255 replies to this topic

[NHRob]

One of the grossest oversimplifications I've ever read ... (especially referring to a 4 inch F/15)

I agree.

 

By the argument of what "does the job"  everyone should just buy a cheap-a$$ 8" dob and be done with it.   It certainly will do the job.

[Redbetter]

I agree.

 

By the argument of what "does the job"  everyone should just buy a cheap-a$$ 8" dob and be done with it.   It certainly will do the job.

 

Now THAT is what I would call a gross oversimplification.  Oh the irony.

[NHRob]

I agree, thus my point

[AxelB]

Axel, triplet apos are born as photographic instruments.
Of course one can use them to do low-power wide-field observing -- there is no law against that --, but that it's like taking your Ferrari out of the garage to go to the grocery nearby and get some milk. You'd be better off with your bike.

To do wide-field observations, as you rightly say, you need first and foremost *excellent* quality eyepieces (PO41 or N31 come to mind).
As per telescope, you can just use a well-done short focus achromat.

Put your money into the eyepieces and get some *larger* short f/ratio achromat (and some narrowband filters).
OR -- even better -- a BIG pair of binoculars.

For low-pover visual, better invest in diameter (still remaining within quality) than in a triplet apo.

And, "super long refractors" are for hi-power planetary observing. Certainly not to frame M31, M42 or M45...!

That’s what I did, buying a 5" f6.5 AR127 ;-). Still, the stars are bloated compared to the view through an apo. It does the job and it’s nice for the price paid but you get what you pay for.

Edited by AxelB, 18 March 2018 - 11:40 AM.

[starcanoe]

A six inch F18 with a 50mm plossl would have nearly a one degree wide real FOV...plenty of deep sky objects where that is more than enough.

[dagadget]

Don't be so quick to judge, I have a triplet with the equivalent of FPL 51 glass and it is outstanding. You can see many sample photos by clicking in the Photo Gallery and searching AT130EDT to see some examples. There are also many examples of scopes that don't use FPL 53 glass that are outstanding from many manufacturers.

 

Before you focus on a glass type take some time to visit some star parties in your area and look through a various scopes, you may be very surprised at what you prefer.

I will second Roger's input on this. I also have an FPL-51 based triplet and it performs very well.  The other elements in the scope also control what the scope displays and a well engineered FPL-51 with the correct mating elements in the other glass can make the scope as good as any FPL-53 not as well engineered. Friday night the scope proved itself and was much better than a 127 mm FPL 53 scope... Had them side by side too...

[Richard Whalen]

I rarely ever think about the need for a wider fov visually using my 8" f15.5 and 31mm Nagler. And if I do I look through my 6" f12. Wide field imaging is another matter, but at the same time many fast scopes dont have enough image scale to frame most medium and small objects nicely or bring out detail unless they have a lot of aperture using todays large format cameras. I get that some like to scan at low powers and wide fields. But I like to scan at higher powers and smaller fov as you get increased contrast and can actually see things like small planetaries, small faint globulars, close doubles.

[Max Lattanzi]

Would a Littrow 6 inch F15 ED scope be workable? Doesn't a Littrow (or something where the the two internal radi are the same) have coma along the lines of a parabolic mirror about half the f ratio?

Look, everything is doable.

 

Still, if you ask someone to make it for you, my piece of advice would be to let the guy in charge use the configuration he knows/likes better, being it Fraunhofer or Steinheil, w/o bugging him with a Littrow.

 

IF instead you are going to give it a try as an ATM, you may walk the Littrow path as an experiment.

But do not get too excited at the theoretical ease on paper of R1=R2 and R3=-R2". Not to mention the apparently appealing flat back.

You may find out that such an elegant design -- truly elegant indeed -- is not so obvious to implement under your hands with the due accuracy.

 

Mind you, a 4" f/15 is extremely forgiving; still it has to be done well, otherwise it misses the purpose.

 

 

If you ask me, my own personal preference would be for an uncoated Steinheil doublet with the ED/CaF2 element inside.
This for I *want* to be free to clean the BK7 every single time I wish w/o having to bother with any (more or less) delicate coatings.
In such a simple design the light loss is totally negligible and no spurious reflex arrive at the eyepiece.

 

Anyhow, apart from my personal preference, any well executed design would work.

 

 

Again....thanks for input and interesting conversation...

You are very welcome -- my pleasure: glad to be of help 

[Max Lattanzi]

How about newts with FPL-53 primaries???  

 ...  or better yet, fluorite primaries!   

Nah, nah -- no CaF2: leave FPL53 for primaries.

You should instead use CaF2 for the spider vanes -- imagine: entirely transparent, no scatter (not even with a laser), totally zero diffraction...!

 

AND, by all means do not overlook the Lanthanum glass for the secondary mirror. THAT is a crucial improvement too.

 

That's gonna be a truly dream Newtonian

  

 

 

PS/ If you wish to play tough go curve spider vanes: a good source of the CaF2 would be a couple of 4" FC-100.

Laser cut 2-3mm of the outer part of the lens and those would be perfect.
The rest you can trash -- those are just small apos in the end. 

 

OR, if you wanna play smart, get the outer part of the CaF2 element specifically from two FC-100DL.
Cut also the front element. Re-work the lens cell and put it back on the market as an especially-designed one-of-a-kind (two, actually) FC-95-XDL @ f/9.5 of unprecedented correction.

 

You could even get more money that what you originally paid. And get yourself a bigger dream Newtonian   

[starcanoe]

Thanks again for the input Max.

 

The reason I was interested in the Littrow (or more specifically a design where the two internal radi match) is for the ability to mate them with a thin oil layer. One, you increase transmission (kinda nice) and probably more importantly you reduce secondary reflections creating ghost images. These two features are pretty nice for an ATM made lens where coating the lenses is gonna cost big money...not to mention the fact the coater may break your prized lens. Actually, the flat part of the Littrow bothers me....more possible reflection problems AND I'd much rather make a moderate radius sphere....I know I can do that and get what I need...a flat/near flat....I can see me chasing that thing all over the place.

 

If I ever do an air spaced lens where reflections may be a possible issue...I'd consider just coating the one surface most likely to cause the problem.

 

Again, thanks for the interesting reading.

Edited by starcanoe, 19 March 2018 - 08:13 AM.

[Max Lattanzi]

On a more practical level realizing that the perfect apo remains a dream I decided to stop at 155 F/9 apo and move on to larger long focus Maksutovs of 8” and 10” aperture, these are both F/20’s with 22% central obstruction, cooling is a problem but I now have an effective method to deal with that, and according to Yuri the color correction of these Maks are about an order of magnitude better than the best apo one can find, and, the same mount that can carry a 6” F/9 apo will also carry these larger Maks.

.

Contrast on planets? They are about the same as the apo.

.

Vahe

Vahe,

 

Why a dream? We're talking of a simple 4-inch one and half meter long... I think a dream should be something WAY more inaccessible than that. And still...

 

...imagine how many times that poor fellow named Roland heard something similar when, about 35 years ago, in a market flooded with SCTs, was staying up at night working on what...?! a revival of refractors...?! You're dreaming, man...!! Poor naive fellow...!!! 

Thanks God -- for all of us -- he went on his own road without listening to the crowd.

 

Here we are talking something  way way way way way easier.

 

For instance I can personally touch that "dream" everytime I stop down the TEC200ED at 4". It is exactly that: a 4" f/18 FPL51 flavoured.
Just for fun, of course: I am not going to tell you the TEC200 works better when stopped down at 4".
But certainly the star test is *totally* white with zero aberrations. It looks computer generated. Even better than Alan's Newtonian 

 

Those with a TEC200FL (or similar LZOS, for what is worth) can experience something even slightly better, i.e. a 4" f/16 CaF2 flavoured.

Now that you make me think about it, actually better do it f/16, so that those retrofitting their 4" f/15 vintage refractors would have spare focus to use a binoviewer w/o cutting the tube.

The difference is a mere 10cm in length...

 

 

Further -- curious you mention your Maksutovs (you may wish to know Maks are my secret passion -- I have to check, but probably I own more maks than refractors...would you believe it?

Actually in these weeks I am dealing with the reverse engineering of three of them (7, 10 and 12") to bring their obstruction below 0.20.
It's not just optics, but also A LOT of mechanical tuning to do.

 

Yes, their color correction is better than the apos currently on the market -- not better than the one I've been suggesting though --, but contrast is, as you say, "about the same". About but not at all the same, if you are demanding. And I am not even mentioning sensitivity to seeing (that I am trying to reduce as much as possible by going under 0.20), even when you have reached full thermal equilibrium (which is not always evident) and perfect collimation.

 

All this to try to mimic a refractor over a corrected field of only *a few* millimiters: outside that ***tiny*** spot, as 'large' as the nail of your little finger, you are no longer diffraction limited. Diffraction limited -- I am not talking 0.999 Strehl!
While in your nearby refractor you have a flat corrected field of a few inches instead.

 

So, it does not come as a big surprise that Yuri -- just to name the one you named -- after the early production we all know about, entirely dropped the Maksutov and went the apo way instead. Despite the color correction of the maks being one order of magnitude better, as you rightly recall.

 

Signed: a friend that owns more Maks than refractors 

[Max Lattanzi]

And you can make them unobstructed too, through use of an off axis mask...although for planets I still prefer 20" with ~16% obstruction to 8" with no obstruction. 

But don't you think all of us have been there already...?!

 

Next time you can, try nearby a *quality* refractor equally-sized than your mask -- you will see immediately that it's not at all the same.

Otherwise, why bother? The whole of us would obvioulsy own a large Newton with an off-axis mask.

 

A 20" Newtonian costs nowadays like a set of good eyepieces. Do you think it would pose any financial issue for someone owning, say, a 8" APO (or an achromat FWIW) and wishing to upgrade?
Nonetheless, when a die-hard planetary observer looks to upgrade his 8", that would usually be a 9" or 10" or more of the same flavour. Not a 20" Newton.

 

Why do you think something like this happens? You can speculate for the years to come, but Occam's Razor is there to provide you with the immediate simple answer.

 

 

And, be assured, first time a big mirror will show me what big refractors have shown me, you'll find it fully anchored at the floor of my observatory.

[Max Lattanzi]

Max, I think you're aware that the Lichtenknecker VA Apo triplets were manufactured in F/15: 110, 125, 150, 175, 200, 225 and 250 mm diameter objectives.

 

Does anyone know of an actual 110 mm F/15 Lichtenknecker VA - APO in existence ?

Yes, I am aware of those, but honestly (and sadly) have not found one yet to try.

 

Though, let me draw your attention on the Lichtenknecker table you attached.

 

As you see, the *theoretically calculated* expected RC value for the VA 100/1650 is 0.6, which is exceptional vis-à-vis a regular Achromat, but still nothing more than the *actually measured* RC value of those humble WO 110/7 FPL51-flavoured triplets we were discussing above.

The *very best* apos available today (and yesterday) are between 0.1 and 0.2.

The FPL53/CaF2/OK4 (mutually exclusive, of course) doublet (not triplet) 4" f/16 (OK, yes, let's make it f/16) mentioned above aims at a RC value sensibly below 0.1, possibly flirting with 0, if correctly done.

 

 

You may think of it as an expensive unobstructed newtonian (only as per CA correction), just to please Alan

[Max Lattanzi]

For someone who hates brand touting, you certainly pour it on. I have do doubt about the overall quality of LZOS optics, but I remain deeply suspicious of the kinds of unquantified language, like "take no prisoners." This is no different than what the Takahashi crowd, the Astrophysics crowd, or the entire audiophile community does.

 

Enjoy your scope, whatever it is.

Peter, you can find interferometric reports all over the Net without me sharing with you mine, nor all the observing reports and photographic tests I made of them agains other optics.
That would be perceived as public bashing (and probably rightly so) and start an endless war. So I'd rather chew and swallow all of them.

 

Further please consider that LZOS own internal reports are almost systematically underrating their own optics.
That was immediately obvious when I started using them years ago; checked by chance one day with Markus (and he did confirm).

 

We can speculate on why they do so -- my own personal guess would be that, amateur astronomy market being such an insignificant percentage of their revenues, they are so bugged by the obligation to produce these reports to do it with extreme superficiality -- but it is obviously so. And it is fine with me: since I use lenses and do not take onanistic pleasure in watching a 3D interferometric report framed on the wall while my telescope is closed in its case, I prefer to have an outstanding lens even though the report attached obviously rates it not as high as it should.

 

In the end, happiness is just a few hundred bucks aside: I could send the lens to Wallenform or to Rohr or to many others and have my reassuring accurate report printed in flying colors with my own name on it to be proudly shown to everyone.
But I really do not care.

 

 

This being said, and now getting to the "crowd", I am afraid I was not able to make myself understood so, as a result, you keep missing the point.
Let's see if I can make myself more clear: I am NOT promoting or suggesting you ANY brand.

 

A) I couldn't care less about what you use, given it makes you happy;
B) I receive no money from any firm;
C) I have zero -- ZERO -- ownership pride;
D) The sole thing I am interested in is KNOWLEDGE.

 

This is what I have been trying to do with you: knowledge sharing. This is indeed the ONLY possession I care about.

 

 

You see, you cannot find a *single* person telling you that I showed up at a star party bringing ANY instrument (if not specifically requested so). Never and ever.
Every time I go is to see other people instruments. I am there to learn and to help in fixing or improving, not to show how hunky I am for I own this or that.

 

Not only I use telescopes to observe, but I also like to STUDY them, do reverse engineering, and improve them as much as possible.
And I have no personal attachment to any of them because, due to this fact, in any of them I eventually get to capture defaults. So, if you wish, once this happens the 'magic' is gone.

 

Once I've studied them, ALL my LZOS went to someone else. This was before I was on financial need for Refractorland.
Today, I only keep one single LSOZ with me (and I am not telling you which one, as you see).

 

Of the TEC and the WO you already know.

 

After I sold all my APs, I have kept for me and old Christen triplet (still not telling you which one).

 

Three Takahashi are with me. You do not know which one.
Or, rather, if you look around you may discover that one is a humble Sky-90II.
Why? Exactly because, as it is the case with the WO 110/7 discussed above, it is a constantly bashed and underrated instrument.
And I wanted to make it as perfect as possible -- what I did, improving it till it was not testing even (CA apart) vis-à-vis a Stowaway (which is, within its limitations, an *outstanding* piece of optics).

 

Yes, Stowaway is also gone -- three of them, actually.

 

More? Yes, I think I have four Zeiss left. For various reasons, from sentimental, to historical, to scientific.
Also a bunch of no-brand exotic stuff which belongs to my experiments.

 

And you know what? As you might have read before, I have more Maksutov than all of the refractors above.
And I think have more Celestron SCTs than all of the above together.

 

Yes, a bunch of SCTs.
I like to open them up, measure, study, modify, put them back together to do things beyond what they were ever able to do.
Or, rather, things that were in the mind of the designer (and sometimes even beyond that) but never materialized for various construction constrains.

 

I could indeed write a rather thick book on how to improve Maks and SCT more than on refractors (where room for improvement is, in the end, rather limited due to their inherent simplicity).

 

So...?!
Who am I? A LSOZ aficionado? An AP fan? A TEC enthusiast? A Takahashi fellow? A Mak person? A Celestron man...?!?!

 

Did you ever hear from me once the suggestion to buy any of the above because I own them...?!
Or that they are superior to others for I decided to buy them and I have to self-justify my purchase ...?!
Did you ever hear me being defensive for you have dared to touch anyone of my own precious...?!
Can you find a single line of me in any of the forums, laughing at the issues of a fellow astronomer and, instead of being of help on the specific subject, suggesting him to trash, say, his lessen SCT and buy an expensive apo refractor instead...?! (*)

 

In the end, where do you like to frame me...?! Which crowd do I belong to...?!?!

 

It's all about knowledge, Peter. Just knowledge. And sharing thereof.

 

Take care  
-- Max

 

 

(*) Incidentally, and laughs apart (which are always very welcome), it would be nice if, *for once*, a technical exchange on the use of some glasses in the design of refractors, would not end up by rolling the dice with the usual bunch of off-topic suggestions, made on the basis of personal decisions to have eventually chosen a different kind of telescope, being it Newtonian, Cassegrain, Makustov, Schmidt, Ritchey–Chrétien, TriSchiefspiegler or whatever else. All legitimate personal choices, of course. But entirely off topic with the title of the discussion (not to mention the main heading of the forum).

 

In any motorbike forum, when dealing with, say, the stability of a certain bike model on a circuit, would you find it useful if someone would chime in and, as a constructive contribution, would suggest to trash the two wheels and get a car instead...?!
Would that make any sense...?! I really do not think so.

[Max Lattanzi]

Patek tried for decades to produce a high beat movement, and failed. ETA succeeded, even Seiko succeeded. Even the Chinese succeed. Bad example. Bottom line, there is no reason to buy a telescope with a very long f-ratio, when a shorter f-ratio scope will do the job, and require a smaller mount for a larger aperture. Yes, call it "an exercise in style." It's certainly not practical.

Peter, watchmaking is not a race towards the fastest beat movement but about final precision in the mechanism. Leaving apart complications.

 

If I'd report your sentence to the Master Watchmaker mentioned above, *for sure* he would look at me with a smile saying: "you know, having *every single specimen* we produced being thoroughly measured and then certified as "Chronometer", WHILE using a highly reliable (Patek's standard of high reliability) low-beat movement, plus additional complications, THAT is the achievement that tells you something about the quality level and precision of our work here"...

 

Very simple.

 

As a result, I do not recall ETA or Seiko or any Chinese watch being exposed in Museums or being auctioned for millions.

 

So, as fa as I am concerned, the example remains a good one.

[Max Lattanzi]

It is surprising that those remaining samples haven't been snapped up by purchasers eager for near perfection in an apochromatic triplet of manageable size.  Such old stock of a superb apochromat languishing un-bought on the shelves of APM would seem to support your basic arguments about actual current market interest in high-quality long-focus refractors.

Well, you know, as mentioned above, you should consider the lack of sexyness of the 'dull' LZOS.

 

If those 130 f/9.2 were labelled, say, Astro-Physics or Takahashi (or Zeiss), you can bet your yearly salary they would all sell within a couple of hours with several threads full of wow, yeah, great, etc. etc. appearing all over CN.

Same would happen for the CFF 4" f/10 (and any similar other), of course.

 

It has nothing to do with optics and Astronomy. It's mere pride of ownership at work.
We all know that. 

[Max Lattanzi]

In any case, I have found your contributions to this thread to have a straightforward clarity and to be interesting, informative, and entertaining, while also provoking comment from others.  I thank you for them.

You are very welcome.

And I am the one thanking you for the time devoted and the documentary research you made.

 

I am pleased if I was able to help you out in finding something new. 

[Max Lattanzi]

That’s what I did, buying a 5" f6.5 AR127 ;-). Still, the stars are bloated compared to the view through an apo. It does the job and it’s nice for the price paid but you get what you pay for.

Smart move

 

Yes, obviously you always get -- at best -- what you pay for: no manufacturer is Mother Theresa or a missionary.
If they were so, they would swiftly close business.

 

But, I mean, what kind of power are you using to see bloated stars? You mentioned low-power...

 

In any event, I personally consider Akira Fujii bloated Pleiades one of the most beautiful things one can watch in the night sky.
If your views are similar that, you're a happy man

 

This being said, if you want to really improve your views, after a 6" f/6 and a 8" f/6, try to walk the path of a good large binoscope.
That is another world all together.

 

For deep-sky low-power views I went the same direction and am almost finished with a custom 6" binoscope, using 3" and 2" prisms for a 100% illuminated field on 2" eyepieces (35PO, 20NT2, etc.).

A lot of work but, I am telling you, a different world.

[Max Lattanzi]

A six inch F18 with a 50mm plossl would have nearly a one degree wide real FOV...plenty of deep sky objects where that is more than enough.

 

You can do even better: get yourself a 3" or 4" focuser and start using 3" eyepieces.
I personally got a 3" 50mm 70° which, on that scope would give almost 100 arcminutes of true field entirely flat, fully illuminated and corrected up to the edge.
Slip inside a 0.75x 3" reducer and you are at almost 2 full degrees (1.8, actually).

 

There are a few nice eyepieces around like that. Not very many, though.

 

It's an extreme use, of course, which shows the inherent beauty and flexibility of the refractor design. For instance, you cannot do that with a planetary Maksutov that, despite any large thread you can put on its back, remains an instrument conceived to be "refractor-like" on the field of 0.965" eyepieces (you can use larger, of course, but the song remains the same).

 

Anyhow, there is no perfect telescope for everything in the end.

No matter how much you work on the 6" f/18 -- you can also use custom-made 4" eyepieces, for instance -- a good short-focus refractor would always be ahead in approaching 7mm p.u and a wide field you will never get.

 

No need to feel desperate for that -- the good news is that no medical doctor have ever forbidden to get more than one scope

 

Cheers,
-- Max

[Max Lattanzi]

I rarely ever think about the need for a wider fov visually using my 8" f15.5 and 31mm Nagler. And if I do I look through my 6" f12. Wide field imaging is another matter, but at the same time many fast scopes dont have enough image scale to frame most medium and small objects nicely or bring out detail unless they have a lot of aperture using todays large format cameras. I get that some like to scan at low powers and wide fields. But I like to scan at higher powers and smaller fov as you get increased contrast and can actually see things like small planetaries, small faint globulars, close doubles.

Richard, if I may, same piece of advice.

 

With your 6" f/12 and the N31 you get 1.3° true FOV on 2".

With your very same FL, the 8" f/9 I have here, thanks to the larger focuser and the 3" 50mm eyepiece mentioned above, gets 2 full degs, almost twice and half the area.

Slip inside the 0.75 reducer and you get up to 2.75 full degrees, which is 450% lager true field of view than your starting point. With your very same telescope.

 

Worth it.

 

Gotta go now.
Ciao!

[starcanoe]

Yes on the 3 or 4 inch eyepieces for wide field of view with long refractors.

 

I lucked upon some surplus optics...I'm pretty sure its a 3 inch orthoscopic set! Probably works darn well at high F ratios'.

 

I've also been playing over the past few years with surplus lenses and stuff salvaged from large camera lenses/telephoto lenses/teleconverters/etc.....I think I can rig up some nice large format low power eyepieces now.

 

And for that matter...if you have a 6 inch f15 say....if you can't get the really low power....just get a darn 6 inch f5 to compliment it and only use that at its lowest power.

 

One of my favorite taped together ATM projects was a 60mm fl 700mm with a surplus 50mm plossl. Cheap, easy and darn high performance low power viewing.

[Jeff B]

"So, it does not come as a big surprise that Yuri -- just to name the one you named -- after the early production we all know about, entirely dropped the Maksutov and went the apo way instead."

 

Well, not quite correct as Yuri has released limited subsequent runs of the 6 & 7 inch versions of which I have a 7".  And I have to tell you that my 7" does indeed have exceptional optics and I was quite surprised as to how well it compared to the 200ED one night on the moon and Jupiter.  I can honest say the bulk of the differences were mostly due to aperture differences (though the 200ED was slightly "warmer" in color tint).  I recently wrapped the 7 with a couple layers of Refelectix insulation per the subject of another thread here and it's now an all season scope where as before it was a fair weather friend only.

 

Jeff

[vahe]

 

Further -- curious you mention your Maksutovs (you may wish to know Maks are my secret passion -- I have to check, but probably I own more maks than refractors...would you believe it?

Actually in these weeks I am dealing with the reverse engineering of three of them (7, 10 and 12") to bring their obstruction below 0.20.
It's not just optics, but also A LOT of mechanical tuning to do.

 

Yes, their color correction is better than the apos currently on the market -- not better than the one I've been suggesting though --, but contrast is, as you say, "about the same". About but not at all the same, if you are demanding. And I am not even mentioning sensitivity to seeing (that I am trying to reduce as much as possible by going under 0.20), even when you have reached full thermal equilibrium (which is not always evident) and perfect collimation.

 

All this to try to mimic a refractor over a corrected field of only *a few* millimiters: outside that ***tiny*** spot, as 'large' as the nail of your little finger, you are no longer diffraction limited. Diffraction limited -- I am not talking 0.999 Strehl!
While in your nearby refractor you have a flat corrected field of a few inches instead.

 

So, it does not come as a big surprise that Yuri -- just to name the one you named -- after the early production we all know about, entirely dropped the Maksutov and went the apo way instead. Despite the color correction of the maks being one order of magnitude better, as you rightly recall.

 

Signed: a friend that owns more Maks than refractors 

 

Maksutovs are also my passion, in the early sixties I made one as my last ATM project, it was based on John Gregory’s 6” f/15 design that appeared in sky and Telescope magazine, this particular model had a spot secondary and required an aspheric primary, I learned the hard way that aspherizing a primary was way over my talents and the results turned out to be a disappointment.

.
To me Maks are the most ideal compromise when it comes to their potential as high power planetary telescopes, I just do not care much for Newtonians, its just a personal preference.

.
As for field of view, my two F/20’s have a fully illuminated field of about 1mm in diameter, tiny as you say, but the light fall off is not very noticeable when viewed in an orthoscopic eyepiece of relatively narrow field. The 1mm illuminated field is roughly the size of Jupiter in the 10” Mak.

.
And yes, Yuri abandoned 8” and larger Maksutovs a while back, in an early post he blamed glass quality as one prime reason but I personally believe that refractors are more profitable for maintaining a healthy business compared to Maks which have a much limited market appeal and are harder to produce, also Yuri never seriously addressed the cooling issues of his Masksutovs and for all practical purposes TEC Maks rely on passive cooling to stabilize which makes his larger Maks hopelessly problematic.

.

Vahe

[Peter Besenbruch]

Peter, you can find interferometric reports all over the Net without me sharing with you mine, nor all the observing reports and photographic tests I made of them agains other optics.
That would be perceived as public bashing (and probably rightly so) and start an endless war. So I'd rather chew and swallow all of them.

No-one is arguing that LZOS makes poor optics. I have been arguing two points which you consistently do not address:

 

1) A medium focal length, ED refractor has considerable advantages over a long focal length one. It is possible to either use a lighter mount, or a larger size on a given mount. The larger size will show more. At the same size, a well executed medium focal ratio refractor will in practice show the same detail.

 

2) There is no practical difference between a well executed FPL53/Fluorite/OK4 lens. No, I don't buy the secret formula makes LZOS better argument. Neither do I accept that there are magic beans.

[Peter Besenbruch]

Peter, watchmaking is not a race towards the fastest beat movement but about final precision in the mechanism. Leaving apart complications.

 

If I'd report your sentence to the Master Watchmaker mentioned above, *for sure* he would look at me with a smile saying: "you know, having *every single specimen* we produced being thoroughly measured and then certified as "Chronometer", WHILE using a highly reliable (Patek's standard of high reliability) low-beat movement, plus additional complications, THAT is the achievement that tells you something about the quality level and precision of our work here"...

 

Very simple.

 

As a result, I do not recall ETA or Seiko or any Chinese watch being exposed in Museums or being auctioned for millions.

 

So, as fa as I am concerned, the example remains a good one.

High beat watches are a sign of a level of engineering that Patek isn't capable of. Patek is all about external finish. They are second to none in external finish. I thought your Patek example strange, because you were using Patek to defend LZOS. Patek is the anti-LZOS.