Mark Harry
Vendor
Reged: 09/05/05
Loc: Northeast USA
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Re: An interesting Mak Newt design
[Re: MKV]
#5100583 - 03/02/12 07:47 AM
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One thing I can say about obstruction. I've had several scopes where obstruction is around 30-33%. To my eyes, I see a significant increase in contrast loss and scatter. It's objectionable. I find myself wanting better.
However, when down in the 20 percentiles, it's not so bad; you might say it's tolerable. I think I would like the overall design with the 1.83" rather than the larger diagonal. 0.4-0.5" fully illuminated on a fast scope is plenty adequate, ime.
(I hope we can keep discussing the MN design---?)
Thanks,
Mark
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Benach
Pooh-Bah
Reged: 01/24/08
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Re: An interesting Mak Newt design
[Re: MKV]
#5100591 - 03/02/12 07:59 AM
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Yup, it is indeed a redundancy. And in fact, to make Dutch weirder: Dutch ATMers usually say that they're making a parabola indeed.
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: An interesting Mak Newt design
[Re: Mark Harry]
#5100610 - 03/02/12 08:20 AM Attachment (20 downloads)
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I think regardless, if compared to a very fast refractor, or practically any other scope, a Mak Newt does pretty darn well at delivering the goods; wouldn't you agree?
That goes without saying, Mark. As to the slight differences, again, I am a designer but I am also an ATM, with the emphasis on the "M", a maker, and making something that's on paper come alive is by far a lot more challenging these days that coming up with an optimized theoretical design.
Real-world telescope users know that these academic differences are often just that - academic niceties which may not be discernable under actual observing conditions. Nevertheless we can learn a lot from them.
As for placing a Schmidt-like deformation on it, the only way I am aware of is by selectively removing proportional areas of glass which is accomplished with specially shaped polishing laps and not by differential strokes.
For comparison, I include spread function images of each solution, as is. They can only be compared by their results because they were designed and optimized under different conditions. Mike's configuration provides the smallest image but they all hover around 4 microns, as expected. I really don;t think this would constitute a discernable difference, but in theory it's there.
Mladen
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Loc: Fort Worth TX
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Re: An interesting Mak Newt design
[Re: MKV]
#5100682 - 03/02/12 09:34 AM
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Three points:
1. The R1 asphere doesn't involve any Schmidt-plate like flexing, vacuum, etc. It just involves removing a few millionths of an inch of glass from the intermediate zones. The deformation from spherical is hundreds to thousands of times smaller than that for almost any range of Schmidt correctors.
2. The asphere is at the aperture stop of the system, on R1, where it does the most good over the whole field. If the FOV was wider, there would be a greater difference in the optimized spots at the edge of the field in aspherizing either R1 or the primary. At the very narrow field of this design, you're right, it's a wash whether to aspherize R1 or the primary.
3. I didn't aspherize to make the spots smaller, I aspherized to help bring g-line into focus with F,d, and C. I don't hate many things, but I hate blue/violet flare around star images if there is an easy fix like this.
Wish I could do the same for Jim Egger's big refractor, but the only ways are either to get a Chromacor, if those are still around, or to use glass that costs 50-100X higher than his BK7/F2 glass.
Mike
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Benach
Pooh-Bah
Reged: 01/24/08
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Re: An interesting Mak Newt design
[Re: Mike I. Jones]
#5100694 - 03/02/12 09:41 AM
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Mike: Chromacorrs are only available second hand and are highly demanded.
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: An interesting Mak Newt design
[Re: Mike I. Jones]
#5100812 - 03/02/12 10:47 AM
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The R1 asphere doesn't involve any Schmidt-plate like flexing, vacuum, etc. It just involves removing a few millionths of an inch of glass from the intermediate zones. The deformation from spherical is hundreds to thousands of times smaller than that for almost any range of Schmidt correctors.
Mike, I never suggested the aspheric correction in this case would be anything in magnitude comparable to a Schmidt plate. However seemingly minute, the selective removal of glass is still very exacting and critical.
From a shop technique point of view, what happens if you remove too much? You can't just switch the tool and the mirror and "work" your way back, as is possible with conic section solids. If I can get a comparable correction by aspherizing the primary with a conic, I will choose the conic precisely for that reason.
Your point about wider field coverage is true, but in this case the image filed is only one degree and, as you noted, is a difference without a distinction.
Finally, how much of a blue halo would be present in Mark's original design, i.e. without the R1 deformation, as compared to that of refractors?
I think the easiest way for Mark to avoid any halo with all spherical surfaces is to make a Busack/Honders-Riccardi type medial Newtonian. If he can make a meniscus to Mak's tolerances, he should be able to make a Mangin primary.
Mladen
Edited by MKV (03/02/12 11:03 AM)
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Mark Harry
Vendor
Reged: 09/05/05
Loc: Northeast USA
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Re: An interesting Mak Newt design
[Re: MKV]
#5100997 - 03/02/12 12:37 PM
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I agree with Mike- don't see much difference between the designs based on 3 colors. But with placing the G line smack on top of the others, and halving the total range of errors (approx) I think it's worth it.
It'll be easy to find out what a purple halo would look like. pretty easy to add another wavelength and take a look-
M.
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: An interesting Mak Newt design
[Re: Mark Harry]
#5101665 - 03/02/12 07:17 PM
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I agree with Mike- don't see much difference between the designs based on 3 colors. But with placing the G line smack on top of the others, and halving the total range of errors (approx) I think it's worth it.
It'll be easy to find out what a purple halo would look like. pretty easy to add another wavelength and take a look-
M.
Mark, you can add Hg or Aragon lines to Mike's design and you will have the same clean apochromatic image across the whole range, with all the light neatly tucked into an Airy disc. Pretty amazing! Clearly, Mike's configuration is superior. No one is disputing that.
I am curious how much, if any halo would be visible in your original design or in my version of it. You don't hear many people complain of residual chromatic aberration in Mak Newts, but then most of them are not f/3.5 either!
My concern is not so much creating a telescope on paper, but making one. And when it comes to "touching up" a lens, by removing small amounts of glass in precisely located sections of an aperture, and in a precisely limited area, I am not sure it's an easy task, especially because once you remove too much you can't just go back by reversing the process.
And how many times did you overcorrect? I can think of quite a few times in my case. I guess it's just me. I love optical design but I also love making optics and I know the pitfalls I encounter making them. That's all.
I guess the trick is to make a lap that resembles the desired surface profile, work a few strokes and retest often. Once mastered, the method offers many possibilities. Now I am curious to find out how difficult that might be. I can see a new project coming... 
Mladen
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Loren Chang
member
Reged: 04/28/09
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Re: An interesting Mak Newt design
[Re: Mark Harry]
#5102318 - 03/03/12 08:49 AM Attachment (16 downloads)
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I tried to add a diagonal to Mark's design in OSLO. It turns out size of diagonal is 2.8"!
CLO and CAO wiil be 40% and 16% which is different from Mark. Do I miss anything again?
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Loren Chang
member
Reged: 04/28/09
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Re: An interesting Mak Newt design
[Re: Loren Chang]
#5102320 - 03/03/12 08:51 AM Attachment (34 downloads)
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Here is OSLO file.
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Mark Harry
Vendor
Reged: 09/05/05
Loc: Northeast USA
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Re: An interesting Mak Newt design
[Re: Loren Chang]
#5102735 - 03/03/12 01:05 PM
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Alright...
I chose a 1.83' diagonal to fully illuminate a 1 degree field; totally adequate at F/3.88. It's all I feel is necessary. If I chose to use a diag of the size you mention, if you look at the primary mirror, the required ap is close to 9" (!!!) While it's necessary for 100% illumination by the numbers, I generally choose around .4-.500" and it's proven to be totally adequate for visual which is prinarily how I'll use it. So if I lose a little aperture with a 24 Pan...? @ F.3.8~ I'm not too concerned. The falloff of illumination would be gradual anyhow...
Mladen,
I looked at my all-spherical, and the violet halo blew the plots to about double the size of Rho. Mike's placed it right in the same RGB group. I haven't heard of complaints either. but if it's only going to take a few extra minutes, what the heck.
As for making a "petal 'lap'" and screwing around with depressing a zone, no; short answer. Many here will tell you that it's the way, but I don't accept that. I have a pretty good idea how I produced one of these curves with a 3/4 size polisher. But that same Many haven't polished the quantity of glass I have, either. If the method you mention was used in an optical shop, you'd have gotten a pink slip and a last check with a kind patronizing look while showing you to the door!
1/4 wave deformation can be aquired in as little as 5 minutes of polishing time. The thing to do to prevent overshoot, is to work it a couple minutes, and then test. In a previous conversation, Mike said to simply take the scope and rework R1 with an AC flat. As a sphere, the .707 zone should read as being high. A few minutes work should show a significant and measurable delta. Then proceed to finish it up.
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: An interesting Mak Newt design
[Re: Mark Harry]
#5102952 - 03/03/12 03:05 PM Attachment (29 downloads)
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Mark, it's good to know someone who has actually done this. Maybe you should write an article for all to learn this technique. A few pictures, null tests, etc. wouldn't hurt either.
Just curious: why not make a Honders-Riccardi, such as the one below, instead of a MN? No aspherics, 3.4 degree field (!), and one that can tolerate all the blue and violet you can throw at it!
Mladen
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: An interesting Mak Newt design
[Re: Mark Harry]
#5103200 - 03/03/12 05:49 PM Attachment (20 downloads)
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Alright...
I chose a 1.83' diagonal to fully illuminate a 1 degree field; totally adequate at F/3.88.
Mark, Loren's file shows the diagonal needed is a whole inch bigger. The digonal of your choice is just about 50% of the one required for full illuination. But, 2.8 inches (40% linear diameter of the aperture), as Loren suggests, image degradation would be severe. Makes me wonder, why go through all the trouble optically correcting for blue and violet and letting the rest go?
Mladen
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kfrederick
Carpal Tunnel
Reged: 02/01/08
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Re: An interesting Mak Newt design
[Re: MKV]
#5103274 - 03/03/12 06:28 PM
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How much harder would a HAMILTONIAN-YOLO optical system be to make??It is Unobstructed Mike /ED /Dave??
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alancygnusx2
professor emeritus
Reged: 11/25/08
Loc: CA
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Re: An interesting Mak Newt design
[Re: Mark Harry]
#5103365 - 03/03/12 07:23 PM
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Hi Mark,
You commented earlier that this mak-newt design will be better corrected than equivalent aperture and focal ratio newt, which i believe, but was curious to know by how much.
Here are the graphs for the type 2 paracorr:
Paracorr and focal ratios
The units are different on these graphs, than on your charts, how do you convert them to compare?
Alan
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Loren Chang
member
Reged: 04/28/09
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Re: An interesting Mak Newt design
[Re: MKV]
#5104000 - 03/04/12 05:45 AM
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2.8 inches (40% linear diameter of the aperture), as Loren suggests, image degradation would be severe. Makes me wonder, why go through all the trouble optically correcting for blue and violet and letting the rest go?
Hello Mlanden,
2.8" is for photography consideration since it's a F/4 instrument. 40% CLO was caculated from diagonal size. After I rechecked my OSLO file and considered only obstruction it created, 35% would be more appropriated. The violet color is out of focus a little but for photography purpose the image is acceptable at least.
Hello Mark,
I agree with you. Your setup is fine for visual. 
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MKV
Carpal Tunnel
Reged: 01/20/11
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Re: An interesting Mak Newt design
[Re: Loren Chang]
#5104048 - 03/04/12 07:04 AM Attachment (21 downloads)
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Thanks Loren. Mark is right as far as the CLO is concerned. Visually he can afford less than 100% illumination, and by choosing a smaller diagonal he will have cleaner images as shown below. Obviosuly, the Airy disc quality is better in the 20-25% CLO range.
As for the blue halo, I think we all agree that Mark's original configuration was not optimized and needed additional correction. In the case of his MN configuration, the color residual can be significantly reduced by aspherizing the primary, but a better correction is achieved by aspherizing R1 (Mike's congifuration).
I prefer the former because I know that if I overcorrect, I can bring a conic mirror back to sphere and then attempt correction again. I have no experience in removing selective areas of glass.
Unlike most of us, Mark does, and he seems confident that removing 1/4 wave of glass in select areas on R1 would take but 5 minutes in order to obtain Mike's superior correction.
Mladen
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Mark Harry
Vendor
Reged: 09/05/05
Loc: Northeast USA
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Re: An interesting Mak Newt design
[Re: MKV]
#5104072 - 03/04/12 07:40 AM
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Ah, interesting PSF images! 25% and below look pretty good.
M.
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Mark Harry
Vendor
Reged: 09/05/05
Loc: Northeast USA
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Re: An interesting Mak Newt design
[Re: alancygnusx2]
#5104088 - 03/04/12 07:52 AM
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I'd have to see a bit more than arbitrary graphs drawn by hand to substantiate their claim. Fairly crude, imo. I was also thinking of the paracorr 1, where the coma is reduced by a factor of 6.
But the right hand side showing a paraboloid alone, enough said. Coma dominates, plain and simple. But there's none in any of the MN designs that's visible in the plots. (much improved over paracorr 1)
Another thing to consider since the corrector of the MN is out there between the ROC and focus, there's no fiddling with the sub-aperture corrector collimation issues. The MN will for all intents, be just as simple as an equivalent Newt sans the Paracorr.
(did I mention the MN corrector is cheaper?)
M.
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Mark Harry
Vendor
Reged: 09/05/05
Loc: Northeast USA
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Re: An interesting Mak Newt design
[Re: Mark Harry]
#5104103 - 03/04/12 08:09 AM
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Mladen, I was thinking-
If working R1 with AC kicks the violet in line with the other 3 main RGB wavelengths, just how does that accomplish that trick? Since if working the mirror to an oblate is also even simpler it would not change the position of violet- but (as illustrated by the plots) reduce the plots of at least RGB significantly
Main thing, reworking the spherical mirror to a slight oblate does improve RGB, but doesn't accomplish the violet shift....
I wonder how else it could be done.
M.
Edited by Mark Harry (03/04/12 08:10 AM)
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