32 replies to this topic

[psionik]

I came across the Newtonian Telescope Designer by Mel Bartels and it is a fantastic tool.

 

I was wondering if there was anything like this somewhere for a Maksutov - Newtonian?  Or even just some resources (books, software) on designing one with specifics on curvature of the corrector and mirror combination.

 

I love the idea of spherical surfaces, since they are so easy to get right relative to other shapes.

 

 

[luxo II]

https://www.telescop.../Mak-camera.htm

 

The secondary flat has no effect (it's flat).

 

Let me guess, I don't suppose you've bought a set of 10" f/6 optics ?

Edited by luxo II, 06 December 2022 - 01:01 AM.

[ccaissie]

The ATMT-Optics series by Mackintosh has extensive Mak design data...more for the optical design than the OTA build.

 

https://www.research...ksutov_Circular

 

I have a 6"f6 Mak Newt originally made with Russian optics in a scope by Orion, called the Argonaut.  Beautiful optics, excellent views, as good as our 6" Jaegers scopes, and more compact.    I remember a club member having the Ceravolo 6" f/6 Mak Newt. He kicks himself for selling it.

[MKV]

An f/6 Maksutov of that size can be designed to perform exquisitely even without any aspheric surfaces. 

[psionik]

https://www.telescop.../Mak-camera.htm

 

The secondary flat has no effect (it's flat).

 

Let me guess, I don't suppose you've bought a set of 10" f/6 optics ?

 

I don't have optics specifically for that, but over the last couple of years I've gathered enough parts and pieces to make several scopes from 8" to 20" of either newtonian or mak-newt design.

 

The link you posted seems to be dead, by the way.

[luxo II]

The link you posted seems to be dead, by the way.

Definitely works here. You can google it for yourself "telescope optics.net" will find it. Note however that the analytical solution is only a starting point, the final design has to be optimised by raytracing (eg OSLO). 

 

There are other resources too, including:

 

- Sky & Telescope Gleanings Bulletin C contains Maksutovs original paper, with the maths (see page attached).

 

 

- https://www.cfht.haw.../Maksutov.html;

 

You may find this one interesting too 

https://home.strw.le..._Telescopes.pdf

Attached Thumbnails

• 

Edited by luxo II, 07 December 2022 - 06:08 PM.

[davidc135]

Vla Sacek in 'Telescope-Optics.net', mentioned above, has some cautionary words about making Maksutovs, in particular, very tight tolerances. Plus the expense of the meniscus blank. Page 10.2.3.2

 

You mention that you have an accumulation of glass etc and so if you have ATM experience and the meniscus blank it would be worthwhile, and also fun to follow. Otherwise an f6 Newt would be miles simpler and easier, even if it's a paraboloid.

 

David

[MKV]

[psionik]

You mention that you have an accumulation of glass etc and so if you have ATM experience and the meniscus blank it would be worthwhile, and also fun to follow. Otherwise an f6 Newt would be miles simpler and easier, even if it's a paraboloid.

 

David

I have between 2 and 6 pieces each of 8" 10" 12" 16" and 20" and one each of 14" and 18" and they are between 3/4" and 3" thick.  A few are plate glass, some pyrex or similar, several fused silica.  I also have maybe 10 scopes, some I made from scratch and some I purchased for parts later.  I've ground polished and coated at least half a dozen mirror sets so far over the years.

 

The very first scope I made was a 6" F8.  As I recall I chose those specs because at F8 the difference between a sphere and parabola was small enough that I could skip parabolization and still get good results.  I polished that glass for so long and tested it so many times that I think most people would say it was unnecessarily obsessive, but in the end I had an extremely smooth surface without any discernible blemishes at all.  This scope ended up giving me some of the clearest views even considering some 8" and 10" ones I built later.  I eventually sold it to a friend for way less than it was worth, and regret it since the only small scopes I have now are mak-cass and although they are conveniently small, they do not give the same impression of clarity I had with my first.

Edited by psionik, 08 December 2022 - 01:10 PM.

[davidc135]

I have between 2 and 6 pieces each of 8" 10" 12" 16" and 20" and one each of 14" and 18" and they are between 3/4" and 3" thick.  A few are plate glass, some pyrex or similar, several fused silica.  I also have maybe 10 scopes, some I made from scratch and some I purchased for parts later.  I've ground polished and coated at least half a dozen mirror sets so far over the years.

 

The very first scope I made was a 6" F8.  As I recall I chose those specs because at F8 the difference between a sphere and parabola was small enough that I could skip parabolization and still get good results.  I polished that glass for so long and tested it so many times that I think most people would say it was unnecessarily obsessive, but in the end I had an extremely smooth surface without any discernible blemishes at all.  This scope ended up giving me some of the clearest views even considering some 8" and 10" ones I built later.  I eventually sold it to a friend for way less than it was worth, and regret it since the only small scopes I have now are mak-cass and although they are conveniently small, they do not give the same impression of clarity I had with my first.

That certainly ticks the experience box! It would be great to follow your progress if you decide to go ahead.

 

David

[DAVIDG]

 There is a  bit more to making a Mak corrector vs a mirror.  First you need to  know the refractive index of the glass and that it is optical grade since that will determine the parameters of the corrector.   The radius and thickness are critical on Mak  correctors  since both control spherical aberration and color correction. They have tight tolerances so your going to need a good spherometer and  a flat to  zero it on, thickness gauge and wedge tester. As you grind you need to keep both curves optically concentric, hit the radius on their values while also hitting the thickness correctly.  So what ever design you come up with you need to determine the tolerances on  the all the surfaces  and be able to be within all of them since they add.

 

             - Dave 

Edited by DAVIDG, 08 December 2022 - 03:55 PM.

[davidc135]

Psionik.

 

Do you have a Mak-Newt aperture and f ratio in mind?

 

Does anyone remember the ATM who began a Mak thread some while ago? I don't know if he finished it but the cost of the smallish corrector blank was $300, IIRC. He wanted to grind both surfaces by hand but it seemed a marathon trudge best avoided by getting them curve generated, or doing it oneself, which isn't too hard if there's a bench drill.

 

David

 

PS Corrections in post 14 below

Edited by davidc135, 08 December 2022 - 06:32 PM.

[luxo II]

Probably DJNoecker in the first of these threads, but there are others, whether any were finished successfully I don't know...

 

https://www.cloudyni...ksutov-project/

https://www.cloudyni...utov-corrector/

 

https://www.cloudyni...ing-a-maksutov/

https://www.cloudyni...aksutov-optics/

https://www.cloudyni...aking-maksutov/

Edited by luxo II, 08 December 2022 - 06:01 PM.

[davidc135]

Probably DJNoecker in the first of these threads, but there are others, whether any were finished successfully I don't know...

 

https://www.cloudyni...ksutov-project/

https://www.cloudyni...utov-corrector/

 

https://www.cloudyni...ing-a-maksutov/

https://www.cloudyni...aksutov-optics/

https://www.cloudyni...aking-maksutov/

Yes, it was Dan Noecker's 'Maksutov project' I was thinking about. The clear aperture (7.5'') was greater than I remember and the cost around $500 shipped for probably an 8'' blank.

 

David

[ccaissie]

Stan Brower gave one of our club members a molded Mak corrector blank.  It's such a deep figure that the Maksutov Club got together and ordered a bunch of molded blanks.  When I acquired the pile of goods, I hoped the blank was in there, but he must have traded it.

 

There might be few around still.  BSC-2 glass 11"  diameter, and about an inch thick I remember.  Was the corrector for a 12.5" design.

 

I posted the link to the downloadable ATMT .pdf which is the compiled circulars of the Mak Club.  That should be your bible Re: making a Mak. You might also benefit from the Volume 2: Mechanical.

 

Again:

 

https://www.research...ksutov_Circular

[psionik]

 There is a  bit more to making a Mak corrector vs a mirror.  First you need to  know the refractive index of the glass and that it is optical grade since that will determine the parameters of the corrector.   The radius and thickness are critical on Mak  correctors  since both control spherical aberration and color correction. They have tight tolerances so your going to need a good spherometer and  a flat to  zero it on, thickness gauge and wedge tester. As you grind you need to keep both curves optically concentric, hit the radius on their values while also hitting the thickness correctly.  So what ever design you come up with you need to determine the tolerances on  the all the surfaces  and be able to be within all of them since they add.

 

             - Dave 

 

You say they add but I'll bet it's rather worse than that - I suspect at each stage imperfections multiply.  So precision and accuracy are the name of the game for sure.  And yep I'm looking into some test apparatus to verify the IOR precisely.

 

Also, considering how useful and almost necessary it will be for the work I intend on doing, I'm seriously looking into some commercial flats for testing.  I'm justifying the expense (I've spent less on entire scopes) with the argument that when I'm done with them I can sell them later.  I thought about making my own flats for months but the effort would just slow me down getting to what I'm really looking forward to.  I think the hard part will be finding a buyer but I guess we'll see...

 

Also picking up a few more pieces from Edmund I anticipate using.

 

I'm also not sure what optics software I might use to supplement my design efforts.  What I've looked at so far seems to have rather steep learning curves for the uninitiated.  Bite >> chew.

 

In the immortal words of Jim Carey:

 

"Somebuddeh stop meh!"

Edited by psionik, 08 December 2022 - 07:04 PM.

[zernikepolynomial]

If I really wanted to make a maksutov based design, I would do lots of different calculations based on ray tracing optics and wave optics. So I would use a ray trace simulator or something that works with ray transfer matrices, and I would do some numerical calculations based on Fresnel-Kirchoff diffraction. 

 

For the wave optics stuff, you can use python and numerical libraries for solving stuff. For ray tracing, there are many simulations out there. Nvidia has one called OptiX and that allows you to simulate rays. I do believe you need to be careful with refraction indices, as they are a function of wavelength, and glass has a refraction index. 

[psionik]

If I really wanted to make a maksutov based design, I would do lots of different calculations based on ray tracing optics and wave optics. So I would use a ray trace simulator or something that works with ray transfer matrices, and I would do some numerical calculations based on Fresnel-Kirchoff diffraction. 

 

For the wave optics stuff, you can use python and numerical libraries for solving stuff. For ray tracing, there are many simulations out there. Nvidia has one called OptiX and that allows you to simulate rays. I do believe you need to be careful with refraction indices, as they are a function of wavelength, and glass has a refraction index. 

 

Every time I hear the phrase "ray tracing" my mind goes back to my 2nd hobby - which is 3D imagery via http://www.povray.org/

 

This is a software program I first got started in via a mailed floppy disk from a share-ware library in 1991.

 

I have programmed it to simulate caustics and diffraction using photons, ior values, and different wavelengths of light sources, and because of my experience with it I am itching to give it a try with simulating telescope optics.  I'm 47 but I can definitely feel that "old dog new tricks" stubbornness when considering learning a whole new field and computer program.  I imagine it was the same for those engineers who learned how to use a slide rule and then one day pocket calculators came out that could do logarithms.  I watched my poor old mom insist on using pencil and paper once when she had a calculator on her desk...

 

That OSLO program looks like it would fit the bill but I will definitely look into OptiX as well.  Any other suggestions?

Edited by psionik, 08 December 2022 - 07:24 PM.

[starcanoe]

Any reason it's gotta be a Mak Newt?

 

My impression is that a Lourie Houghton (spelling) is much less demanding tolerance wise. And while you have two lenses...they are modest in their curvature unlike a "deep dish" mak lens.

[psionik]

Any reason it's gotta be a Mak Newt?

 

My impression is that a Lourie Houghton (spelling) is much less demanding tolerance wise. And while you have two lenses...they are modest in their curvature unlike a "deep dish" mak lens.

 

I like the faster f ratios as compared to schmitt-cass and mak-cass, but I want refractor-like photoimagery, but I don't want the astronomical cost of refractors 8" and above.

 

I don't know what a Lourie Houghton design is (first time I've heard of it) but I'm about to look it up...

 

I am building a large CNC lathe which I intend on using diamond tools to hog out my mak corrector with.  I believe this will expedite the process and leave me with good starting geometry before I start polishing it down.

[zernikepolynomial]

And for Kirchoff-Fresnel diffraction, I would do it piecewise over the propagation axis. I would go layer by layer through strongly curved optical components, each time recalculating complex amplitude of the field. So the meniscus would need multiple wave calculations, much like how the integral transform for a thick converging lens is calculated. In this case, you are solving a THICC negative meniscus with a holed cylinder boundary condition, an air gap propagation with cylindrical boundary conditions, a primary mirror, another airgap propagation, and then a secondary mirror, and then airgap propagation through a focuser hole to the final image plane. And you will need to run this calculation, with whatever software you do it in, for different angles of plane waves to get off-axis deviation calculations. 

 

For the ray tracing stuff, you can use reflection and transmission coefficients to calculate light loss. 

 

If you are going to just DIY this for yourself, then its no big deal to make more approximations and just use simplified designs from other people, but if you want to do this commercially, I would go the extra mile and give very precise results for the image plane. There are other ways that people have used before computers, but based on my own knowledge with todays technology, this is what I would do if I were to embark on a commercial enterprise selling maksutov-newtonians. I would model everything as precisely as possible. 

[luxo II]

I like the faster f ratios as compared to schmitt-cass and mak-cass, but I want refractor-like photoimagery, but I don't want the astronomical cost of refractors 8" and above.

It's an interesting view. Focal ratio really drives the choice of solution, IMHO:

 

SCT with Hyperstar = f/1.9 or f/2 (Celestron + Starizona)

Baker-Schmidt = f/2... f/3 (Ottiche Zen),

Takahashi Epsilon 180 = f/2.8,

Sharpstar 150 Astrograph = f/2.8,

RASA = f/3.3 (Celestron),

Flatfield Maksutov Camera = f/3.7 (Ottiche Zen)

Newtonian+Starizona Nexus = f/3...f/6 (any newtonian + Starizona Nexus corrector/reducer),

Newtonians + Paracorr = f/4 ... f/6 (any newtonian + Televue Paracorr),

Maksutov-Newtonians = f/4.8 or f/5.3 (David Levy Comet Hunter or Skywatcher MN190),

Maksutov-Newtonians = f/4 to f/8 -  Russian ones - secondhand only and very rare;

Schmidt Newtonians = f/4 - Meade, secondhand only and very rare.

 

While a mak-newtonian looks attractive for something around f/4-f/6 I'd have to say these days it doesn't make a lot of sense when you could take any normal newtonian and add the Starizon Nexus, or a Paracorr.

 

If determined to do a DIY scope I'd probably buy the glass from Ottiche Zen and assemble my own tube.

Edited by luxo II, 08 December 2022 - 09:01 PM.

[zernikepolynomial]

It's an interesting view. Focal ratio really drives the choice of solution, IMHO:

 

SCT with Hyperstar = f/1.9 or f/2 (Celestron + Starizona)

Baker-Schmidt = f/2... f/3 (Ottiche Zen),

Takahashi Epsilon 180 = f/2.8,

Sharpstar 150 Astrograph = f/2.8,

RASA = f/3.3 (Celestron),

Flatfield Maksutov Camera = f/3.7 (Ottiche Zen)

Newtonian+Starizona Nexus = f/3...f/6 (any newtonian + Starizona Nexus corrector/reducer),

Newtonians + Paracorr = f/4 ... f/6 (any newtonian + Televue Paracorr),

Maksutov-Newtonians = f/4.8 or f/5.3 (David Levy Comet Hunter or Skywatcher MN190),

Maksutov-Newtonians = f/4 to f/8 -  Russian ones - secondhand only and very rare;

Schmidt Newtonians = f/4 - Meade, secondhand only and very rare.

 

While a mak-newtonian looks attractive for something around f/4-f/6 I'd have to say these days it doesn't make a lot of sense when you could take any normal newtonian and add the Starizon Nexus, or a Paracorr.

 

If determined to do a DIY scope I'd probably buy the glass from Ottiche Zen and assemble my own tube.

 

When it comes to the starizona nexus, you need to be really careful with your diagonal to focus plane distance. The central obstruction requirement becomes problematic for certain sized scopes, and it will result in uneven illumination. Can you work around this? Sure, but its not really what you want. Believe it or not, the 6" f/4 works better with a starizona nexus when you use a 62.5 - 66mm secondary with a diagonal to focal plane distance of 215mm and your chip is constrained to a 16mm hypotenuse (equivalent to a 21mm chip at native f/4). To get relatively even illumination with a 8" f/4 and a starizona nexus is actually more difficult and CO's approaching 50% are required for it. Meanwhile, the 6" f/4 can get away with a CO of about 43% and have more even illumination with the nexus. The chip size is constrained by both the secondary size (and thus the width of even illumination) and the fact the nexus is 80mm long, and at 215mm diagonal to focal plane distance, must stick down into the tube. Really wide rays will be modified by the nexus blocking the light. 

[davidc135]

I like the faster f ratios as compared to schmitt-cass and mak-cass, but I want refractor-like photoimagery, but I don't want the astronomical cost of refractors 8" and above.

 

I don't know what a Lourie Houghton design is (first time I've heard of it) but I'm about to look it up...

 

I am building a large CNC lathe which I intend on using diamond tools to hog out my mak corrector with.  I believe this will expedite the process and leave me with good starting geometry before I start polishing it down.

This suggests that you have something like an 8'' f6 in mind. As Luxo says you've got to wonder if the Newt isn't as good a solution as any. With a 20% diagonal for planetary and a larger one plus coma corrector for wider field photography.

 

Whether the plain Newt is chosen or one of the Cat versions- Schmidt, Mak or (Lurie)Houghton it's manufacturing standards that count for most.

 

Each of these correctors only has to correct for 0.83 waves SA so basic design might suffice for the Mak. Good to check though.

 

Off axis imagery improves from a basic Newt to Schmidt to Mak with the optimised Houghton/Newt +CC being just about perfect.

 

'Telescope-Optics.net compares these alternatives. The Newt could be given a window to avoid spider diffraction effects.

 

David

Edited by davidc135, 09 December 2022 - 08:36 AM.

[luxo II]

When it comes to the starizona nexus...

I'm well aware of the issues with it. Collimation is likewise challenging.

Edited by luxo II, 09 December 2022 - 06:47 AM.