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10" f/3.5 Astrograph with Rosin focal reducer

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#1 Mike I. Jones

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Posted 15 November 2012 - 06:40 PM

Been a while since anyone tossed a new design to the sharks here. So, give 'er the works!
Mike

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#2 Mike I. Jones

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Posted 15 November 2012 - 06:43 PM

Here are the spots. Not too bad, pretty much DL at f/3.5 over the 1.3" field diameter, 2.1 deg. angular FOV. It's color corrected over the 0.41-0.75µm band, could probably go a little wider with broadband AR coatings. Uses standard 4" diagonal mirror with 0.19" offset away from focuser and toward the primary. Primary is hyperbolic, CC=-1.8026. Just means figure it 1.8026X stronger than the equivalent paraboloid.

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#3 Mike I. Jones

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Posted 15 November 2012 - 06:44 PM

and here's the OSLO-EDU file. Enjoy!
Mike

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#4 Mark Harry

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Posted 16 November 2012 - 08:35 AM

Got it saved, thanks Mike.
***
My OSLO version says the reducer glass isn't in the catalog, and it barfs. How recent is your OSLO version?
M.

#5 Mike I. Jones

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Posted 16 November 2012 - 10:46 AM

Version 6.6. Time to update yours?
Mike

#6 Mark Harry

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Posted 16 November 2012 - 07:12 PM

6.3.3 .

Hate to mess with it, knowing my luck.
M.

#7 Mike I. Jones

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Posted 16 November 2012 - 10:01 PM

Nah, not a biggie, try it. Download the 6.6 version, install it in a new and separate folder, and you're in business. I keep my *.len files in a folder separate from any version installations so they don't get whacked.
Mike

#8 kfrederick

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Posted 17 November 2012 - 10:18 AM

This is a fast Over corrected newt with a 3 lens corrector ? Is the over correction for coma ? Oslo is great Be nice if you and others would have a link to all the oslo files posted . There must be over 100 designs . Thanks for posting

#9 Mike I. Jones

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Posted 17 November 2012 - 05:28 PM

In Rosins, you allow the primary conic constant to float to offload correction of spherical aberration from the corrector group to the primary. That leaves the corrector with more flexibility to correct chromatic and field aberrations.
Mike

#10 kfrederick

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Posted 19 November 2012 - 01:13 PM

Where can a lens be gotten ? Field aberrations? Is that coma .

#11 MKV

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Posted 19 November 2012 - 02:09 PM

Where can a lens be gotten ? Field aberrations? Is that coma .

K, there is some miniscule residual coma, but the images are still diffraction-limited for all practical purposes. Mike's Rosin corrected scope is a superb solution, both visually and photographically. It would be interesting to comapre it to Paracorr's performance.

The PSF images below show just what the stars images would look like under very high magnification. The image patch for each image is 25 microns wides, so you can see the images themselves are no bigger than 5-6 microns.

The corrector lenses can be ordered from professional companies, but they won't be cheap. Almost not worth it. They could be made using a small spindle but not by hand.

Mike: It would be interesting to see a tolerance analysis of the configuration. It's definitely a very advanced project - and very promising.

Mladen

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#12 Mike I. Jones

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Posted 19 November 2012 - 03:47 PM

Thanks, Mladen. Was beginning to wonder if you saw it. Agree, that triplet set of lenses, fully BBAR coated, would probably run $3-4K from a place like Cumberland. This design would be at the far end of any telescope bucket list of mine, if ever. But it's still fun to experiment with designs like this on cloudy nights.
Mike

#13 MKV

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Posted 20 November 2012 - 04:15 AM

Hi Mike, yes I did see it, and it's rather amazing what an extra element can do.

Depending on tolerance requirements (OSLO.edu has only limited capacity for this type of work), the corrector will probably be the priciest element of the configuration.

On the practical side, if tolerances are within amateur production capabilities (and I mean advanced amateurs!), then this project would be a lot more financially attractive - especially for big, fast mirrors!

The highly aspheric, fast, primary is another story. Making an accurate f/4 highly hyperboloidal primary requires a well tooled and experienced worker, unless custom-ordered mirrors are not a financial burden.

Speaking of tinkering on those cloudy nights, it would be interesting to do a direct theoretical comparison of this Mike I. Jones-Rosin corrected system as opposed to a 10-inch f/3.5 Newtonian with a Paracorr and a 10-inch f/3.5 Newotnian using a Wynne-type corrector (both of which are commercially available).

At any rate, seeking such solutions on cloudy nights has produced many an attractive design, and this is definitely one of them. Excellent work, Mike.

Mladen

#14 kfrederick

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Posted 20 November 2012 - 06:49 AM

Hey what about a Herring? or Hamiltonian yolo Be nice if one thread had all the designs ever posted in Oslo

#15 Mike I. Jones

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Posted 20 November 2012 - 07:16 AM

Thanks again, Mladen. I wish we all had the designs for Paracorr, ASA, etc. correctors so we could do the comparisons you say. Those are closely guarded family jewels, I'm sure. Many of us can and have designed several different Paracorr-type coma correctors that give very nice performance. But the likelihood of exactly modeling a commercial product, even if you disassembled one and took a micrometer and spherometer to it, is nearly zero. You'd have to de-bond cemented elements and measure the interior radii, and take each element and do a focus-vs-wavelength scan to try to reverse engineer the glass index and dispersion. Who's gonna want the design so bad you'd irreversibly destroy a $470 product? Not me!

I can take a look at the tolerances on this triplet Rosin. Typically, tolerances tighten up with increasing element power, surface curvature and/or marginal ray incidence angles.

Mike

#16 Mike I. Jones

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Posted 20 November 2012 - 07:25 AM

That sounds like a great thing you could do for everyone here, Kevin. Can you go back through all the ATM forum posts, and even back into the archives, and download all the OSLO files into a common folder? Organize the files into classes of telescopes, then ID gaps in the collection (like the Herrig, for example). We could talk to the CN admins about setting us up a community OSLO file for all to access and add to.

Mike

#17 kfrederick

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Posted 20 November 2012 - 09:35 AM

I have some saved already was not sure if the authors would be ok with me posting them .I like your idea I know You Dave And ED have alot .

#18 MKV

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Posted 20 November 2012 - 10:48 AM

I have some saved already was not sure if the authors would be ok with me posting them .I like your idea I know You Dave And ED have alot .

I don't think posting a list of links to the published designs would violate the TOS.

Mladen

#19 Mike I. Jones

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Posted 20 November 2012 - 10:58 AM

Hasn't everything posted on Cloudynights already been blessed by each of the authors for public domain? I don't see a TOS issue at all in going back and re-downloading OSLO designs in the forums and archives and collecting them together into a public file. Those OSLO files wouldn't have ever been posted if the authors weren't fine with doing so, right?
Mike

#20 kfrederick

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Posted 20 November 2012 - 11:04 AM

I think if the authors post what they have to share on one link would be cool .Also some info on using Oslo and what some of those big words are .Be great if more got made . Thanks for all the cool designs I am here to help .

#21 MKV

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Posted 20 November 2012 - 11:30 AM

Hi Mike. You're absolutely right about the trouble, cost, effort (never mind the ethics involved), etc. of retro-engineering registered products. What I had in mind was, of course, comparing your Rosin-type triple corrector to Paracorr and Wynne type condifugrations that have been suggested as possible close replicas of the same. In my relatively short time on CN, I remember both corrector types being mentioned and discussed, possibly some in archived files.

Mladen

#22 MKV

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Posted 20 November 2012 - 11:37 AM

Mike I was told by a mod (not you) that one may not post someone else's picture (as an example), even in context - and even if crediting the author.

Mladen

#23 MKV

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Posted 20 November 2012 - 11:44 AM

Mike, speaking of reto-engineering, some people obviously feel it's worth the effort.


http://img405.images.../es14ethos2.jpg


as seems to be the case with Ethos. Given this precedence, I am really surprised no one has come up with a Paracorr copy. Either it's not lucrative enough, or perhaps the laws have changed since this photo was taken.

Mladen

#24 Pinbout

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Posted 20 November 2012 - 04:15 PM

some people obviously feel it's worth the effort.


http://img405.images.../es14ethos2.jpg




I've always heard about that image but never saw it. Thanks

#25 Gert

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Posted 21 November 2012 - 01:00 AM

Hi Folks,

Is this configuration used by the ASA astrographs?

http://www.astrosyst...strographs.html

...
H-SERIES
The astrograph of the H-Series have a hyperbolic primary mirror...

Clear Skies,
Gert






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