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Oh, why not? Another Rosin, for Ed Turco

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#1 Mike I. Jones

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Posted 04 December 2012 - 06:38 PM

Ed Turco IM'd me with an interest to build a 12" f/6. Knowing Ed, it's worth the time to design him something, because he'll actually go and build it!

Estimating that a standard 12.5" blank with a chamfered edge can have about 12.4" clear aperture, here's a really nice f/6 system for Ed and everyone. No cemented doublets, just a pair of single meniscus lenses in a cell with an airspace ring, and a practical, shallow hyperboloid primary only 17.7% deeper than the equivalent paraboloid. This is unusually nice and shallow; most Rosin primaries want to be in the 200% correction range.

The N-PSK3 and fused silica glass blanks should be readily available in H3-H4 quality. 3" BFL should be plenty for CCD/filter cameras as well as DSLR's like the 60Da. Axial imagery is sharp enough for high-power visual work, the field is within a few percent of DL over a 1" diameter, and the corrected spectral band is from 0.4-0.9 microns, suitable for any CCD's and DSLR's without giving image bloat. The diagonal is a standard 3.0" minor axis, with a lateral offset of 0.106" away from the focuser and toward the primary.

Mike

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#2 Mike I. Jones

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Posted 04 December 2012 - 06:41 PM

Here's the layout drawing.

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#3 Mike I. Jones

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Posted 04 December 2012 - 06:43 PM

And here are the spots over the 1" diameter field, from 0.4-0.9um. It's a nice sharp scope for visual and astrographic use.
Mike

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#4 dan_h

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Posted 04 December 2012 - 06:50 PM

Those are nice spots. Would this scale down to 8" size or even 10"?

dan

#5 Mike I. Jones

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Posted 04 December 2012 - 07:12 PM

Quite nicely, if the FOV diameter scales down as well. The design and diagonal size would have to be tweaked for 8" and 10" designs to maintain the 1" diameter FOV, if that's important. I briefly looked around in OSLO-EDU and can't find how to scale a system. Anybody know?
Mike

#6 MKV

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Posted 04 December 2012 - 08:09 PM

I briefly looked around in OSLO-EDU and can't find how to scale a system. Anybody know?
Mike

On the left, right click on the AST surface tab (or any other surface tab) and the program will open a Scale function. Click on it and choose between the two options.

Mladen

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#7 Mike I. Jones

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Posted 04 December 2012 - 08:26 PM

Cool - thanks! Now where's the button that lets you have more than 10 surfaces? :)

#8 ed_turco

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Posted 05 December 2012 - 09:24 AM

Gee Mike,

Thanks! There is a PM for you.


Ed Turco

#9 MKV

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Posted 05 December 2012 - 11:42 AM

Cool - thanks! Now where's the button that lets you have more than 10 surfaces? :)

That will cost you! :) Originally, OSLO 5.4 LT could handle up to 12 surfaces, and had many of the functions that are now restricted to non-free versions. Unfortunately, v. 5.4 also lacks many of the new features available in Oslo.edu and has a very limited glass catalog.

You get what you pay for. Buy, hey, OSLO is a lot kinder to amateurs than any other company by providing a fairly sophisticated optical program for free. I don't think they are losing any revenue this way. I wish Zemax had a their own version of Oslo.edu. Their free version doesn't even come close.

Mladen

#10 Gordon Rayner

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Posted 07 December 2012 - 02:59 AM

One of the original developers of OSLO, a former(?) Univ. of Rochester (NY) faculty member at their Institute of Optics , led me by the hand , at a booth at a SPIE convention a few years ago, to consider:
A system with more than the number of surfaces allowed in the student version, could be analyzed or synthesized in two or more stages:

Work to the capacity of the student version. Use its output as the input for further work ,"downstream" with the student version . Would this be on a different computer? Could it be used as input to the ZEMAX student version?

I have no experience with that technique, nor any experience with OSLO, ZEMAX, or any other lens design program. I have read Bruce Walker's SPIE Press book: Fundamentals of Optical Design, second edition. He uses OSLO there. ( What is the program used at www.AlbrechtKoehler.de in the binoculars section ( English language headings in the aberration plots, for some reason. Google's translator only worked once on that site. ))

I used Walker's mirror flatness tolerancing method, in the first and second editions, in evaluating the requirements for 2-flat mirror phantom roof pseudo Amici "prisms" for binocular telescopes . I programmed an hp-48 for mirror adaptation of the WW II Zeiss unilateral IPD change arrangement in their 25 x 100 and 12 x 60 , both with 60 deg deviation of the sight line . The 3D compound angle situation in the mirror "prism" is best approached with vectors .

I built a preliminary model with plexiglass second surface bathroom mirror stock. The mirror system deviation of the line of sight can be perhaps 70 deg, up to and including 180 deg, but once chosen, it is fixed, not variable .

Matsumoto-san uses a different IPD arrangement, and chose 90 deg. deviation in his EMS products.

#11 Mike I. Jones

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Posted 09 December 2012 - 11:47 PM

Ed PM'd and said he had some 54mm BK1 and F4 blanks, and a 12.5" primary chamfered down to 12" aperture, with a 75" EFL and 10% overcorrection (giving a conic constant of -1.1). With those values, I came up with this system for him, which came out sharp enough for good astrophotography and visual use. I tried F4/BK1 and BK1/F4, and the F4/BK1 worked out the best. The BFL is 3" to give plenty of room for DSLR and CCD/filter cameras as well as visual use. The field is 1.1" diameter, and color corrected over the 0.41-0.85um spectral band.

Mike

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#12 Mike I. Jones

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Posted 09 December 2012 - 11:57 PM

Here are the spots. They're serviceable, but could be sharper if Ed wanted to figure his primary to about 22% overcorrection and the lenses were re-optimized. But, he said he just wants to use the primary as is.

Mike

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#13 Mike I. Jones

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Posted 09 December 2012 - 11:58 PM

and here's the OSLO-EDU file for it. Ed - do these lens elements look do-able for you?
Mike

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#14 Mark Harry

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Posted 10 December 2012 - 07:16 AM

I tickled the focus, and conic of that mirror. Wow, pretty nice!
Knew we kept you around for sumpthin'!
M.

#15 ed_turco

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Posted 10 December 2012 - 08:45 AM

Oh thank you Mike!!! Could I have a drawing? PM sent. The images look fabulous!!

#16 Mike I. Jones

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Posted 10 December 2012 - 09:04 AM

Sure. And if Dr. Harry would be interested, like I said, if your primary were figured to -1.22, or 22% deeper than the equivalent paraboloid, the spots get a lot better. I'll email you details on Yahoo.
Mike






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