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Roland's 10" Mak versus a 10" f/5 reflector

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#1 azure1961p

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Posted 26 April 2013 - 08:25 AM

The scopes:

10" f/14.6 Mak 23% co
10" f/5 newt 26% co

Ok, no doubt Roland's Mak is corrected to a higher degree than any 10" f/5, too a paracor would eat up the throughput advantage of the newt s simple design but that still makes it seem like the reflector has a fighting chance to match this $10,000 OTA Mak.

So what's going on here? Is Roland really getting 10" f/5 planetary performance? Or is the ability to perfect a maks optics so much better than a similar parabola that no reflector in that size can realistically hope to compete?

Pete

#2 dbledsoe

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Posted 26 April 2013 - 09:00 AM

Do you own either of those scopes? Not sure what the point of this thread is... No offense intended, just curious.

#3 Darren Drake

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Posted 26 April 2013 - 09:16 AM

If you're talking about on axis performance any well made 10 inch f/5 or so newt can absolutely compete with the high end mak as long as the secondary obstruction percentages are similar. Off axis performance would goto the mak but a paracorr would offset that advantage. The light loss from the paracorr is a complete non-factor.

#4 Asbytec

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Posted 26 April 2013 - 09:31 AM

So what's going on here? Is Roland really getting 10" f/5 planetary performance? Or is the ability to perfect a maks optics so much better than a similar parabola that no reflector in that size can realistically hope to compete?

Pete


Pete, I love MCTs and whenever the topic of those nice 10" MCTs pops up, I get excited.

Its really interesting how spherical optics make horrible telescopes, but they can do so much with the caustic focus they can be quite good. Smooth and corrected using additional spherical lens while tossing in that troublesome higher order SA. Still, one this size needs some aspheric term to work as advertised and can be corrected quite well.

Still, a Newt uses a parabolic curve which is ideal for forming a spherical wavefront to some level of precision and cost. It'll deal with less surfaces and employ no lens to absorb light.

Which would work best on planets? I love my MCT on planets so I'd tend to want to vote for the 10" MCT...as dream, refractor-like scope when cooled and collimated. But a good 10" Newt is no slouch.

Does the 10" MCT really have better reflected light and contrast control? At least both should be affected by seeing about the same way.

I dunno, Pete, for one of those comparison threads, you picked a doozie. I'd take the 10" MCT though, if the opportunity arose, primarily because I love the design. They are "pleasing" designs.

#5 bierbelly

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Posted 26 April 2013 - 09:49 AM

IIRC, there's a picture of something through the AP 10" MCT in the current issue of S&T.

#6 azure1961p

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Posted 26 April 2013 - 09:58 AM

Do you own either of those scopes? Not sure what the point of this thread is... No offense intended, just curious.


I'm not understanding the point of your post to be quite honest. Ownership is not a prerequisite for query. As it is I'm the former owner of a fine 10" f/5 that simply was an unimpressive planetary scope. After several months and not a single wow moment I sold it and was never happier. That said it'd be odd for that beast to be seen as a challenger to a $10000 Mak OTA.

Pete

#7 Jon Isaacs

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Posted 26 April 2013 - 09:58 AM

From memory:

It's probably worth noting that Roland's 10 inch MAK is hand figured by Roland and I believe it is somewhat aspheric. The optics were designed by Valery Deryuzhin of Aries Optical. It also has mirrors made from zero expansion materials and it has cooling ports. I also believe it has a removable baffle for Planetary work that allows for a 22% Central Obstruction.

The thing about the A-P Mak is that it was designed as a system, not just high end, near perfect optics but matched optics in structure optimized... I believe they were $10,000 new, the last one I found that sold was $30,0000 in 2009.

I have to believe that the 10 inch A-P mak is about as close to perfection as any 10 inch scope can be. I think the question would be whether Roland could build an 10 inch F/5 Newtonian that equaled it's performance. He would probably build a Mak-Newt...

One other note: Pete mentions a 10 inch F/5 with a 26% CO. A 10 inch F/5 Planetary Newtonian would have a much smaller CO, a standard configuration with a low profile focuser allows for a 19% CO with a fully illuminated field of view of 19%.

Jon

#8 Eddgie

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Posted 26 April 2013 - 10:51 AM

Yes, I agree that if the CO is kept about the same and the quality (Zambuto, Royce, etc) is about the same, the scopes should perform to about the same level on axis.

The MCT may have better off axis performance, but then again, it is limited to a much narrower true field. If the 10" f/5 scope were limited to the same size true field the coma would not be all that serious an issue.

The AP could give a pinpoint field with a 41mm Panoptic, but the power would be .72 degrees.

If I used a 27mm Panoptic in the 10" reflector, I would limit the field size to .76 degrees (slightly larger than the AP, but because I am not looking as far off of center as I could get with something like a 35mm Pan, the coma would be far less of a factor.

And I could use a Paracorr is I wanted to, and still have a scope that is only 1500mm in focal length vs 3000 for the 10" AP.

There was a thread a while back that pitted a 250 Mewlon against the 10" AP and I picked the 10" AP on that one.

For that one, the Mewlon had a meaningfully bigger CO, but more importantly, the bench tests I have seen on Mewlons have led me to believe that they are not made to the same high level of perfection that you would get from either the AP or a custom mirror Dob.

And as to the relevance of the OPS post... Just about anyone that can afford moderately high end 4" APO (Televue or Stellarvue for example) can afford to buy a 10" Go-To Newtonion ($1300) and have the mirror custom refinished (maybe $800 for re-finishing and re-coating)!

For someone wanting a telescope that would go head to head with the AP 10" for less than the price of a little expensive toy telescope, they could have a fantastic planetary scope.

And that includes the tracking mount!!!!!

Yes, I am mocking the refractor community by calling their telescopes little expensive toys.

Don't hate me because physics is beautiful.

Oh, and I think that the reason the AP has aspherized optics is that it is difficult to make a 10" MCT faster than about f/22 that doesn't suffer from some higher order spherical aberration.

The way to manage that is to aspherize one element, most likely the curve of the meniscus on one side. OMG, that has to be hard.

And Mr. Christen even said so as I recall. It seems to me that many years ago he commented that the hand figuring was far more difficult than he would have thought, and did not know if he would ever build another one...

#9 Paul G

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Posted 26 April 2013 - 12:18 PM

From memory:

It's probably worth noting that Roland's 10 inch MAK is hand figured by Roland and I believe it is somewhat aspheric. The optics were designed by Valery Deryuzhin of Aries Optical. It also has mirrors made from zero expansion materials and it has cooling ports. I also believe it has a removable baffle for Planetary work that allows for a 22% Central Obstruction.

The thing about the A-P Mak is that it was designed as a system, not just high end, near perfect optics but matched optics in structure optimized... I believe they were $10,000 new, the last one I found that sold was $30,0000 in 2009.

I have to believe that the 10 inch A-P mak is about as close to perfection as any 10 inch scope can be. I think the question would be whether Roland could build an 10 inch F/5 Newtonian that equaled it's performance. He would probably build a Mak-Newt...

One other note: Pete mentions a 10 inch F/5 with a 26% CO. A 10 inch F/5 Planetary Newtonian would have a much smaller CO, a standard configuration with a low profile focuser allows for a 19% CO with a fully illuminated field of view of 19%.

Jon


The AP Mak has a heavily aspherized primary, very smooth, with at minimum 1/10 wave optics (system), zero coma, and is permanently collimated. A long focal length 10" Newt with excellent optics could come close on axis, except for the effects of the spider vanes and any dust on the mirror in the open system on contrast. Excelsior optics used to make a 10" f8 newt for planetary imaging, it produced some superb images. Roland was asked to compare his 10" Mak with Excelsior's 10" f8 newt and he said:

Link

#10 Paul G

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Posted 26 April 2013 - 12:36 PM

Oh, and I think that the reason the AP has aspherized optics is that it is difficult to make a 10" MCT faster than about f/22 that doesn't suffer from some higher order spherical aberration.

The way to manage that is to aspherize one element, most likely the curve of the meniscus on one side. OMG, that has to be hard.

And Mr. Christen even said so as I recall. It seems to me that many years ago he commented that the hand figuring was far more difficult than he would have thought, and did not know if he would ever build another one...


It took Roland nearly one year to complete the optics on about two dozen 10" Maks. He said it was a real "hair puller" and that Valery's design was "very elegant but a b***h to make." He has posted that any Maks he makes now will be all spherical and that he will never make such a complex design again.

Initially he was hoping he could import the optics, manufacture the ota, assemble them and have a large aperture lunar/planetary scope that would be easy to make and would satisfy those on his large refractor list. However, once he started it became an exercise in making the most perfect optimized lunar/planetary scope possible, and he did. The coatings alone cost AP nearly $2000 per scope. He even did extra aspherizing of the already heavily aspherized primary to give the scope identical inside and outside star test patterns. Sweet, but the net result was that it was not practical to manufacture long term.

The AP 10" Mak with a MkV binoviewer and ZAO's absolutely screams on the planets. When experienced observers look through it for the first time their unsolicited initial comment is almost always about its superb contrast.

#11 saemark30

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Posted 26 April 2013 - 02:37 PM

Looking through a couple of custom 10" F/6 Newtonians with low expansion material, Antares or Prototype secondaries and fans I have seen more detail on Jupiter, Saturn and Mars through that than any MCT or 6" refractor. That is, if the conditions are right.
I have never looked through the AP MCT, but a custom 10" Newtonian only fault is a slight vane effect, otherwise it can be refractor-like in the good sense.

#12 DJCalma

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Posted 26 April 2013 - 02:45 PM

A 2.6" secondary has no business being in a 10" F/5 system. Even if it could be replaced by a 1.83" with full illumination, I'd take the Mak on all days that end in Y.

#13 azure1961p

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Posted 26 April 2013 - 03:10 PM

Lol, Ed you never disappoint. The physics/beautiful line ought to be your signature.

Pete

#14 azure1961p

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Posted 26 April 2013 - 03:29 PM

From memory:

It's probably worth noting that Roland's 10 inch MAK is hand figured by Roland and I believe it is somewhat aspheric. The optics were designed by Valery Deryuzhin of Aries Optical. It also has mirrors made from zero expansion materials and it has cooling ports. I also believe it has a removable baffle for Planetary work that allows for a 22% Central Obstruction.

The thing about the A-P Mak is that it was designed as a system, not just high end, near perfect optics but matched optics in structure optimized... I believe they were $10,000 new, the last one I found that sold was $30,0000 in 2009.

I have to believe that the 10 inch A-P mak is about as close to perfection as any 10 inch scope can be. I think the question would be whether Roland could build an 10 inch F/5 Newtonian that equaled it's performance. He would probably build a Mak-Newt...

One other note: Pete mentions a 10 inch F/5 with a 26% CO. A 10 inch F/5 Planetary Newtonian would have a much smaller CO, a standard configuration with a low profile focuser allows for a 19% CO with a fully illuminated field of view of 19%.

Jon


The 2.6" secondary is a Parks spec and Im almost positive the same size I had with my Parks 10" F/5 . There's no way in heaven at least my secondary was anything close to 1.8" in that f/5. It was this FAT thing and if it wasn't 3" it was certainly 2.6". I believe the 2.6" besides the 10" f/5 Parks is also the same size for the Orion XT10. Moreover GSO also goes with a similar sized secondary for its 10" f/5 optical set. We can all shave our secondaries down Jon but the fact is three things begin to rear their head:

1. Collimation becomes more critical in centering the primaries reflection
2. Some oculars may show vignetting
3. The edges of flats are often prone to error if there are errors to be had.

I could arguably make my 8" reflectors secondary the size of my thumbnail but to no gainful benefit.

DJ: its actually good business if you look at the reflectors sold over the last couple decades anyway.
Pete

I can fish out links if its required.

#15 DJCalma

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Posted 26 April 2013 - 04:10 PM

My 10" F/4.5" has a 2.14" secondary and so do several other 10 inchers in my club. One member's scope is a 10" F/7 and has a 1.83".
The only 2.6 incher I've seen is the stock secondary in my lowly Coulter. A newt these days with a 26% obstruction is absurd unless it comes in around F/2.8 or so.

#16 gnowellsct

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Posted 26 April 2013 - 04:11 PM

I think the ten inch Mak went for $10 or $12 k, and on the used market will be bid up to $35 or $40 k. Mainly a prestige item. The question then is what could you do for that kind of money that would out perform it. And there the answer is a 14 or 16 or 18 inch just-about-anything. As with all AP products the ten inch Mak is an ultra precision optical work of art where all elements of design have been thought through. Greg N

#17 amicus sidera

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Posted 26 April 2013 - 05:17 PM

Just about anyone that can afford moderately high end 4" APO (Televue or Stellarvue for example) can afford to buy a 10" Go-To Newtonion ($1300) and have the mirror custom refinished (maybe $800 for re-finishing and re-coating)!
For someone wanting a telescope that would go head to head with the AP 10" for less than the price of a little expensive toy telescope, they could have a fantastic planetary scope.

And that includes the tracking mount!!!!!

Yes, I am mocking the refractor community by calling their telescopes little expensive toys.

Don't hate me because physics is beautiful.


:bow: :applause:

#18 Jon Isaacs

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Posted 26 April 2013 - 06:34 PM

The 2.6" secondary is a Parks spec and Im almost positive the same size I had with my Parks 10" F/5 . There's no way in heaven at least my secondary was anything close to 1.8" in that f/5. It was this FAT thing and if it wasn't 3" it was certainly 2.6". I believe the 2.6" besides the 10" f/5 Parks is also the same size for the Orion XT10. Moreover GSO also goes with a similar sized secondary for its 10" f/5 optical set. We can all shave our secondaries down Jon but the fact is three things begin to rear their head:

1. Collimation becomes more critical in centering the primaries reflection
2. Some oculars may show vignetting
3. The edges of flats are often prone to error if there are errors to be had.

I could arguably make my 8" reflectors secondary the size of my thumbnail but to no gainful benefit.

DJ: its actually good business if you look at the reflectors sold over the last couple decades anyway.
Pete

I can fish out links if its required.



Pete:

I am not sure what your goal is. If you are trying to compare a Parks 10 inch F/5 Newtonian to Roland Christen's legendary 10 inch Mak, I think everyone agrees that the Parks scope would not be up to the task. It's not an optimized design and many aspects of it are crude, Parks scopes haven't changed much in the past 35 years or so.

This is the question you ask:

"Or is the ability to perfect a maks optics so much better than a similar parabola that no reflector in that size can realistically hope to compete?"

The Parks is not relevant to this question. People do build 10 inch reflectors with small central obstructions by using low profile focusers. They do use mirrors that are tested and figured using interferometers, just as Roland does, they use zero expansion substrates just as Roland does... Consider that Roland removes the baffle to reduce the central obstruction because the light leak is not relevant when viewing the planets...

Jon

#19 *skyguy*

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Posted 27 April 2013 - 07:24 AM

A 10" ... is a 10" ... and always will be a 10". The ultimate end performance is all about design, execution and attention to detail ... and money spent!

#20 amicus sidera

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Posted 27 April 2013 - 08:12 AM

A 10" ... is a 10" ... and always will be a 10". The ultimate end performance is all about design, execution and attention to detail ... and money spent!


Precisely.

My question is: which 10" f/5 reflector, made with what level of optical quality, versus this vaunted 10" Mak?


Fred (who, after almost fifty years at this, remains unimpressed by "legendary telescopes", having actually had the opportunity to observe through many so designated)

#21 azure1961p

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Posted 27 April 2013 - 09:02 AM

The PARKS is relative to the example as a model or example of a typical classic 10" f/5 . True, they haven't advanced in 35 years and much to the detriment of their business. At anyrate being that they are so prevalent (reflectors in this size and speed) and that it shared some specs with the Roland -Vallery Mak the comparison seemed worthwhile and revealing of both pluses and minuses in both systems.

You could make the argument that an optimized 10" newt bridges the gap better but that wouldn't be representative of the common reflector in this size most people seem to own.

Pete

#22 Eddgie

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Posted 27 April 2013 - 09:29 AM

10" f/5 that simply was an unimpressive planetary scope.



You are comparing a telescope that was crafted over a years time by one of the leading optical fabricators on the planet to a telescope that was most likley not.

The CO you site also understates the real obstruction which is more like 28%. This is because the secondary size alone does not constitute the entire obstruction. A very thin vane spider will ad 2" to the obstruction, and this assumes a very thin. Many time, the spiders are made a bit thicker than the minimum so it is possible that 3% is more realitic, which brings the obstruction to something like 29%.

But it gets worse. Often, the focuser tube will extend very slighty into the light path of a Newtonian when using eyepecies with a field stop located far up in the barrle.

We don't know if this was the case for your particular scope, but I have seen it enough to know that it is not at all uncommon. This may add another couple of percent of obstruction.

But the biggest difference here is optical quality.

The AP is without doubt most liklely to be pushing a strehl of .98%.

I have a serious doubt that the Parks is in this stratified quality level.

And finally this. Planetary Observing rarely presents a "Wow" because seing for most of us is simply not that good.

I spend an hour or two glued to my binovierers to get glimpses of detail on planets. I don't just sit down and see it all. It comes and goes.

Were you patient? Or did you just sit down and expect to see pictures like we seen in the solar system imageing forum?

On my best nights, I don't see Jupiter as well as even so-so images taken with cheap planeatry cameras. One has to remember though that the planeatry camera does what I do, but it does it in five minutes. It watches and takes thousands of images, and the software selects the best images and combines them together.

And that is what I do. I sit and I watch, and I wait. And after several dozen moments of steadiness in the images over an hour or two, I do the same thing. I "Stack" these images in my brain, and I wind up with a mental image that shows much of the detail that the CCD camera captured.

But not all. The eye simply is not a sensitive and lacks the resoltuion of a modern CCD camera.

Summary: Your telescope is more obstructed than you think, and there is a huge probability that the quality is not on par with what we can reliably expect to be one of the finest set of optics ever made.

And my hunch is that you did not exercise the patience necessary to do planetary observing to the level your instrument was capable.

#23 Eddgie

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Posted 27 April 2013 - 09:48 AM

I have plotted the two scopes.

The AP was plotted as being perfect optically an that is because we can assume that it is.

The Parks was plotted with a 29% obstruction (to reflect the added diffraction of the spider which I doubt was an optimized thin vane type).

I also plotted the Parks with a single optical defect, which was 1/8th wave of spherical abberation.

Now this represents a mirror of far better than average quality. Most mirrors produced today are not nearly this perfect just on spherical abberation.

Most will have other very small errors like some amount of surface roughness, and usually a very small amount of astigmatism or other on-axis errors.

Usually the only time you get a mirror as good as the one I plotted here is if you pay for a custom mirror.

Anyway, the plot on the right represents the quality of a Newtonian that many of us would be thrilled to have, and my guess is that it represents a level of quality that is above the level that your instrument had.

Notice that at every point on the MTF plot, the AP maintains more of the initial contrast than the Newt.

The CO is the major contributor, but again, I was very kind to the Parks and gave it only a single, minor optical error. The vast marjority of mirrors made today are not this good.

A 10" f/5 reflector could be made to do as well as the AP, but the one you owned could not be expected to come close.

Attached Files



#24 Eddgie

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Posted 27 April 2013 - 09:58 AM

If you are not famaliar with MTF, the solid red line represents the contrast loss of a perfect, unobstructed aperture 10" in size.

The dotted lines represent the additional amount of contrast lost due to optical quality issues or obstruction.

If you worked down from the top of the chart at .4 on the X axis, you would see that even a perfect 10" unobstructed instrument would loose mybe 47% of the contrast at .4 of its maximum linear resolution.

THe AP would loose an additional 7% or so, for a combined contrast loss of about 56%.

The 10" 29% obstructed with 1/8th wave would loose about 62%. This way you can find out how the scopes would transfer contrast on varius sized details, The left side represents large details, and as you work to the right, smaller sized details.

The .4 line represents detials that would be maybe 3 or 4 Airy Disk diametars of the instrument. In a 10" scope this might be detail taht was 2 or 3 arc seconds in size.

Now if you are looking at Jupiter, and it is 35 arc seconds across, this should give you the idea. We would be looking at medium sized pale ovals as an example. These are difficult contrast targets for a smaller apeture, and at 8" or 9" of good apeture, under good seeing, and with patience, will start to show more reqularly.

#25 azure1961p

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Posted 27 April 2013 - 04:31 PM

Edd,

I'm at work - I just read through your posts. Can't reply now but I believe the MTF does a fine job of fog lifting here and I appreciate your working through the details in presenting the comparison.

Pete






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