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Equipment Discussions >> ATM, Optics and DIY Forum

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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
*****

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
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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 new [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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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: mark cowan]
      #4979519 - 12/22/11 12:05 PM

Right Mark, it's not a challenging conic to make. Based on Kevin's project and our recent telephone conversation, Carl has already modified his analysis spreadsheet to enable him to properly figure mirrors with conic constants other than paraboloids. Knife edge shifts are simply multiplied by the conic constant, and Carl figures the mirror to have the scaled shifts between zones. A paraboloid has a conic constant of exactly -1. A hyperboloid with conic of -1.4 just means that the KE shifts for the equivalent paraboloid are scaled up by 1.4X. The same goes for Dall-Kirkham primaries, with conic constants ranging between zero and -1. This opens up a mirror maker's capabilities to Rosin, Ritchey-Chretien and Dall Kirkham primaries as well as traditional paraboloids.

Mike


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Benach
Pooh-Bah


Reged: 01/24/08

Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4979631 - 12/22/11 01:09 PM

Mike: To answer your request, I have worked a bit on ESA's COROT mission and the primary telescope is also a TMT with a correction system, so there you have another example of a weirdo scope.

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

Reged: 06/03/05

Loc: salem, OR
Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4979697 - 12/22/11 01:44 PM

Quote:

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".




Is this absolute or can the spacings be adjusted to accommodate as-manuf actual specs? Both Kevin (I think) and myself are just planning to have these lenses made commercially.

My other question is (obviously) going to be about coatings - we've all seen the kind of charges for small qty coatings on lenses. With 4 surfaces what would any tradeoff look like?

Finally, since I'm already planning to manufacture large fast hyperboloids the quartz primary will be more like a vacation.

Best,
Mark


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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4979753 - 12/22/11 02:19 PM

Quote:

s 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



Oh that goes without saying, Mike. Ed's configuration is awesome, even if the angular image field is somewhat restricted. It should be mentioned that its performance off axis is better than a classic paraboloid of the same aperture and focal length. Likewise, Ed's design is more compact than a classic Newtonian version.

The only thing I see as being somewhat more of a challenge is (1) the hyperboloidal primary, and (2) the fact that Ed's design is a compound system. As such it would have to be figured at the focus by autocollimation or interferometry. So, a lot more work than an ordinary Newotnian.

Mladen


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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: MKV]
      #4980152 - 12/22/11 06:22 PM

Much thanks for the cool telescope .The best image I have seen was in my 20 f8 chief[ED Jones design] .Mark Harry is helping with testing of the secondary and lens .I have the best in the design and optics .The bigest problem is the perfect structure .Thanks to the "Jones" for this unreal unobstructed reflector design. It does work!

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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: mark cowan]
      #4980192 - 12/22/11 07:04 PM

Right Mark, I plan to be standing by as Kevin gets his optical elements finished, starting with Carl's finished primary radius and conic, and then as the lens elements are finished. The convex secondary should likely be finished last, as its radius and tilt angle can be modified slightly to peak up the final design performance.

The tightest tolerances are required if one were wanting to build perhaps 100 or 200 of these Chiefs in production, and didn't want to have to spend labor hours mixing and matching lens elements and secondaries in each assembly. But, 0.1% on radii, ±0.005" on thicknesses and wedge <0.001" are not unreasonable specs for quality lens suppliers, provided the manufacturer has test plates and metrology to guarantee precision and quality control.

These tolerances can be relaxed by perhaps 2X or 3X as long as the secondary is done last and can be tweaked to compensate, then all the tilts and decenters optimized using all finished components.

Mike


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gatorengineer
Carpal Tunnel
*****

Reged: 02/28/05

Loc: Hellertown, PA
Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4980320 - 12/22/11 08:46 PM

Guys,

I admire the energy and enthusiasm, and investment. But I really have to wonder if a scope like this is truly buildable..... I was ready to go on a traditional 8 F8 chief, until I really got into the necessary tolerances for fabrication, which were less than 1/8".... Which being a plywood guy is about the limit of my skills.

A scope requiring 0.01, or thereabouts isnt even aluminum because of thermal expansion issues, its Carbon Fiber..... Then when you figure in the need to hold that from horizon to zenith, well.... Its an impressive undertaking in a large scope....

Perhaps I am just not understanding....

To me studying all of the alternate designs out there, I continually wonder why there arent alot more large (10" and bigger) Schupmans out there....


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Ed Jones
Carpal Tunnel
*****

Reged: 04/06/04

Loc: Sin-sin-atti
Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4980364 - 12/22/11 09:19 PM

Mike,
Great design as usual! It looks to be a Chief version of a hyperbolic Newtonian except with a convex secondary. This goes to show that there are a bunch of designs that have both a Newtonian and an unobstructed Chief analog. This design has good correction for coma. My only criticism is the 7 degree field tilt which is higher than most Chiefs.

The tolerances may not as severe as you think. I haven't done any tolerancing but guessing that it shouldn't be a lot different than the Chief's I've built. When you do tolerancing you can use the primary tilt as a compensator as well as rotation of the lenses as a group. The Y centration of the lenses relative to each other is critical and needs an accurate cell but I make this adjustable to simplify things. In the Chief small lens radius errors cause mainly a little bit of CA.


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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: Ed Jones]
      #4980805 - 12/23/11 07:10 AM

I think building the structure will be fine The top piece is small 4.5x28 inches It has to hold The 4 inch secondary two lens and focuser and laser target .If that is made correct then it is like making a newtonian .The f8 optical system is very easy to keep in focus and that has to be seen to understand f8 rocks This will do deep sky great. Black sky .Only two small lens and go unobstructed .Very excited and thankfull for the design work. What you think of calling it a "MTT" Mike Tilted Telescope??

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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: kfrederick]
      #4982498 - 12/24/11 08:43 AM

Mike Was looking at testplates at http://www.optimaxsi.com/Resources/TestPlateLibrary.php and they have some close I thought if i ask for a quote it it would be less if we match there testplates work .For the second lens they have a 973.212 mm and a 534.228 That is the hardest lens to make .The first lens they have a 1232.70 .Mark Harry and I can do them if it doesnot work out ,Having them made. Any body know of other lens makers that might be usefull .Thanks hope more will try one.

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wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4984793 - 12/25/11 09:07 PM Attachment (49 downloads)

My OSLO version doesn't have neither of the two Ohara glasses used for this system. The close Schott analogs, LASF3/PSK52 produce similar result (with a bit of tweaking). Even simpler Schott glasses work well, including combinations with one lens being BK7 (example attached). So there is some flexibility with respect to glasses that can be used.

This type of corrector is probably the best ATM choice for catadioptric tilted elements telescope, but there is a price to pay. Achieving unobstructed design by adding more elements is never a clear gain. It is not only the added fabrication requirements, it is also the increased difficulty of achieving and maintaining near-perfect alignment. In this particular system, axial polychromatic Strehl for perfectly fabricated and aligned lenses in the 450-660nm range is 0.96 (BK7 version), comparable to 14% central obstruction (diameter). Less than perfect fabrication/alignment could easily make it comparable to ~20% c.o., which is achieavable in this aperture size. The likelihood of larger average alignment error for monochromatic aberrations comes extra. That's the reality of it.

Vla


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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: wh48gs]
      #4984915 - 12/25/11 11:36 PM

Via You have to admit. Mikes design is very good.Maybe better than anything in 17 inch .All for two little lens and a fancy holders .Thanks for the work .All good

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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: 17 inch spotplots new [Re: kfrederick]
      #4985022 - 12/26/11 02:19 AM

Quote:

Mikes design is very good.Maybe better than anything in 17 inch .All for two little lens and a fancy holders .Thanks for the work.



No one questions Mike's design. But Vla makes a valid point. It's one thing to compare theoretical designs; it's an entirely different thing to make valid comparisons of finished products.

The only way to truly compare two configurations realistically is to make them of the same quality and test them next to each other under identical conditions - at the focus.

The rest is just theory that cannot predict all the complicating factors of fabrication that will determine the actual final image quality. And, the shape of the wavefront converging to a focus is what matters in the final analysis.

Clearly, "Chiefs" have a distinct advantage of being somewhat more compact than your ordinary Newtonians. Beyond that I am not aware of anyone making a direct aperture per aperture, same quality, direct scientific comparison in the field.

Mladen


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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: MKV]
      #4985110 - 12/26/11 07:01 AM

Mladen I have a 20 f8 Chief for 2.4 years and have a 20 f5 newt for over 20years .That compairson has been done .This design CAN give a better image than anything .The unobstructed has many good points that is not reflected in the plots .F8 optical system Great stray light control /no dew problems .lots of back focus .I understand what your saying about it being harder . There are many designs that are worth trying for the ATM .Thanks for your time

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Dave O
sage
*****

Reged: 12/21/11

Loc: Sri Lanka
Re: 17 inch spotplots new [Re: kfrederick]
      #4985162 - 12/26/11 08:29 AM

I think one thing that should not be forgotten is that Mike's design offers a well corrected field of 1 inch diameter; better than that of an uncorrected Newtonian of similar aperture and focal length. When you add correcting lenses to the Newtonian, you will likely have to increase the central obstruction to accommodate them.

Another advantage of Mike's design is that access to the eyepiece is much better. A 17" f/8 Newt with minimum obstruction will place the diagonal about 10' from the primary mirror -- a pretty good reach for most of us.

What Mike has done is:

1) provided an excellent usable field of 1 inch diameter;
2) eliminated the Central Obstruction; and
3) provided improved access to the eyepiece in a 17" f/8 telescope...

... if everything can be kept in alignment ...

Dave O

Edited by Dave O (12/26/11 09:13 AM)


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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: Dave O]
      #4985247 - 12/26/11 10:06 AM

Dave O thanks for puting Mikes Zemax design in OSLO . Not sure if that has been done .The Oslo spot plots are done by Dave O using Mikes numbers .Great to have that tool .

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Mike I. Jones
Post Laureate
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: wh48gs]
      #4985668 - 12/26/11 02:48 PM

If you don't have the glasses used in this scope, you need to upload the latest version 6.5.4 of OSLO-EDU at http://lambdares.com/education/oslo_edu. It's freeware, so there's no reason to have an out-of-date version of it.
Mike


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Mike I. Jones
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Reged: 07/02/06

Loc: Fort Worth TX
Re: 17 inch spotplots new [Re: Dave O]
      #4985670 - 12/26/11 02:53 PM

Thanks Dave, but credit should be given where properly due. Ed Jones invented the basic Chief design concept of tilting the primary, folding with a flat, and correcting the beam with two weak tilted/decentered figure-of-revolution lens elements. I merely improved it slightly to open up the spectral band and sharpness over the FOV by (1) going to more exotic glasses and (2) allowing the fold flat to take on a spherical radius.
Mike


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DAVIDG
Post Laureate
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Reged: 12/02/04

Loc: Hockessin, De
Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4985709 - 12/26/11 03:28 PM Attachment (20 downloads)

I think credit needs to be given to Dick Buchroeder as well. Dick published an article back in 1971 Jan. Sky and Telescope "CHT: A Catadioptric Herschellian Telescope with Tilted Components". Dick's design uses the same concept with two lenses to corrector for the astigmatism and both lens have equal but opposite internal radii, they are also decenterd slightly. Dick's design also uses a flat to bend the light path. Dick's design differs slightly in the lenses are weak menicus in shape vs having plano backs.

- Dave


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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots *DELETED* new [Re: DAVIDG]
      #4985731 - 12/26/11 03:44 PM

Post deleted by kfrederick

Edited by kfrederick (12/27/11 01:20 PM)


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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: kfrederick]
      #4986541 - 12/27/11 07:46 AM

Ed Jones is who helped build and design my 20 f8 and where I got the offaxisitis .Mike changed everything/ the conic on the primary the secondary having power The lens have curves an the both sides .and diferent glass and all the decenters .Having this in OSLO is great .Great we can get designs like this .[THANKS]The spec for flex is no more than a cassagrain . Lens spec no more than a refractor .The only differents is it is not centered and tilted .At least no can say it canot work better then a newtonian the spot plots for this 17inch is half that of a 8inch newt. I think . kevin

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kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: 17 inch spotplots new [Re: kfrederick]
      #4987009 - 12/27/11 01:47 PM

The first guy to work on this was FREDERICK William Herschel So it looks like a "Frederick" worked this before the "Jones"

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MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: 17 inch spotplots new [Re: kfrederick]
      #4987042 - 12/27/11 02:12 PM

After reading all this, I honestly wonder why there are no commercially available "chiefs".

Mladen


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kfrederick
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Re: 17 inch spotplots new [Re: MKV]
      #4988006 - 12/28/11 06:34 AM

Miaden Why aint NASA calling?

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Mike I. Jones
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Re: 17 inch spotplots new [Re: kfrederick]
      #4988210 - 12/28/11 10:20 AM

My guess is that they just take more time and money to make properly than you could ever turn a profit from. A scope like Kevin is building could easily cost $20K or more each to produce commercially. Some designs are probably just best left to advanced amateurs with the skills and tools to build them. These are the kind of scopes that make going to telescope meets and star parties so worth it!
Mike


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Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4988627 - 12/28/11 02:57 PM

Quote:

My guess is that they just take more time and money to make properly than you could ever turn a profit from. A scope like Kevin is building could easily cost $20K or more each to produce commercially. Some designs are probably just best left to advanced amateurs with the skills and tools to build them. These are the kind of scopes that make going to telescope meets and star parties so worth it!
Mike



What about smaller ones, say 8 - 12-inch scopes? They would certainly fall in the "affordable" range, wouldn't they? And never having looked through a "chief", I am still curious about the specifics as regards their reputed superiority.

As I said earlier, I can definitely see the advantage of "chiefs" having a somewhat more compact tube configuration and a more accessible eyepiece. But other reasons mentioned are a bit confusing. Someone mentioned the fact that they are f/8 (?). Others pointed out that this particular design has a one inch FOV. Well so does an f/8 CDK in a much more compact package without decenter or tilting. The only downside to an f/8 CDK is a 40% linear CO.

But for planetary views slower focal ratios are desirable, say f/18-f/20 for Cassegrains, with CO's of less than 20% of linear aperture, which is doable. Owners of such scopes (Mewlons or Classical Cassegrains, for example) say they are unbeatable.

Then there is a whole different issue with large telescopes, beginning at about 18 inches and becoming progressively worse with large apertures and it has to do with speckling, regardless of the design or central obstruction, so I am not exactly sure where or why 20-inch f/8 "chiefs" would surpass 20-inch f/15 Cassegrains or f/5 Newtonians.

Thanks.

Mladen


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Re: 17 inch spotplots new [Re: MKV]
      #4988712 - 12/28/11 04:05 PM

Miaden Can you show anything[on paper]17inches that will give better visual image? I say congrads to Mike for this GREAT design .and posting the numbers in OSLO for anyone to check out and make .

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Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4988926 - 12/28/11 06:16 PM Attachment (56 downloads)

Quote:

If you don't have the glasses used in this scope, you need to upload the latest version 6.5.4 of OSLO-EDU




I have both, EDU (which does have the Ohara glasses) and Light. For some reason, it is the latter, apparently older, that opens external OSLO files. The good thing about it is that it made me try different glasses. I played a bit more with your design, and found that the corrector can be made of BK7/BASF12 (about 2.5 times the price of BK7) combination, with the radii on the two lenses identical (attached). That makes the fabrication cheaper and easier. The system is not fully optimized, but I'd say is real close.

Vla


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Re: 17 inch spotplots new [Re: kfrederick]
      #4989598 - 12/29/11 06:40 AM

Quote:

Miaden Can you show anything[on paper]17inches that will give better visual image? I say congrads to Mike for this GREAT design .and posting the numbers in OSLO for anyone to check out and make .



Mike's and Ed's designs are superb. My questions were not meant to offend anyone or to critiques their design. Far from that! My questions were about the reasons for the (non)availability of "chiefs" on the market, and also about specific issues mentioned. In other words - why make a "chief"?

As for anything "better" on paper, that depends on what you think is "better". To me "better" is what's more practical. If it's compactness, I'd say field-corrected Cassegrains; if it's ease of production, alignment, etc., then field-corrected Newtonians, keeping central obstruction for both at 19% or less, which is hardly noticible over unobstructed. Besides, it's a moot point because at larger apertures the image will hardly ever be a sharply defined Airy disc.

Mladen


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Re: 17 inch spotplots new [Re: wh48gs]
      #4989653 - 12/29/11 07:57 AM

Via That is good to know. The glass cost on this is not too bad having a matching surfaces is good also . Nice to have in Oslo so more can see .This is not much harder than making a newt just two small lens and mounting them .

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Re: 17 inch spotplots new [Re: MKV]
      #4990258 - 12/29/11 02:19 PM

Quote:

Mike's and Ed's designs are superb. My questions were not meant to offend anyone or to critiques their design. Far from that! My questions were about the reasons for the (non)availability of "chiefs" on the market, and also about specific issues mentioned. In other words - why make a "chief"?




Well, that's easy. Two parts - too new, and an "unknown" market appeal.

The apparent difficulty of physical alignment is a bugaboo, but the work that Kevin's doing with CNC punched alignment boxes should go a long ways. Still, there's not a lot of incentive to bring these to large production unless people want to buy them and can handle them consistently in the field.

For myself, I just want to build one to have, use, and show off. I don't want to build them to sell, ship, and support. From a mirror perspective the primary in any version is extremely simple, hence not much profit there - but the purchased (or custom made) bits are still relatively expensive.

I suspect the people who are interested in something like this are already capable of rolling their own.

Best,
Mark


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Re: 17 inch spotplots new [Re: mark cowan]
      #4990558 - 12/29/11 04:46 PM

Agree Mark. I have lost count of the number of awesome one-of-a-kind telescopes Jerry Logan has brought up to Riverside over the decades. You will never, ever see any of those scopes made commercially. Yet, the optics are always simply first-prizeworthy spectacular, due to Jerry's extraordinary skills in working optical parts.

That's the most fun of telescope meets to me, to see and view through beautiful, unique scopes that will never get a part number or a price tag, and are as well made optically and mechanically as any commercial products. Kevin's 17" "apo" is going to get long lines at star parties for sure!

Mike


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Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4990905 - 12/29/11 07:49 PM Attachment (32 downloads)

Mike,
I think I would prefer this design to build. By making it a bit slower (f/9.5) you can get more of a fold and a lower eyepiece; about 4 feet from the primary to the focus. This is an analog to the RC and uses an aspheric secondary and hyperbolic primary. The secondary conic is nearly -800 but because it is very flat the aspheric deviation is only about .36 microns; not much figuring needed. It has zero field tilt and no coma. Other glass types can give only a minor improvement over the BK7 used here.


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Re: 17 inch spotplots new [Re: Ed Jones]
      #4990921 - 12/29/11 07:59 PM Attachment (55 downloads)

Sweet! Put up prescrip? Here's the one I did for Kevin, in ZEMAX format. If Carl Zambuto wasn't already so far along with Kevin's mirror I'd say give he ought to give it a whirl.

I'm trying to talk Kevin into making two identical copies of his SuperChiefs and make Chiefoculars! Imagine the view through 17" aperture apo binoculars! Drool slobber...
Mike


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Re: 17 inch spotplots new [Re: Mike I. Jones]
      #4991026 - 12/29/11 09:14 PM

I have a 17 f9.4 my 20 f8 chief mirror .What if you used a 17inch circle on the one side of the mirror that[ the corrector is on] off apture/ ofaxis could be very short.Or if you moved the secondary in the inconing light path .just a little .Not much more than a edge clip.Just ideas maybe not good ones .

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Re: 17 inch spotplots new [Re: kfrederick]
      #4991037 - 12/29/11 09:24 PM

Or use a 17 inch circle on the side of my 24 f8.6 .might be very short.Looks like you are calling it a Super Chief .

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Re: 17 inch spotplots new [Re: kfrederick]
      #4991371 - 12/30/11 01:47 AM

Wow -- just gets better all the time. Nice tweak you made there Ed.

I too, think that a ~4' separation between the primary and the focal plain is "just about right" for comfortable viewing. BK7 lenses is a plus as well -- that glass is very stable and easily procured. Are they off-the shelf? If custom, could you get matching radii?

Very nice improvement on an already superb design. Dave O


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Re: 17 inch spotplots new [Re: Dave O]
      #4991524 - 12/30/11 06:15 AM

HOW could you make a -800 convex conic secondary the edge is turned up 800x over a spherical .Having all spherical secondary optics is great .Any good lens maker can do them .

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Re: 17 inch spotplots new [Re: kfrederick]
      #4991567 - 12/30/11 07:43 AM

This secondary is no different than making a Cass secondary, those who have made a Cass would have no trouble. But this may not be everyone; if anyone is really interested PM me and I can send a prescription.

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Re: 17 inch spotplots new [Re: Ed Jones]
      #4993536 - 12/31/11 08:43 AM

Ed will yours work with a f8 -1.4 conic primary ?What was the RC on your secondary? I went with f8 to keep it shorter.The good glass only costs less than a eyepiece more. On Mikes Design it helps a good bit.The thing I like on yours is the lower eyepiece and the field tilt .AtF 9.5 It is harder to get low power with avaible eyepieces.95% of the time It will be used for deep sky at 100x The 20f8 chief rocks deepsky.

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Re: 17 inch spotplots new [Re: kfrederick]
      #4993655 - 12/31/11 09:58 AM

Kevin,

Quote:

The good glass only costs less than a eyepiece more.




A glass is only as good as the correction it delivers. Spots in Ed's modification are tighter than in the original Mike's design, even if the corrector is "only" BK7. In fact, Ohara glasses would not qualify for the technical definition of an apo, because the error in the violet g-line is larger than 1/2 wave (0.65 wave). On the other hand, this same system with the Schott analogs satisfies the apo definition. The respective photopic polychromatic Strehl at best focus is 0.957 and 0.964, which would make both apo-corrected, if the criteria is (more reliable) 0.95 Strehl minimum.

Oddly enough, the best polychromatic Strehl - 0.967 - has the BK7/BASF64A combination, despite having g-line error somewhat larger than Ohara glasses. This is compensated by a tighter focusing of the other wavelengths.

Vla


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Re: 17 inch spotplots new [Re: wh48gs]
      #4993722 - 12/31/11 10:41 AM

Eds design is f9.5 And has a secondary that would be imposible to get 1/20th wave cheaply! The CONVEX edge has to be turned up alot .I am folowing Mike Jones design .No complated to .get 1/20 wave optics All sherical secondary optics .Glad you are looking at this and your work! Via Mike had not goten your numbers to work in Zemax as of yesterday .not sure why. good fun

Edited by kfrederick (12/31/11 11:41 AM)


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Re: 17 inch spotplots new [Re: kfrederick]
      #4993925 - 12/31/11 12:08 PM Attachment (33 downloads)

Quote:

will yours work with a f8 -1.4 conic primary?


This primary is F/8.19 and could probably be scaled to work except the conic is -2 and would require refiguring.
Quote:

The CONVEX edge has to be turned up alot



Hardly, if you read my post I said the secondary aspheric deformation is only 0.36 microns. One fringe of HeNe light is 0.315 microns, so it's similar to a typical Cass secondary. No this isn't an easy design but anyone familiar with making a Cass secondary could make this one.
Color is good over the whole visible range:


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Re: 17 inch spotplots new [Re: Ed Jones]
      #4994172 - 12/31/11 01:59 PM

Ed I read it as 36 micron looks like it was .36 micron .My mistake .How big is your secondary? And the overall length of the telescope .The primary is in polish and could be corrected more.

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Re: 17 inch spotplots new [Re: kfrederick]
      #5003935 - 01/06/12 09:27 AM

Looking at EDs design I would have little chance geting it to work .Mikes design will give me the best chance. As for saving a a fiew dollars on bk7 lens NO.If Zemax says s-lah53 and s-phm53 works best that is what will be used .This is alot of work to do away with the obstruction but I know it is worth it for me to try. kevin

Edited by kfrederick (01/06/12 07:36 PM)


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Re: 17 inch spotplots new [Re: kfrederick]
      #5006478 - 01/07/12 11:30 PM

http://photonics.com/BuyersGuide.aspx lots of lens makers listed here

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Re: 17 inch spotplots new [Re: kfrederick]
      #5008488 - 01/09/12 07:56 AM

Kevin,

Quote:

Via Mike had not goten your numbers to work in Zemax as of yesterday .not sure why.




Judging on Mike saying that he needed help to convert Zemax coordinates to OSLO, the two programs use different conventions and/or interface. So, proper conversion from OSLO to Zemax is also needed.

If a system works in OSLO, there is no reason it wouldn't work in any other raytracing program.

Vla


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Re: 17 inch spotplots new [Re: wh48gs]
      #5008551 - 01/09/12 09:11 AM

Right - software implementation of tilts and decenters is THE most poorly standardized aspect of every optical code I've ever used. You just have to keep practicing with a particular code's method until you more or less master its own way of doing it. CODE-V, SYNOPSIS, ACCOS, SIGMA, ZEMAX, and OSLO all do it differently. Of the lot, and I've used them all, I actually prefer CODE-V's.

What all modern optical codes need is (1) a standardization of translation and rotation sign and order conventions, and (2) a graphical method using a pop-up GUI screen that shows users in advance what will happen to the surface, element or group if certain orders of tilts and decenters are applied. The GUI would show the before/after position and orientation of the selected surfaces, with exaggeration in the case of small angles or shifts that are hard to see.

If for any optical design, its tilts and decenters are entered properly for any different code, then you are right, they should and actually do give essentially identical analysis results. But getting there can be quite a learning experience.

Mike


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Re: 17 inch spotplots new [Re: Mike I. Jones]
      #5009236 - 01/09/12 04:10 PM

Via you can see why I am so excited in this type of telescope , Hope many will try one !As more are built and improved. it only gets better .Mike what does the chiefocular look like? Kevin

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Re: 17 inch spotplots new [Re: Mike I. Jones]
      #5012512 - 01/11/12 04:27 PM

Quote:

What all modern optical codes need is (1) a standardization of translation and rotation sign and order conventions...




It would be very practical to have a standardized "simple" option - and that would be easier to implement - without all the bells and whistles attached to their different conventions, that can make conversion from one program to another a nightmare. But doesn't seem as if it will be happening any time soon.

Vla


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Re: 17 inch spotplots new [Re: kfrederick]
      #5012517 - 01/11/12 04:30 PM

Go for it, Kevin - it is always more of a trill to try something different, even if it is more challenging (or maybe because of that).

Vla


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Re: 17 inch spotplots new [Re: wh48gs]
      #5012607 - 01/11/12 05:47 PM

Only the primary will need moved .Up and down to set the focus the correct distance .Side to side to line up the laser on the center of the primary then tilt so the laser reflection off the center of the primary and hits the laser target mounted on the top .Get the top set correct[ Laser target secondary mirror, two lens and a focuser the only thing to move is the primary .As easy as a newt if the top is set .

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Re: 17 inch spotplots new [Re: kfrederick]
      #5042137 - 01/28/12 08:51 AM

Can any one post the spot plots fot a 17 inch f4 and f8 newtonian to the same scale as Mikes .Got some finished lens prices not too bad. Hope more will try one .Bet a 14 inch f8 would be nice size

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Re: 17 inch spotplots new [Re: kfrederick]
      #5074268 - 02/15/12 06:29 PM

http://apod.nasa.gov/apod/astropix.html no spikes with this telescope

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Re: 17 inch spotplots new [Re: kfrederick]
      #5100692 - 03/02/12 09:40 AM

The primary is done . Carl Z nailed the RC 272.06and the hyberolic curve is very close .The lens need to be done next think I will buy them .If any one wants to go together now is the time to say so as there are 4 test plates to be made includes the secondary.17 INCH APO for two little lens . This telescope should be able to see some of jupiters smaller moons.

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Re: 17 inch spotplots new [Re: kfrederick]
      #5100886 - 03/02/12 11:31 AM

The mounting of two lens and a secondary mirror in a box is easer to hold correct and block stray light.In many ways a Chief is easer to make than a newt just the newt has been perfected .The primary needs to be perfect or just make a newt.

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Re: 17 inch spotplots new [Re: kfrederick]
      #5224699 - 05/16/12 07:41 AM

A update on the 17inch unobstructed WB chief .The primary is done .The design has changed, the lens glass has changed as the secondary . The lens are being finished and coated by a top lens maker .Mikes new design is even better .Dave O has been helping me make a top end for a friends 10inch chief This has shown me sone cool ideas .That I will use on the 17 inch W B CHief . The 10 inch chief is nice as it uses off the shelf lens and a standard long f newtonian primary and a flat secondary.Mike tweeked the design for the 10inch chief.I will post a pic of the top end . Thanks for the help it is needed Kevin

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Re: 17 inch spotplots new [Re: kfrederick]
      #5286389 - 06/24/12 08:30 AM

The lens are finished and Mike gave me the RC for the secondary .The design is better than the first spotplots posted .Very excited to work on this .

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Re: 17 inch spotplots new [Re: kfrederick]
      #5315498 - 07/13/12 07:04 AM

All the optics are done for the W-B CHief . The 17 inch f8 hyperbolic primary was done by Carl Zambuto . The spherical secondary optics were finished by Cumberland Optical . Thanks to Mike Jones for all the help on this great design . Hope more will try a chief .

Edited by kfrederick (07/13/12 07:06 AM)


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Re: 17 inch spotplots new [Re: kfrederick]
      #5316787 - 07/13/12 11:27 PM

How long will it before it rolls out under the stars???

Best,
Mark


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Re: 17 inch spotplots new [Re: mark cowan]
      #5316834 - 07/14/12 12:19 AM

Mark Not sure yet. But having A world class design and the matched set of optics for it a big step.I do not have to prove it works better than any 17 inch design Zemax and Oslo already have. Very cool to work on this .

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Re: 17 inch spotplots new [Re: mark cowan]
      #5361472 - 08/10/12 10:39 AM Attachment (32 downloads)

Here is the OSLO spot plot for the finished Set of optics for a 17 inch unobstructed Reflector.The light looks happy .

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Re: 17 inch spotplots new [Re: kfrederick]
      #5361508 - 08/10/12 11:06 AM Attachment (34 downloads)

One more

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Re: 17 inch spotplots new [Re: kfrederick]
      #5362527 - 08/10/12 09:49 PM

That should work.

Best,
Mark


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Re: 17 inch spotplots new [Re: mark cowan]
      #5364818 - 08/12/12 02:24 PM

Kevin,

You are continuing to push the designs, many kudos.... What is the sensitivity of positioning and alignment? I have seen some designs that at a spacing error of 0.05" the design turns to peanut butter....

Thanks and looking forward to seeing it under the stars soon.

Mark


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Re: 17 inch spotplots new [Re: gatorengineer]
      #5364898 - 08/12/12 03:16 PM

Mark Any good machine shop should be able to do that with the top five things . But for sure not easy with the tilted offset lens . I could not do any of this without a CNC machinist . More ATMs should try one .

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Re: 17 inch spotplots new [Re: kfrederick]
      #5364980 - 08/12/12 04:28 PM

I dont disagree with the machine shop, my personal ATMing is limited to a compount slide miter and a tablesaw. When It builds in to an 1/8" cumulative tolerative, I feel fantastic. More often the cumulative tolerances are more... But as you say another great project.... Looking forward to the results.

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Re: 17 inch spotplots new [Re: gatorengineer]
      #5366010 - 08/13/12 08:05 AM

The Chief Corrector is no different than a Eyepiece, Coma Corrector or Barlow lens .The lens are held correctly in a machined cells .Having the design is 99.9% of making one.And Mike has given us that .My 20f8Chief works with ply board cell so they cannot be that bad .Having a working chief to use is great as I can move a lens and see what happens . All for fun .

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Re: 17 inch spotplots new [Re: kfrederick]
      #5384925 - 08/24/12 04:55 PM Attachment (23 downloads)

Got some parts for the 17 Wide Band CHief today .

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5384998 - 08/24/12 06:00 PM Attachment (18 downloads)

Interlocking box for the top . Slots hold the optics

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5389685 - 08/27/12 12:27 PM Attachment (15 downloads)

Top box with lens holders All 1/8 inch aluminum .CNC water jet did the work .

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mark cowan
Vendor (Veritas Optics)
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Reged: 06/03/05

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Re: 17 inch spotplots new [Re: kfrederick]
      #5389835 - 08/27/12 02:05 PM

Kevin, what's your prediction for having this thing together? The suspense is killing me at this point...

Best,
Mark


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kfrederick
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Re: 17 inch spotplots new [Re: mark cowan]
      #5390921 - 08/28/12 06:33 AM

Hi Mark It should not take too much time. I have all the pieces . Problems may come up .But it should go together soon This is to try out some ideas . The inside of the box could be used as a mold and the top could be carbon fiber . Thinner aluminum could be used .Or One could get carbon fiber interlocking box water jet out . Happy times

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5512781 - 11/10/12 07:46 AM

I had first light on the 17 Wide Band CHief. It works very nice .Thanks to Dave Mike and ED For there part in making this.

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Dave O
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Reged: 12/21/11

Loc: Sri Lanka
Re: 17 inch spotplots new [Re: kfrederick]
      #5513906 - 11/11/12 01:19 AM

Post some pics when you get a chance.

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kfrederick
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Re: 17 inch spotplots new [Re: Dave O]
      #5514033 - 11/11/12 06:59 AM Attachment (13 downloads)

The secondary optics

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5514054 - 11/11/12 07:48 AM Attachment (17 downloads)

The top box holding the tilted secondary and corrector One way to think of the setup is the secondary and primary in phase when the laser hits the two spots. a very tight spec but easy to achieve .

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5514722 - 11/11/12 04:18 PM Attachment (14 downloads)

The bottom

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5514724 - 11/11/12 04:19 PM Attachment (13 downloads)

Primary cell

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5514759 - 11/11/12 04:38 PM Attachment (15 downloads)

The 26 inch mounting used for the 17 inch WB Chief

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mark cowan
Vendor (Veritas Optics)
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Reged: 06/03/05

Loc: salem, OR
Re: 17 inch spotplots new [Re: kfrederick]
      #5514775 - 11/11/12 04:48 PM

How well does it work, then????

Best,
Mark


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kfrederick
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Re: 17 inch spotplots new [Re: mark cowan]
      #5514807 - 11/11/12 05:10 PM

I have only used it one time I have some mechanical tweaking to do it focuses very nice . Just like using the newt . I need to do a mounting but the optical train is done . Very happy to see it focus

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5530811 - 11/20/12 06:49 PM Attachment (19 downloads)

Took this pic with my cell phone with the 17inch chief

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5533735 - 11/22/12 10:55 AM

Making the top box took help first Mike gave us the zemax numbers then Dave O put them in oslo and in a 3d drawing .That my CNC water jet could make a file . Any mistake it would be hard to find . My goal was make everything on the top correct and not move it ever . Mike used the real numbers off my finished optics for the final distances and tilt and de center info. Dave O putting it in OSLO was great as it proved the first numbers were good . Having a working 20 f8 chief for 3.5 years I was sure the design would be easy to setup and it is . When you have a working one no one can tell me they do not work .The 17 Wide Band CHief is not much different than the 20 that ED designed . Only the corrector and secondary is fixed . EDs way of setting the mirrors is very powerfull and why the chief works .Be great if ED Mike or Dave would explain the design

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Dave O
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Reged: 12/21/11

Loc: Sri Lanka
Re: 17 inch spotplots new [Re: kfrederick]
      #5534421 - 11/22/12 08:30 PM

lol -- I'll leave any 'explaining of the design' up to the Jones's and other optics experts ... I simply crunched numbers that were provided by Mike. Yes, verifying the numbers in OSLO was one way to help eliminate errors (and allow you and others to play with the design); but my OSLO skills are not sufficient to optimize this design to the level that Ed and Mike are capable of using ZEMAX.

Your idea of 'fixing' all the elements in the 'top box'; effectively reducing the number of variables to overcome in aligning the optics worked beyond my expectations ... putting it together and getting an image on the first go was a welcome surprise!

Looking forward to any further modifications in the mechanical portion of the design, as you continue to tweak it for optimal performance. Thanks for sharing.


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kfrederick
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Re: 17 inch spotplots new [Re: Dave O]
      #5534452 - 11/22/12 08:50 PM

Dave your work was great .With out it I would have failed . I owe you and Mike . Thanks

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5535016 - 11/23/12 08:38 AM

Took a risk as none of the optics had any value except for this CHief and if one mistake came up I would have little chance to find it out . So it was all or nothing .Sure glad it was all good .

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kfrederick
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Re: 17 inch spotplots new [Re: kfrederick]
      #5539866 - 11/26/12 07:00 AM

Jupiter last night was very clear, in the 17 inch offaxis setup took 5 min It has the depth of focus of a f9 newt . Very happy with it .

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