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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

17 inch spotplots
      #4977415 - 12/21/11 09:25 AM Attachment (193 downloads)

Here is the spotplots for a Mike Jones offaxis that I am building . I have had a 20offaxis for 2.5years and have thought this alot.Mikes design is as good as it gets .

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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: kfrederick]
      #4977438 - 12/21/11 09:37 AM

A lot of advanages to this type of telescope .And more problems seting up the tilted optics .I wont to thank all who have helped so far .All opions are welcome

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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: 17 inch spotplots new [Re: kfrederick]
      #4977535 - 12/21/11 10:38 AM

Thanks for posting. I hadn't realized just how good that design can be. How wide a field does the 0.5inch spot represent?

dan


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George Kiger
member


Reged: 05/19/06

Re: 17 inch spotplots new [Re: kfrederick]
      #4977641 - 12/21/11 11:34 AM

Can you give us the details of the design?

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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: George Kiger]
      #4977676 - 12/21/11 11:50 AM

The telescope uses a 17 inch primary mirror f8 .and a 4 inch convex secondary .And two correcting lens all surfaces are spherical except for the primary it is -1.4 conic .Mike is best to answer the spot plot question.KEVIN

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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: kfrederick]
      #4978053 - 12/21/11 03:49 PM Attachment (128 downloads)

Here's the OSLO-EDU file for Kevin's scope, with some help from David Ostwald on the coordinate translations and rotations. The spots look good anywhere over a 1" diameter FOV at focus, but I don't know how to make OSLO do multiple field points. I'll put up spots over the FOV in ZEMAX, where it's easy.
Mike


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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: 17 inch spotplots new [Re: kfrederick]
      #4978104 - 12/21/11 04:18 PM

Huge amount of awesomeness in this design. Could be why I'm building my own as well.

And many many thanks to Kevin for keeping this ball rolling, people are simply not gonna believe what they're looking through - I think Mike said "17 inch apo!".

Best,
Mark


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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: mark cowan]
      #4978183 - 12/21/11 05:18 PM Attachment (73 downloads)

Mike Jones work

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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: kfrederick]
      #4978190 - 12/21/11 05:23 PM Attachment (65 downloads)

More spot plots

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gatorengineer
Carpal Tunnel
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Reged: 02/28/05

Loc: Hellertown, PA
Re: 17 inch spotplots new [Re: kfrederick]
      #4978479 - 12/21/11 08:08 PM

Kevin,

How sensitive is it to exact spacing, and accuracy of the figure.... Some other OA designs go sideways quick with slight fabrication tolerances.

Mark


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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4978536 - 12/21/11 08:51 PM Attachment (70 downloads)

Here's the full-field spot diagram at 11 different field points, with the Airy disk shown at center. The outer circle is 30mm in diameter, and the spots and Airy disk are plotted within the circle 100X larger. As the OSLO file shows, I was able to get Kevin's design fairly well achromatized over the 0.45-0.66um spectral band, which brings indigo to near-violet light in focus as well as the usual blue-red color correction. If Kevin can make and assemble this scope as well as the design calls out, then Mark is right, the imagery should at least be semi-apochromatic in quality, and will be limited only by atmospheric turbulence conditions.

We must pay homage to Cuzzin Ed Jones here, as my design is based on his innovative Chief design. I deviated from Ed's BK7 glass choice to bring indigo and blue light in better control, and the fold mirror is convex rather than flat, but basically it's still a Chief.

I will work on tolerancing Kevin's Chief over the Christmas break and post up the results.

Mike


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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: gatorengineer]
      #4978549 - 12/21/11 08:57 PM

The primary was done by Carl Zambuto Mechanicaly holding the optics is like any other telescope they need in the correct spot The corector lens needs to be very close .If Mike gets the plots this good for a 17 inch f8 anything smaller would be perfect.So glad Mark Cowen is doing one lots of good ideas there.

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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: 17 inch spotplots new [Re: kfrederick]
      #4978807 - 12/22/11 12:26 AM

At a -1.4 conic on the primary there's not a lot of difficulty at f/8. The lenses are going to be a bit pricey but definitely worthwhile. OTOH pretty much any EPs will work well.

Best,
Mark


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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: mark cowan]
      #4979045 - 12/22/11 06:18 AM

My plan is to Take the numbers off zemax and put them in a cnc mill and make a top piece that holds the focuser/ centrated corrector lens /secondary and the laser target.to atleast.010.On First setup move the ladder or primary so the moon focuses at the correct distance from the last lens .After that only use two bolts on the primary to adjust .The primary be able to move side to side as well. The top is fixed .That is the plan for now .The secondary is ground

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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: 17 inch spotplots new [Re: dan_h]
      #4979092 - 12/22/11 07:31 AM

Quote:

Thanks for posting. I hadn't realized just how good that design can be. How wide a field does the 0.5inch spot represent?

dan



Half inch off axis for a 136 inch fl is 0.2 degrees. The 1 -inch field is 0.4 degrees - less than the Moon, which is between 0.48 and 0.57 degrees.

Mladen


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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: MKV]
      #4979144 - 12/22/11 08:09 AM

The primary is f8 the telescope is f8.647 about 90x with my 40 mm.A offaxis can go as low a power as you wont and only lose apature the obstructed you go too low the %CO gets too big. Fun messing with this in Oslo .Good work by Dave O .Thanks for posting

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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: MKV]
      #4979301 - 12/22/11 10:06 AM

Right, Mladen. As Kevin will almost exclusively use this as a visual instrument, there wasn't a need to design for a field wider than 1" diameter. It could be done, but at the expense of sharpness over the central 1" format. I have experimented with wider FOV's using a third element, but so far I have encountered diminishing returns. Ed's basic Chief design is hard to improve on! All I did here was bring a slightly wider spectral band under control. Kevin and I talked at length about the extra cost of the non-BK7 elements, and he wasn't the least bit concerned, so GOOD! Can't wait to hear about first light!
Mike


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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: kfrederick]
      #4979312 - 12/22/11 10:14 AM

Three cheers on using CNC for this scope. The tolerancing work I did last night is pretty much demanding it. This is not a scope to make with hand tools and plywood. I actually used 0.01" for all decentrations in the tolerancing before having read your thread this morning, and that's actually at the hairy edge of acceptable. You'll still need to have some alignment adjustment on the decenter and tilt of the elements.

Not surprisingly, tilt of the convex secondary is the most sensitive parameter. It will definitely need precision tilt adjustment, and that must stay fixed over the full range of telescope elevation angles.

Tolerances take a while to adjust and execute. I'll try to finish and post up tolerances over the Christmas/NY break. What I've seen so far tells me that for both elements, radii should be held to 0.1% either side of nominal, thicknesses should be within ±0.005", and element wedge should be less than 0.001".

Mike


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kfrederick
Carpal Tunnel
*****

Reged: 02/01/08

Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4979439 - 12/22/11 11:30 AM

Great work Mike. How can you make a hyperbola primary and a spherical secondary combo to work? kf

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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots [Re: kfrederick]
      #4979500 - 12/22/11 11:57 AM

In a centered system, it wouldn't work. But a Chief is not a centered system. It is a bizarre string of tilted, decentered elements, individually being figures of revolution, yet amazingly capable of phasing together to give a beautifully corrected broadband image over a small region. Like a Herrig multibounce, which is even weirder, it is hard to believe that a Chief can actually work, but as you know well Kevin, it does.

I for one am a strong believer that more of these "fringe-ey" non-intuitive wack-job telescope optical configurations still exist. They are all about delicate balancing of oblique high-order monochromatic and polychromatic aberrations over a finite "sweet spot" of sufficient optical quality. So those of you with any decent optical design program, keep on looking and experimenting. I don't think we've found them all.

Mike


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