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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4938
Loc: MA
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I have access to Zemax and would like to get any interesting astro related models that individuals might have and be willing to send me. Specific models for SCTs MCTs, Schiefs, APOs, EPs etc would all be appreciated.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Well, here's a simple 8" f/10 SCT to get you started. I'll put up a few more when I have time.
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and others.
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Here's a 6" f/4 Mak-Newt to play with. It shows you how to define the elliptical diagonal aperture and offset central obstruction, and how to skip ray and surface drawing.
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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OK Luigi, here's a design up the complexity scale a little for you. This is a 4" f/10 apochromat, athermalized over the -5 to 40 deg. C range, over the 0.4-0.9 um spectrum and over a 1" diameter FOV. Do a Chromatic Focal Shift analysis; it's interesting as this is actually a double-S 4-color crossing curve. It's also a multi-configuration lens, so toggle between the temperatures using CTRL-A or SHIFT-CTRL-A. You can see the BFL change, but the spots stay nice and tight.
There are thousands of potential apochromat solutions, some with bad glass, some with less than bad glass. I paid no particular attention to the glass in this one, as it's just an example for you to experiment with.
One thing to keep in mind when designing these things is to use the RAID and RAED operands with the OPLT constraint to keep the incidence or exitance angles below about 20 degrees. Steep curves and high ray angles always equal nasty high-order aberrations and impossible tolerances on radii and thicknesses and a generally lousy lens to make and use.
Most folks use OSLO here rather than ZEMAX 'cause the price is right, but maybe Ed Jones can put up a couple of his Chief files as well. I'll do a few more soon.
Mike
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4938
Loc: MA
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Hi Mike, Thanks for those files, and the merit function tips. I'll have try playing with them this weekend. One thing that would be very useful for me is specific models of common photography lenses, like 50mm f/1.8 lenses, specifically the Nikkor AF, but others similar would be useful too. Do you know where I might find such models?
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Luigi,
Probably the best immediate source for photographic lenses would be Free Patents Online at http://www.freepatentsonline.com/. Optical patents nearly always include lens design prescriptions, as that's what is being patented. You'll have to hand-key them in, but that's good practice for you. I've hand-keyed in probably in the neighborhood of 4000-5000 lenses or more over the decades (it's an ongoing hobby, or maybe more like obsession). But rather than me just dumping files to you, you should key them in yourself for the learning experience. I can't tell you how to play a guitar either.
Good sources of lenses are the Warren J. Smith's books on optical design, G. H. Smith's book "Practical Computer-Aided Lens Design", Robert E. Fischer's excellent book "Optical System Design, Second Edition", all of Rudolf Kingslake's books, and Arthur Cox's book, "A System of Optical Design", which has over 300 lens prescriptions in the appendix. Very good recent books include "Telescope Optics" by Rutten and Venrooij, and the good books by Norm Remer and James Daley. There aren't very many lens designs in ATM 1-3, but it's interesting to key in some of James Baker's designs and optimize on them. Also go through back issues of Sky and Telescope and ATMJ, there are loads of designs in there.
Also go to your library and dig back through JOSA, Applied Optics and SPIE journals, as far back as you can go, and pick and choose designs to key in.
It's fun to take the old designs and see if, and usually how much, you can improve them. You can optimize a lens in seconds that took one of the old masters weeks or months to design, and often greatly improve the performance.
I've done all this and more, but like I said, collecting lens designs and optimizing them was and remains a serious lifetime hobby with me. I invite you to probe a ways into it. Using a good optics design tool like ZEMAX, I think you'd enjoy it. And after you key in three or four hundred lenses, and optimize half of them or so, you're going to be getting around on the big Z pretty well!
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and others.
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4938
Loc: MA
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Thanks for all the tips. I've had Smith's book for some time and need to crack it open again. Specifically though, I'm using the Nikkor camera lens in an application and it would be very useful to be able to have a model of it so I could characterize it's performance in these conditions. I'll try Nikon and see how far I get in getting the prescription.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Woo-eee! Good luck with that! Unless your exact lens prescription appears in a public patent, those designs, and especially the properties for any special-blend glasses used in it, would be as tightly held a secret at Nikkon as the formula for Coca-Cola!
Remember that you'll need the wavelength-dependent index, dispersion, dn/dt, CTE, etc. library data for all the glasses used as well as the basic prescription.
Maybe they would share it with you under an NDA, but that would still be amazing.
Good luck,
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and others.
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4938
Loc: MA
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I kinda doubt it. The number of them we would use would be absolutely miniscule in their scheme of things, certainly not enough to justify expending any effort on.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Hyped
newbie
Reged: 03/12/09
Posts: 2
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Mike,
I'm an optics guy for 15 years who only recently got into Astronomy (I know, shame on me!) Anyways, while I've modeled spectrometers in Zemax, I haven't done anything with telescope designs. I have an 8" Meade LX90 and was hoping to find more about the prescription for it. Has anyone sort of "figured out" the prescription for it or other popular commercial scopes? I'd like to "play" with it in Zemax to see what kind of (and how much) aberrations are instroduced with secondary mirror tilt ("miscollimation" apparently is the term used -- why is it called that when tilt on the secondary really doesn't affect collimation (from what I can infer) but would obviously introduce coma). Since the primary is a spherical mirror, I guess I'm interested in some "good guesses" on the prescription for the secondary mirror and the Schmidt corrector plate.
Any thoughts, suggestions, info appreciated!
Thanks,
Scott
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1306
Loc: Kiev, Ukraine
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Scott,
You should probably visit
http://www.telescope-optics.net/index.htm#TABLE_OF_CONTENTS
There are prescriptions for many telescopes, including commercially made SCT, ACX, SN, etc.
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Hyped
newbie
Reged: 03/12/09
Posts: 2
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Thanks Dennis. I'd been to that website recently, but never did hit that "Appendix" link! Nice!
Thanks again for pointing that out.
-Scott
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Hi Scott,
The only ways to get the exact prescription for the LX90 are:
1. If you're a trusted optical design employee at Meade,
2. Find the public patent for it if there is one, which would give the prescription, or
3. Take your LX90 apart and measure everything with a spherometer and interferometer to get the radii and asphericities, and measure all the spacings and thicknesses.
I have actually disassembled a Celestron and measured the 8" primary radius to be right at 32", with a very smooth sphere. Not knowing anything else to base it on, I used that value for this SCT guess.
Attached is a starting guess at an 8" f/10 SCT with an 8" BWD and spherical primary and secondary mirrors. I also put coordinate break surfaces on either side of the primary so you can independently tilt and decenter both mirrors.
Mike
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4938
Loc: MA
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Dennis,
Thanks for the tip on that website. I too have visited it a number of times and overlooked the Appenendix.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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