180 replies to this topic

[apfever]

Speaking of which.

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[CHASLX200]

Not fitting in my Bolt.

[bjkaras]

My 1980 Odyssey 1 had a mirror that was about 1/2 wave. Total mush and lots of coma. I tell people that if you buy one it better come with test data or plan on having it refigured. 

My 10” mirror has a great figure, but there is going to be coma because it’s f/4.9. That is the cause of the coma, not the figure. Coma is inversely proportional to the cube of the focal ratio.

[starcruiser]

The arrival of the Coulter dobs marked the beginning of the modern era (and the end of the classic era) in amateur astronomy. This also meant the eventual end of many (now classic) scopes. Such is the nature of things where change is the only constant.

[Terra Nova]

The arrival of the Coulter dobs marked the beginning of the modern era (and the end of the classic era) in amateur astronomy. This also meant the eventual end of many (now classic) scopes. Such is the nature of things where change is the only constant.

Yes, and then as now such change was marked by devolution rather than evolution when it came to the Coulter dob.

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[JamesDuffey]

Just an FYI, coma has absolutely nothing to do with the figure of a mirror. 

This brings up an interesting question; do spherical and parabolic mirrors of the same foal length have the same amount of coma?

[apfever]

This brings up an interesting question; do spherical and parabolic mirrors of the same foal length have the same amount of coma?

My first thought would be no. One mirror could be large with a very short F ratio, the other could be small with a very long F ratio, both with the same focal length. I think the focal ratio at some point would come into play more than the focal length. I have no numerical knowledge on the comparison but my gut feeling is that a spherical mirror would have more coma than a parabolic of the same focal ratio. Coma in a parabaloid is well defined since it has a perfect datum point on axis to reference. I'm not sure how coma would even be defined in a sphere. Prehaps the total psf then somehow numerically subtracting the imperfect focus on axis?

 

Analysis of coma amplifying error in figure seems to be beyond the original idea of Zane's comment as well as Brian's in post #53, but it is an interesting idea.

I think the idea intended is that coma is going to exist at a set minimum based on a perfect mirror. The figure is something that can be directly controlled. 

Edited by apfever, 04 October 2021 - 03:04 PM.

[Claytoncramer]

Yes, and then as now such change was marked by devolution rather than evolution when it came to the Coulter dob.

[Claytoncramer]

That Cave Astrola is classic. I had that mount. I have since replaced it with a Losmandy GM8. The Cave mounts were mechanically disappointing. My father and I had to rebuild that Cave mount one night when the two ends of the polar axis stopped talking to each other.

[starcruiser]

Yes, and then as now such change was marked by devolution rather than evolution when it came to the Coulter dob.

Good pics showing the devolution. I had never thought of it that way before.

 

But the marketplace often mimics the same Darwinian elements of life. The new creatures (the Dobs) didn't require much food (low cost), so they multiplied in great numbers and consumed most of the food (customers money) leaving little left for the previous creatures (the classics), who needed much food (expensive) to survive. The few that survived into the modern era include the adaptable (jack of all trades) creature known as the C8 or those that found a unique ecological niche like the creature called the Questar.

[Augustus]

Yes, and then as now such change was marked by devolution rather than evolution when it came to the Coulter dob.

Show me an equatorial 14" scope that doesn't require two people to set up.....

[CHASLX200]

Show me an equatorial 14" scope that doesn't require two people to set up.....

I had a 12.5" F/7.5 i could do on my own when i was 27. But it was a pain. OTA was like 100+ lbs with a 6" finder.  But i had to stand the OTA on end and take the weights off the mount and slide it on the saddle.  But no way anyone could lift it up and get it on the mount. I may have a pic somewhere so i will look for it.  It was a heavy 16" OD Parks tube with rotating rings Scope also had a 14.5" mirror with the same FL as the 12.5". So it was a easy swap with cell and mirrior but even more heavy.

 

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Edited by CHASLX200, 05 October 2021 - 07:07 PM.

[jgraham]

Wellll, actually.... 14s are quite easy to setup...

https://youtu.be/TBawz69qo_A

I've done this and it works great!

[maroubra_boy]

Before and after...

 

Sorry, but that's the largest resolution pic I have left of the original Odyssey 2.

 

The original mount not only was it heavy, but in all honesty a dog of a mount in its action.  Didn't help that the Nylon pads were way too small, especially the alt ones.  When I got it the focuser had been changed to a nice JMI one.

 

All that is left of the original is the optics.  It also has that JMI focuser as there is nothing wrong with it at all after all these years.

 

Optically, it is astigmatic   But it does a very good job up to 250X.  I didn't make the new cell that it came with, so I can't condemn the optics until I change the cell (another project to add to the list...).

 

First light for me with the Odyssey 2 was M42 - HOLY HECK!  I could see greens, blues and pinks with it!  An image I will never forget

 

Alex.

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Edited by maroubra_boy, 06 October 2021 - 04:10 AM.

[Terra Nova]

Wellll, actually.... 14s are quite easy to setup...

https://youtu.be/TBawz69qo_A

I've done this and it works great!

I had to hold my breath several times while watching that video. I was afraid he was going to drop it the way he was swinging it around!  

[Terra Nova]

Show me an equatorial 14" scope that doesn't require two people to set up.....

A 14” equatorial Newtonian needs to already be set up!

 

 

……….in an OBSERVATORY!!!

[Jehujones]

Great comments everyone, I love this post. All valid points too. I wouldn't trade my experiences with my 10.1 for anything. Coulter allowed me to enter into the world of DSOs due to their low price. And yes, after almost 40 years I've spent money on upgrades, but it was gradual as my budget allowed. I just didn't have the cash to plunk down all at once for the scope of my dreams. Besides, EPs are an investment that aren't tied to any one scope. I had to use my scope for so long without any finder that I became an expert at pointing and star hopping my way around the sky. What a way to really learn the sky. Sure there is plenty of coma at f4.5, but the thrill of seeing galaxies like the Pinwheel, Sombrero, Bufferfly, Needle, Whirlpool...etc. on a TASCO 4.5" budget sure makes that coma go away. Towards the end of the observing night when the mirror was finally stable, I could throw on an off-axis mask and see Saturn and Jupiter at 600x with the sharpest detail. The same off-axis mask that allowed me to afford a 4" solar filter for viewing eclipses. The DIY upgrades along the way provided an education as well. Maybe that's why so many people have such fond memories of their Odyssey scopes now that we can afford the Questars.  Clear nights y'all.

[paul]

Before and after...

 

Sorry, but that's the largest resolution pic I have left of the original Odyssey 2.

 

The original mount not only was it heavy, but in all honesty a dog of a mount in its action.  Didn't help that the Nylon pads were way too small, especially the alt ones.  When I got it the focuser had been changed to a nice JMI one.

 

All that is left of the original is the optics.  It also has that JMI focuser as there is nothing wrong with it at all after all these years.

 

Optically, it is astigmatic   But it does a very good job up to 250X.  I didn't make the new cell that it came with, so I can't condemn the optics until I change the cell (another project to add to the list...).

 

First light for me with the Odyssey 2 was M42 - HOLY HECK!  I could see greens, blues and pinks with it!  An image I will never forget

 

Alex.

Hello,

Thats a great looking scope!!! 

Love to see some more pics!

Paul

[maroubra_boy]

Hello,

Thats a great looking scope!!! 

Love to see some more pics!

Paul

HA! I found some higher res pics of the Odyssey ii, and the warpaint my kids and I put on the mount and OTA

 

The second pic shows a different perspective on how massive this scope was.  The third pic shows a 50mm finder I made from a set of 7X50 binos that I cut to make a monocular - I also inserted a pair of crosshairs into the eyepiece made out of very thin copper wire.  Worked really we as a correct image straight through finder.  You will also see a second 6X30 straight through finder mounted further down the OTA.  This allowed me to find stuff when I did a big sweeping movement of the scope across the sky and I didn't need to be up a step ladder to use the finder beside the eyepiece as I could stand behind the scope to point it easily and quickly.  The larger 7X50 finder helped with final object acquisition if needed.  I've kept this idea on the new iteration of the scope as "Odessius".  I find I use the 50mm finder half as much as the smaller finder further down the OTA.

 

Alex.

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Edited by maroubra_boy, 08 November 2021 - 05:57 AM.

[Jehujones]

 I used to think that the duct tape and hose clamp mirror cell on my Coulter was pretty cheesy, but now looking at the huge mirror clips on my new Orion scope I think Coulter had something. I can't help but think that those clips degrade the image somehow. Am I overthinking it?

 

[maroubra_boy]

Another view of "Odessius" as I named the new scope with the Odyssey ii optics.

 

I have installed a Nexus DSC system to it with magnetic encoders which have 311,296 & 645,565 steps in alt az respectively.  I've taken to the sky with a 9mm plossl to test out the quality of my build - if it is not orthogonal then the accuracy will be out.  I took the scope DSO bashing from one side of the sky to the other and back again several times and the objects landed on or close to centre of this wee eyepiece each an every time!  I'm pretty happy with this result! 

 

I have taken this scope from a medieval mortar cannon to something that just about disappears into its own bellybutton.

 

Alex.

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[EJN]

The arrival of the Coulter dobs marked the beginning of the modern era (and the end of the classic era) in amateur astronomy. This also meant the eventual end of many (now classic) scopes. Such is the nature of things where change is the only constant.

 

I consider the early solid-tube dobs the semi-modern or transition era. The modern area began with this:

 

[CHASLX200]

I consider the early solid-tube dobs the semi-modern or transition era. The modern area began with this:

 

Tectron was first with the real jump in Dobs and then around 1990 Obsession and later on Starmaster and on and on.

 

I have that issue.
 

[EJN]

Tectron was first with the real jump in Dobs and then around 1990 Obsession and later on Starmaster and on and on.

 

I have that issue.
 

 

Yes, Tectron came earlier, so did Sky Designs, who used crimped ends on the truss tubes.

 

What Dave Kriege did was come up with a design where the the truss pole attachment was foolproof and required no knobs to drop in the dark - they were all captive, the low profile mirror box (compared to what came before), the large "half-moon" altitude bearings, and the use of Baltic birch plywood. Also the first to use textured formica on the bearings, it was "tweed" texture, later switched to Ebony Star.

 

The first truss tube Dob I ever saw was at the Illinois Astrofest in 1984 (see photo below). I forget the builders name, it used a 17.5" f/4.5 Coulter mirror (so is relevant to this thread), with a UTA which was octagonal, made of fiberglassed styrofoam with aluminum hard points where the tubes, spider, & focuser attached. The side bearings were from Novak, and the truss tubes were crimped at the ends. Needed 16 knobs to attach the truss poles, and the ends were numbered to make assembly repeatable. It won an award.

 

And the guy in the black T-shirt behind it looking at it is (the late) Pete Smitka, who later founded Portaball.

 

I scanned this from the color negative of the picture I took, this was right next to where I was camped.

 

 

Edited by EJN, 18 November 2021 - 09:58 PM.

[clamchip]

I miss every one of my Odyssey's I've ever owned especially my 17.5 I have had

more wow's and smiles from the Coulter Odyssey than any other telescope.

Here's a old photo I just finished cleaning my 17.5 mirror in the kitchen sink, look at the size of it !

Yes that is a dishwasher below the mirror and yes that thought did cross my mind !

Robert