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Maksutov versus Schmidt

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#26 Jeff B

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Posted 01 November 2015 - 09:16 PM

The first photo is unprocessed but shows the seeing that night. The second is the same photo  processed with RigiStax 6 . I used a Quantum 6 Mak 33% CO, that I have had since 1978 and an old Orion StarShoot imager III camera.   I would rather observe than image but on a poor night I can get pretty good results imaging because I can stack fleeting moments.   My Mak has never taken a back seat to any SCT in over 35yrs until I got a mint 30yr old Super C8 Plus last summer.  I used to laugh years ago when I read Celestron had 1/10 wave optics. I'm not laughing anymore.  Since this SCT can run with my Mak,(big CO and all) the advantage is 8" vs 6" and it is much lighter than the 6" Mak.  They say Celestron SCTs are lighter than the same size Meade.   I will leave the reflector, both dob and eq mounted to others, although I have a C5 with very good optics that I would take over the wonderful RV-6 that I had years ago because the C5 is sooooo easy to move around.   I don't have any experience with large refractors but I am enjoying a 60mm mounted on my new to me C8 for its low power wide field views. 

Cool.  Could you give some specifics as to the number of frames, percent used, wavelet settings and stuff like that?

 

IME, the Super C8 introduction marked a turning point toward quality for Celestron.  Nice scope.  I've a friend who has a Nexstar version C8 and it's optically excellent too.  They are noticeably lighter than the Meades and thermally "quicker".

 

There are practical advantages of a Mak relative to a SCT: The slower thermal mass of the thick meniscus takes longer to dew up, plus, as it has no optical power, heating and cooling of the meniscus does not contribute much degradation during the instrument's heating & cooling.

 

Jeff


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#27 maadscientist

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Posted 01 November 2015 - 09:19 PM

So what makes a Maksutov so much sharper than a Schmidt?

 

In a shootout, my 7" Mak easily beat out my 8" SCT. I still like the lighter weight SCT but at these sizes, I can carry either one easily. I had aperture fever and can say that at larger sizes, I don't like to carry any telescope, (but still do).

 

To answer two earlier questions, I am strictly visual. I also spend lots of time collimating. On my 16" Dob, I use a TuBlug and collimate on every object. I use an artificial star for my  Cassegrains.

 

So what is it about the Mak that makes it so good? And in a similar tone, what is it about Dall Kirkhams or iDK's that make them so sensitive to temperature, (or is it that their owners are just that much more sensitive)?

 

Clear skies,

Peter

Collimating on an artificial star is probably an issue. Position of the primary is way off vs live focused images for one thing.....

 

I would collimate on a star, and make sure it is on the side of the meridian where you want to do your observing on....



#28 Ptkacik

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Posted 01 November 2015 - 09:31 PM

Collimating a Cassegrain on a real star? Ok, makes sense. Now I just need to get a clear sky. It seems like it has been raining for a month.

 

But does that explain the Mak/SCT difference? They were both collimated with the artificial star before my shootout that the Mak won so easily.

 

Clear skies, 

Peter



#29 maadscientist

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Posted 01 November 2015 - 09:54 PM

I assume you have a Rumak if you can collimate the MCT....

 

Can't really answer that until we can confirm that a side by side test was done collimating on a live star under good seeing... then you can look at the star test as well for further info...



#30 vahe

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Posted 01 November 2015 - 09:59 PM

 

But does that explain the Mak/SCT difference? They were both collimated with the artificial star before my shootout that the Mak won so easily.

 

Astro Foren has a test on a Celestron C9.25 with amazing results, 1/11th wave and Sterhl of 0.98;
http://astro-foren.d...r/?postID=49917
So why is Mak, visually, sharper than any SCT, the answer is very simple, smoothness of figure, If you look at some of the images on the above test, particularly Lyot Test, you will see a very rough surface, the hallmark of all SCT's.
The most important optical quality for high power planetary observation is smoothness of figure, the numbers alone do not give a true picture, and remember, we are talking visual only.

 

Vahe


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#31 Brian Palmer

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Posted 01 November 2015 - 10:11 PM

Your synopsis sounds pretty good .

I think SCTs are better for getting a wider field. Lower power you can fit in some wide nebulaes that the maks just aren't that good for. They generally have a 1.25 inch back and even if added a 2" there are limits with the F15s. It's basically built for higher power things like planets. 

I have two maks.. a 180mm Orion and 127 Orion. The sharpness on terrestrial  viewing vs. the 12" Meade SCT I once had is astonishing. The Meade at 12" can pull in some serious light for deep space but those maks are crazy sharp. Also they have a meniscus lens instead of just mirrors .

If you want a more all around get a SCT. Maks in my eyes are a bit more specialized 


Edited by Brian Palmer, 02 November 2015 - 11:52 AM.

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#32 orion61

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Posted 01 November 2015 - 10:37 PM

So what makes a Maksutov so much sharper than a Schmidt?

 

In a shootout, my 7" Mak easily beat out my 8" SCT. I still like the lighter weight SCT but at these sizes, I can carry either one easily. I had aperture fever and can say that at larger sizes, I don't like to carry any telescope, (but still do).

 

To answer two earlier questions, I am strictly visual. I also spend lots of time collimating. On my 16" Dob, I use a TuBlug and collimate on every object. I use an artificial star for my  Cassegrains.

 

So what is it about the Mak that makes it so good? And in a similar tone, what is it about Dall Kirkhams or iDK's that make them so sensitive to temperature, (or is it that their owners are just that much more sensitive)?

 

Clear skies,

Peter

Maks are usually all Spherical surfaces. The SCT has the complex Schmidt Corrector and Spherical Primary Mirror.

In a nutshell, the Maks are easier to make, but in larger Apertures prone to some Spherical Aberration by nature.

Those Meade 7" Maks (especially the early ones) are superb tubes! Very hard to beat in a similar sized telescope Lunar/Planetary, Double Stars and some DSO's such as Globular clusters and Planetary Nebula! But with mine Uranus was so dim I had a tough time getting enough power out of it. It was amazing the 1" difference the C8 made on it! One inch of size difference will also be a bit less sensitive to seeing as another plus for the Mak.

The only beef I ever had with mine were excessive image shift, I have had 3, and ALL had moderate image shift but worse, was the mirror flop that affected collimation from Horizon to Zenith, and the fork versions had that 8 lb chunk of Cast iron behind the Primary as a counter weight. The ones Meade sold as a stand alone tube did not have the weight in them. Cool down time was a bit longer.

It is amazing what the digital age has done for Astrophotography! Donald Parker co wrote a book about observing and photographing the Solar system with Charles Capin. I nearly wore my copy out. What a dedicated Man and when I met him, was one very nice person.


Edited by orion61, 01 November 2015 - 10:48 PM.


#33 Richard Whalen

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Posted 01 November 2015 - 11:51 PM

The biggest difference between most SCT's and MCT's is optical quality. Most SCT's are massed produced, many MCT's are not. Also the design of the MCT lends itself to be figured easier to a higher level. Add in the fact that many MCT's have a longer focal ratio and a smaller secondary obstruction and it explains why they often leave SCT's in the dust not just on planetary observing, but anything that will fit into their fov.

 

Also the low production MCT's usually have better mechanics, no mirror flop, better focusers than mass produced SCT's. If you compare a mass produced MCT to a SCT, all bets are off....

 

I've looked through and owned several of each, and in my experience finding a really good MCT is more common than a really good SCT, though they can be found. In other words, you tend to get what you pay for unless you are lucky, or unlucky.


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#34 Richard Whalen

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Posted 02 November 2015 - 12:04 AM

As far as Celestron optical quality starting with the Super C8 a word of warning. It took a huge dip with the Super C8 plus that came out the last time Halleys comet came around. A local dealer got 11 of them in as scopes were flying off the shelf with all the media hype. We set them all up in his parking lot and star tested them. 9 of the 11 were not even 1/4 wave, one was just, and one was slightly better .I bought the slightly better one, but ended up selling it within a year to get a 8" f6 Newtonian with better optics.



#35 rmollise

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Posted 02 November 2015 - 09:09 AM

As far as Celestron optical quality starting with the Super C8 a word of warning. It took a huge dip with the Super C8 plus that came out the last time Halleys comet came around. A local dealer got 11 of them in as scopes were flying off the shelf with all the media hype. We set them all up in his parking lot and star tested them. 9 of the 11 were not even 1/4 wave, one was just, and one was slightly better .I bought the slightly better one, but ended up selling it within a year to get a 8" f6 Newtonian with better optics.


Yep, I was fool enough to sell my perfectly good Super C8 to buy a poorer (though not terrible) Super C8 Plus during Halleytime. ;)
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#36 Daniel Mounsey

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Posted 02 November 2015 - 09:20 AM

 

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

Daniel,

 

What's up? When are you going to invite me to speak out west? (brown nosing times 10).....

 

Your post gave me pause to reflect on optical quality as it manifests in observing vs imaging.....basically I probably disagree more than agree with your statement, but it's close....

 

I would differentiate by saying raw aperture overcomes optical quality for planetary imaging over around 8 inches. Meaning the optical quality can slide a bit, but is compensated for by the inherent resolving power gain.

 

My 2 cents...

 

Dan Llewellyn

"The Rodney Dangerfield of Planetary Imaging"

 

 

Dan, I actually agree with you on the aperture too. Anytime you want to visit the west, feel free to drop by. :grin:


Edited by Daniel Mounsey, 02 November 2015 - 09:21 AM.


#37 Jeff B

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Posted 02 November 2015 - 09:22 AM

All of my MCT's have been of really high quality optically and mechanically.  All have been either TEC (6, 7, 8) or Intes (M500, M715, M815, MN5.5, MN56, MN66, MN76, MN86) with one APM MN86 (Intes optics).  Not a stinker in the bunch.

 

Let's not  forget about the Mak-Newts either.  Save for their weight and length in comparison to their stubby brothers, they are hard to beat. 

 

I've a so-so C11, which sits around, and an excellent C14 (Company 7 sourced) which tends to sit around due to its weight.  The SCT's DO have the price advantage though.

 

Jeff



#38 A6Q6

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Posted 02 November 2015 - 01:04 PM

 

The first photo is unprocessed but shows the seeing that night. The second is the same photo  processed with RigiStax 6 . I used a Quantum 6 Mak 33% CO, that I have had since 1978 and an old Orion StarShoot imager III camera.   I would rather observe than image but on a poor night I can get pretty good results imaging because I can stack fleeting moments.   My Mak has never taken a back seat to any SCT in over 35yrs until I got a mint 30yr old Super C8 Plus last summer.  I used to laugh years ago when I read Celestron had 1/10 wave optics. I'm not laughing anymore.  Since this SCT can run with my Mak,(big CO and all) the advantage is 8" vs 6" and it is much lighter than the 6" Mak.  They say Celestron SCTs are lighter than the same size Meade.   I will leave the reflector, both dob and eq mounted to others, although I have a C5 with very good optics that I would take over the wonderful RV-6 that I had years ago because the C5 is sooooo easy to move around.   I don't have any experience with large refractors but I am enjoying a 60mm mounted on my new to me C8 for its low power wide field views. 

Cool.  Could you give some specifics as to the number of frames, percent used, wavelet settings and stuff like that?

Jeff

 

Hi Jeff, check your PM



#39 TG

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Posted 02 November 2015 - 02:37 PM

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

 

This is demonstrably false. Good optics is a necessary but not sufficient condition for good planetary images. So if the images are good, the optics have to be good as well but not vice versa. If this weren't true, seeing would be an irrelevant factor in imaging and that happens to be a necessary condition as well for good images.

 

My personal experience has been that a superb 11 inch aperture produced superb planetary images. A mediocre 11 in aperture produced mediocre ones.

 

There's a lot of nonsense on these forums about how post-processing can compensate for mediocre optics. IME, this simply isn't true.

 

6Cv8wfU.jpg?18Q1uZia.jpg?2

 

 

Tanveer.


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#40 JohnH

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Posted 02 November 2015 - 03:43 PM

 

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

 

This is demonstrably false. Good optics is a necessary but not sufficient condition for good planetary images. So if the images are good, the optics have to be good as well but not vice versa. If this weren't true, seeing would be an irrelevant factor in imaging and that happens to be a necessary condition as well for good images.

 

My personal experience has been that a superb 11 inch aperture produced superb planetary images. A mediocre 11 in aperture produced mediocre ones.

 

There's a lot of nonsense on these forums about how post-processing can compensate for mediocre optics. IME, this simply isn't true.

 

6Cv8wfU.jpg?18Q1uZia.jpg?2

 

 

Tanveer.

 

If you optics are only 1/4 wave, the absulute best your images ever are are 1/4 wave also.

 

Add in distorsion, poor tracking etc and this declines still further.

 

All that stacking does is combine many good images into a brighter image



#41 DesertRat

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Posted 02 November 2015 - 03:58 PM

Tanveer wrote:

My personal experience has been that a superb 11 inch aperture produced superb planetary images. A mediocre 11 in aperture produced mediocre ones.

True, however that is a tautology.  I know its a personal experience, which I dont doubt, and is my experience also.  Evaluation of relative merits is difficult as atmospheric seeing and thermal effects must be accounted for.

 

 

However what Daniel is saying is also true.  In planetary imaging an imperfect optic with sufficient aperture will best a smaller perfect aperture.  Practiced with lucky imaging this holds true in visible wavelengths for apertures up to ~1 meter.

 

JohnH wrote:

All that stacking does is combine many good images into a brighter image

Stacking provides better sampling of small features due to summation and averaging of detail movement.  Here a small amount of seeing actually helps in a natural drizzling mechanism.  And most important the signal to noise is raised by ~sqrt(Nframes) allowing for image processing without raising the noise level too much.

 

 

Glenn



#42 maadscientist

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Posted 02 November 2015 - 04:19 PM

 

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

 

This is demonstrably false. Good optics is a necessary but not sufficient condition for good planetary images. So if the images are good, the optics have to be good as well but not vice versa. If this weren't true, seeing would be an irrelevant factor in imaging and that happens to be a necessary condition as well for good images.

 

My personal experience has been that a superb 11 inch aperture produced superb planetary images. A mediocre 11 in aperture produced mediocre ones.

 

There's a lot of nonsense on these forums about how post-processing can compensate for mediocre optics. IME, this simply isn't true.

 

6Cv8wfU.jpg?18Q1uZia.jpg?2

 

 

Tanveer.

 

 

The big question is: why can a mediocre 10 inch SCT with average optics produce a better planetary image than an almost perfect 5 inch apo? We can talk Stehl ratio all day long, but the encircled energy of a 33% obstructed SCT with 1/8th wave spherical abbertion is only .78. Yet it rules, and going up in aperture, not necessarily quality,  the C14 spanks it.

 

IMHO, the raw resolving power of the increase in aperture shows up in planetary maging. Those additional details might not be resolved perfectly, but they are there....



#43 orion61

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Posted 02 November 2015 - 05:15 PM

 

As far as Celestron optical quality starting with the Super C8 a word of warning. It took a huge dip with the Super C8 plus that came out the last time Halleys comet came around. A local dealer got 11 of them in as scopes were flying off the shelf with all the media hype. We set them all up in his parking lot and star tested them. 9 of the 11 were not even 1/4 wave, one was just, and one was slightly better .I bought the slightly better one, but ended up selling it within a year to get a 8" f6 Newtonian with better optics.


Yep, I was fool enough to sell my perfectly good Super C8 to buy a poorer (though not terrible) Super C8 Plus during Halleytime. ;)

 

YEP me too, I sold my "inferior cheap" Super Polaris C8 for one of those too. Dumb Move as the SP Vixen has become one of the most Classic mounts of all time.....AND most copied. My SC8P had 5 pretty diffraction rings around every Star.

Those dazzling rings sure were pretty tho.



#44 saemark30

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Posted 02 November 2015 - 05:32 PM

The larger Maks will have aspherical surface as does Mewlons but there seems to be no complaints about those.


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#45 Daniel Mounsey

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Posted 03 November 2015 - 01:28 AM

 

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

 

This is demonstrably false. Good optics is a necessary but not sufficient condition for good planetary images. So if the images are good, the optics have to be good as well but not vice versa. If this weren't true, seeing would be an irrelevant factor in imaging and that happens to be a necessary condition as well for good images.

 

My personal experience has been that a superb 11 inch aperture produced superb planetary images. A mediocre 11 in aperture produced mediocre ones.

 

There's a lot of nonsense on these forums about how post-processing can compensate for mediocre optics. IME, this simply isn't true.

 

6Cv8wfU.jpg?18Q1uZia.jpg?2

 

 

Tanveer.

 

 

Tanveer,

 

There are many other shootouts I've not bothered to publish. Here's a few reviews for the OP though. What I'm more interested in is your claim that good optics are needed for planetary imaging.

 

http://www.cloudynig...ry_scopes_1.pdf

 

http://www.cloudynig...ts/shootout.pdf

 

http://doctordreview...0-teleport.html

 

Do you think those images you posted are indicative of great optics? Do you see that detail visually? I'd like an answer to my question because I'm this close to dropping a bombshell on all these planetary imagers once and for all, and I'll do it from my own website.


Edited by Daniel Mounsey, 03 November 2015 - 01:30 AM.

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#46 maadscientist

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Posted 03 November 2015 - 02:51 AM

 

 

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

 

This is demonstrably false. Good optics is a necessary but not sufficient condition for good planetary images. So if the images are good, the optics have to be good as well but not vice versa. If this weren't true, seeing would be an irrelevant factor in imaging and that happens to be a necessary condition as well for good images.

 

My personal experience has been that a superb 11 inch aperture produced superb planetary images. A mediocre 11 in aperture produced mediocre ones.

 

There's a lot of nonsense on these forums about how post-processing can compensate for mediocre optics. IME, this simply isn't true.

 

6Cv8wfU.jpg?18Q1uZia.jpg?2

 

 

Tanveer.

 

If you optics are only 1/4 wave, the absulute best your images ever are are 1/4 wave also.

 

 

1/4 wave is diffraction limited. You can't get detail past the diffraction limit...



#47 maadscientist

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Posted 03 November 2015 - 03:24 AM

 

 

Don was a mentor to many, however, planetary imaging says little to nothing about the optical quality of telescopes. That's nearly all just conditions for good data, a good camera combined with great processing.

 

This is demonstrably false. Good optics is a necessary but not sufficient condition for good planetary images. So if the images are good, the optics have to be good as well but not vice versa. If this weren't true, seeing would be an irrelevant factor in imaging and that happens to be a necessary condition as well for good images.

 

My personal experience has been that a superb 11 inch aperture produced superb planetary images. A mediocre 11 in aperture produced mediocre ones.

 

There's a lot of nonsense on these forums about how post-processing can compensate for mediocre optics. IME, this simply isn't true.

 

6Cv8wfU.jpg?18Q1uZia.jpg?2

 

 

Tanveer.

 

 

Tanveer,

 

There are many other shootouts I've not bothered to publish. Here's a few reviews for the OP though. What I'm more interested in is your claim that good optics are needed for planetary imaging.

 

http://www.cloudynig...ry_scopes_1.pdf

 

http://www.cloudynig...ts/shootout.pdf

 

http://doctordreview...0-teleport.html

 

Do you think those images you posted are indicative of great optics? Do you see that detail visually? I'd like an answer to my question because I'm this close to dropping a bombshell on all these planetary imagers once and for all, and I'll do it from my own website.

 

Daniel, I just notice "you" were the Doctor D....how about that.

 

When I planetary image, the video stream capture is constantly being distorted, giving momentary glimpses of sharp images, but mostly rather soft and semi-blurry, and geometrically distorted...There is no doubt the detail is ferreted out later when the bad frames are discarded and some strong algorithms are used (wavelets, etc...). When seeing is good and stable, I do get a nice visual at the eyepiece of my C14, but no where near the stacked and manipulated final planetary image. I am of the opinion that the video stream used during planetary imaging will capture fleeting moments of diffraction limited seeing (1/4 wave), and enough of this stacked with the bad discarded, can produce detail near the theoretical resolving power of the scope. This is basically a similar result to adaptive optics, maybe turned 90 degrees. Increased resolution from adaptive optics is based on countering the seeing, lucky imaging on keeping the precious few clear ones that come through....

 

In both instances, the goal is to push through the atmospheric limit and get nearer to the Raleigh Criterion of theoretical resolving limit. This produces more detail...sharp detail? contrasty? maybe not, but maybe not necessary as just having crossed the threshold of more detail in sum produces a better image for the web...Since we are pushing through the atmosphere, I tend to agree with you, all you can say with 11, 12, 14, 16 aperture scopes is they are performing close or at the 1/4 wave diffraction limit...

 

BTW, for everyone reading this, the Hubble Space Telescope is no more than 90 strehl in red and 80 strehl in blue, 1/5 and 1/4 wave respectively...



#48 PowellAstro

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Posted 03 November 2015 - 06:36 AM

A 1/4 wave instrument is only good if there is no turbulence and zero tube currents. Any outside influences with a 1/4 wave instrument throws additional light outside the airy disk. With a 1/16 wave instrument, it is much more stable under the same conditions. So for example, say we have 1/4 wave tube currents and 1/8 wave seeing:

The 1/4 wave instrument is now acting as if the mirrors has almost a full wave error.

The 1/16 wave instrument is still diffraction limited. All the energy is still within the airy disk.

1/4 wave is fine for the Hubble as it is free from the wavefront damaging seeing as well as a lot of the thermal conditions we deal with.

Edited by PowellAstro, 03 November 2015 - 06:38 AM.

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#49 Jon Isaacs

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Posted 03 November 2015 - 07:53 AM

What about color correction? Why is it a refractor thing?

 

Since the light doesn't pass through glass, a Newtonian would be perfect. But it does have glass in the eyepiece.

 

SCT's and MCT's don't seem to have it but the light enters through glass. In the case of the MCT, the light enters at an angle that looks greater than in a refractor.

 

I had a 110mm Orion "Apo" refractor and on Venus it had a strong violet halo that I've not seen in my Cassegrains. 

 

Clear skies,

Peter

 

Peter:

 

Your Orion 110mm "apo" was a large aperture, fast, ED doublet based on FPL-51 rather than the FPL-53..  While Orion was happy to call it an apochromat, most would call it border line and certainly not free from chromatic aberration.  At that aperture and focal ratio, one would want the better glass and maybe even a triplet.  Rest assured that there are refractors that are color free on Venus.  

 

Jon 


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#50 Jon Isaacs

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Posted 03 November 2015 - 08:02 AM

 

 

The big question is: why can a mediocre 10 inch SCT with average optics produce a better planetary image than an almost perfect 5 inch apo? We can talk Stehl ratio all day long, but the encircled energy of a 33% obstructed SCT with 1/8th wave spherical abbertion is only .78. Yet it rules, and going up in aperture, not necessarily quality,  the C14 spanks it.

IMHO, the raw resolving power of the increase in aperture shows up in planetary maging. Those additional details might not be resolved perfectly, but they are there....

 

It is not really a big question, the answer is in the scale which comes from the aperture.  Strehl ratio is measured relative to the aperture, a perfect 5 inch scope encircles all the energy possible with a 5 inch telescope.   But on an absolute scale, if it were judged on identical angular scale as a 10 inch scope, the Strehl would be not good at all.   When one considers that the first diffraction ring of a 10 inch is approximately the angular size of the spurious disk of a 5 inch refractor, on an absolute scale, the 10 inch, even though it has a large CO, concentrates the light better which equates to better fine scale contrast.   

 

Jon


  • Asbytec, orion61, jjack's and 1 other like this


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