pretty good at fabrication.  Would anyone have any suggestions on where I might start reading on how to go about building a scope?  I just have absolutely no idea how I would go about selecting a secondary mirror, or the dimensions that would be required etc.   I guess at this point I am just trying to figure out some way to put this to use, because I have to believe from the size and weight, that this mirror probably wasn't cheap!  Plus, I think being as it was my fathers, it would be kind of cool to build it if possible.  I know it was a hobby he really enjoyed.   Thank you in advance.

I would strongly suggest The Dobsonian Telescope by Kriege and Berry, from Willmann-Bell http://www.willbell.com.  Very complete and lots of photos.  Answers lots of "how" and "why" questions about building a Dobsonian.  Daughter got me a copy for christmas.

Best -- Terry

 

Watch out for their formula for measuring the I.D. of the upper cage--it apparently produces a cage that's too small.



#11 opticsguy

opticsguy

    Surveyor 1

  • *****
  • Posts: 1,787
  • Joined: 02 Feb 2009

Posted 12 January 2016 - 12:09 AM

Take your time and explore and find all things left by your dad.  Enough searching and organizing should bring up the secondary mirror and focuser and other parts.  Possibly all packed away in a box.  No need to rush and spend a bunch of money on items you probably already have.



#12 gkmurrell

gkmurrell

    Explorer 1

  • -----
  • topic starter
  • Posts: 92
  • Joined: 11 Jan 2016

Posted 12 January 2016 - 12:11 AM

Thank you both for the information.  So I guess it is safe to assume from looking at the sketches/plans that have been posted here, that no one uses the Sona tube anymore?  I remember that being heavy as hell!



#13 gkmurrell

gkmurrell

    Explorer 1

  • -----
  • topic starter
  • Posts: 92
  • Joined: 11 Jan 2016

Posted 12 January 2016 - 12:27 AM

https://3dwarehouse....c2-21bbd903dea9

 

here's a model. I can get you layout drawings if ya want. if you know how to use a router and table saw its only the cost of material or I can get you connected with a friend who has a cnc.

 

I was asking about a small oval mirror, maybe he didn't keep it, you can get another one but that bumps the costs up, but no big deal.

 

the poles cost around $140

 

its probably around a sheet or two of $75 plywood.

 

you can make the cell.

 

if you have a drill press you can make the truss connectors for a fraction of the cost.

 

the focuser is another $165 to $275.

Yes, I can use a router table saw, etc.  That is one thing about dad, he had about two of everything for wordworking.  If you had layout stuff, that would be great.  I guess that I could tell better from the actual plans, but are any of these parts IE poles aluminum?  I have access to a plasma, pressbrake, and aluminum welders.  

 

Thank you so much for the information!



#14 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 12 January 2016 - 12:39 AM

The poles 1.25x.05 wall alum 6061 or 63 doesnt matter

I use 1018 steel for the frame of the cell. You need the weight in the back to help balance the scope, especially with the ultra lights.

 

The spider made from .02 1018 steel sheets. A sheer is good, brakes not necessary.

 

I'd stay away from gso 2ndry's if you afford it, but if you cant get it and upgrade later.



#15 gkmurrell

gkmurrell

    Explorer 1

  • -----
  • topic starter
  • Posts: 92
  • Joined: 11 Jan 2016

Posted 12 January 2016 - 12:44 AM

So what secondary would you recommend if not the gso?



#16 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 12 January 2016 - 12:46 AM

http://www.antaresop...m/SEMirrors.php

 

The 4in 1/12 wave


Edited by Pinbout, 12 January 2016 - 12:47 AM.


#17 gkmurrell

gkmurrell

    Explorer 1

  • -----
  • topic starter
  • Posts: 92
  • Joined: 11 Jan 2016

Posted 12 January 2016 - 01:09 AM

So it looks like roughly 280 dollars...  Probably doable.  So someone suggested getting the primary mirror "refigurred".  Is that something I would automatically need to do, or could I make a decision on that based on the performance.  Looks like both that and coating can add big $$ pretty quickly!



#18 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 12 January 2016 - 08:54 AM

you can build without getting it refigured. you can do that in a year or two.

 

those mirrors do have a rep but nothing to stop you.

 

its a big light bucket  you'll have lots of fun looking a galaxies, nebula all kinds of **** that a big mirror can deliver, just not planets. I'm jealous.

 

A smaller scope is better on planets anyway cause its less effected by seeing, the turbulent layers of air in the upper atmosphere & jet stream

 

so you don't have to get it re-figured right away, it has to be tested 1st anyway. best way to do that is to build the scope and star test it.

 

btw Steve Swayze is the least expensive.

 

here Steve is helping me test my mirror

https://www.youtube....h?v=t3UkcF4LegY


Edited by Pinbout, 12 January 2016 - 09:10 AM.


#19 jallbery

jallbery

    Mercury-Atlas

  • *****
  • Posts: 2,554
  • Joined: 01 Nov 2015

Posted 12 January 2016 - 09:15 AM

People still make classic sonotube dobsonians,   However, in a 17.5" scope, they make for a very large, bulky and very heavy telescope.  The tube is going to be over 6 feet long, and won't fit in many vehicles.  A truss-based dob is much more easily transported, particularly in that size.   However, sonotube is cheap, and is one way forward if you want to keep the spirit of the original Odyssey.  I would get a decent 2" focuser, though, rather than the modified plumbing fixture they originally provided.   But if it were mine, I'd certainly go the truss route; if that giant sonotube isn't around any more, that may very well be what your father had in mind.

 

I have no doubt that the that the Antares diagonal mentioned above is superior to the GSO one I referred to.  However, this is a Coulter Odyssey II mirror, and Coulter was very much about big bang for the buck, and not so much about providing the finest optics available.   Unless your father got exceptionally lucky, I'd guess that the GSO diagonal would almost certainly (1) out-perform the original Coulter diagonal and (2) NOT be the limiting factor in the performance of the scope.  (FWIW, GSO makes the mirrors and diagonals in many current commercially available dobsonian telescopes).  

 

Now, if you want to get the mirror refigured by an expert optician and then resilvered, then a better diagonal is probably  in order.   But if the mirror is in good shape, the GSO diagonal is probably good enough (at least in in my opinion).   You can always refigure and upgrade the diagonal at a later date, if you use the telescope enough to justify the expense.


Edited by jallbery, 12 January 2016 - 09:17 AM.


#20 tag1260

tag1260

    Mercury-Atlas

  • *****
  • Posts: 2,588
  • Joined: 07 Oct 2012

Posted 12 January 2016 - 10:35 AM

You know, there's more to it than you think. You'll may feel a sort of connection viewing with your dad's old mirror. Sometimes things like that mean more than the view itself. When you first build it, you'll be seeing pretty much the way your dad did. Yea, there are better mirrors out there or you could have that one re-done  but will they give you the same feeling?  Just a thought.



#21 jallbery

jallbery

    Mercury-Atlas

  • *****
  • Posts: 2,554
  • Joined: 01 Nov 2015

Posted 12 January 2016 - 11:27 AM

You know, there's more to it than you think. You'll may feel a sort of connection viewing with your dad's old mirror. Sometimes things like that mean more than the view itself. When you first build it, you'll be seeing pretty much the way your dad did. Yea, there are better mirrors out there or you could have that one re-done  but will they give you the same feeling?  Just a thought.

 

I think there's a lot to be said for that.  If it were a smaller Odyssey and had been my father's,  I'd even be tempted to go the sonotube route.  To me, that's what a Coulter Dob is supposed to be.   However, the tube assembly alone of an Odyssey II comes in at about 120 pound-- a truss design that breaks down is simply much more practical.   But I'd probably try to keep it more in line with the spirit of the Odyssey II (and John Dobson's original vision) and not try to turn it into a super-ultra-light design.  And I'd definitely paint it red!

 

But that's just me.  GKmurrel has to do what feels right to him.



#22 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 24,885
  • Joined: 22 Feb 2010

Posted 12 January 2016 - 11:27 AM

 

You know, there's more to it than you think. You'll may feel a sort of connection viewing with your dad's old mirror. Sometimes things like that mean more than the view itself. When you first build it, you'll be seeing pretty much the way your dad did. Yea, there are better mirrors out there or you could have that one re-done  but will they give you the same feeling?  Just a thought.

 

I think there's a lot to be said for that.  If it were a smaller Odyssey and had been my father's,  I'd even be tempted to go the sonotube route.  To me, that's what a Coulter Dob is supposed to be.   However, the tube assembly alone of an Odyssey II comes in at about 120 pound-- a truss design that breaks down is simply much more practical.   But I'd probably try to keep it more in line with the spirit of the Odyssey II (and John Dobson's original vision) and not try to turn it into a super-ultra-light design.  And I'd definitely paint it red!

 

But that's just me.  GKmurrel has to do what feels right to him.

 

 

just don't recreate that big red tube scope...the lighter, the easier to use the more often you'll use it.



#23 Steve OK

Steve OK

    Surveyor 1

  • -----
  • Posts: 1,692
  • Joined: 22 Sep 2007

Posted 12 January 2016 - 11:42 AM

I built a truss type Dob around my 17.5" Coulter mirror.  I had originally built a Sonotube scope, and, as others have said, it was a beast to try to transport and use.  After the rebuild with a carefully designed primary cell, and reliable collimation, I found I was still not satisfied with the performance.  The Coulter mirrors had a wide range of quality, apparently, with the center of the range on "OK".  Mine was in the lower part of the range, I guess.  Yours may be one of the better ones.  I eventually had mine refigured by Steve Swayze, and coated by Spectrum Coatings.  Swayze had it for 16 months, and was never able to get it completely free of astigmatism.  That said, the performance increase was wonderful, and I have used the scope more in the two years since having it "fixed" than in the previous 30 years I've owned it.  Before the refigure, it was still a lot of fun at low power for DSOs under dark skies.  After the refigure job, and with good seeing, Jupiter, Saturn, the Moon, double stars, pretty much everything...wow!

 

Steve


Edited by Steve OK, 12 January 2016 - 11:43 AM.


#24 jallbery

jallbery

    Mercury-Atlas

  • *****
  • Posts: 2,554
  • Joined: 01 Nov 2015

Posted 12 January 2016 - 11:53 AM

 

just don't recreate that big red tube scope...the lighter, the easier to use the more often you'll use it.

 

 

Yes... not intending to imply otherwise.   But perhaps something more like the Meade Lightbridge design on a traditional dob rocker box.

 

https://www.astronom...ope_p13033.aspx



#25 Chuck Hards

Chuck Hards

    You don't know Swift from Astrola

  • *****
  • Posts: 27,586
  • Joined: 03 May 2010

Posted 12 January 2016 - 12:02 PM

So it looks like roughly 280 dollars...  Probably doable.  So someone suggested getting the primary mirror "refigurred".  Is that something I would automatically need to do, or could I make a decision on that based on the performance.  Looks like both that and coating can add big $$ pretty quickly!

 

I've owned two of those Coulter 17.5" mirrors, and tested both.  Both were done very well, especially considering the cost at the time.  Better than 1/4 wave, smooth, and straight Ronchi bands.  One had a very slight hill at the center, but it would have been masked by the secondary shadow, and was probably too small to affect imagery anyway.  I sold that one, kept the other, which I still have to this day.

 

That said, I've heard of some who weren't so lucky.  If you can at least look at it with a Ronchi, you'll get a good idea of quality.




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