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1 inch APO vs 12 inch SCT

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#126 SandyHouTex

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Posted 04 January 2018 - 10:13 AM

 

The is no such thing as "never".  If properly made with high quality optics, and then properly collimated, an 8 inch SCT will beat a 6 inch APO all the time in similar atmospheric conditions.

 

 

 

Unless of course you believe the physics of optics are incorrect.

 

In my experience (visual observing), this is simply not true, if we are talking about bog standard, run-of-the-mill 8" SCT's, no matter how excellent their optics are. The 6" refractor (it doesn't have to be an apochromat) will be FAR less sensitive to thermal issues than the 8" SCT and so under many observing conditions, especially in rapidly falling temperatures, which we often see where I live, the refractor will easily outperform the SCT, simply because it can track the temperature better. On a few nights each year, the SCT will be able to show its superior resolution, but generally the refractor will show better planetary images. On deep-sky, the results will be more mixed and depend on the object type. On large galaxies and nebulae, the refractor could be better, while the SCT would have the upper hand on small galaxies. 

 

When we are discussion the merits of different designs, we simply can't use the theoretical performance to much at all, as it is how the scope performs under real world conditions that counts. People, and especially commercial telescope designers, tend to forget that. 

 

 

Clear skies!
Thomas, Denmark

 

Why would you compare an APO that costs 10X as much, to a "...bog standard, run-of-the-mill 8" SCT,...".  And I'm confused when you follow it up with "..., no matter how excellent their optics are."  I would expect the first quote excludes the second.  If an SCT has excellent optics, how can it be a run of the mill SCT?


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#127 Astrojensen

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Posted 04 January 2018 - 10:43 AM

 

 

The is no such thing as "never".  If properly made with high quality optics, and then properly collimated, an 8 inch SCT will beat a 6 inch APO all the time in similar atmospheric conditions.

 

 

 

Unless of course you believe the physics of optics are incorrect.

 

In my experience (visual observing), this is simply not true, if we are talking about bog standard, run-of-the-mill 8" SCT's, no matter how excellent their optics are. The 6" refractor (it doesn't have to be an apochromat) will be FAR less sensitive to thermal issues than the 8" SCT and so under many observing conditions, especially in rapidly falling temperatures, which we often see where I live, the refractor will easily outperform the SCT, simply because it can track the temperature better. On a few nights each year, the SCT will be able to show its superior resolution, but generally the refractor will show better planetary images. On deep-sky, the results will be more mixed and depend on the object type. On large galaxies and nebulae, the refractor could be better, while the SCT would have the upper hand on small galaxies. 

 

When we are discussion the merits of different designs, we simply can't use the theoretical performance to much at all, as it is how the scope performs under real world conditions that counts. People, and especially commercial telescope designers, tend to forget that. 

 

 

Clear skies!
Thomas, Denmark

 

Why would you compare an APO that costs 10X as much, to a "...bog standard, run-of-the-mill 8" SCT,...".  And I'm confused when you follow it up with "..., no matter how excellent their optics are."  I would expect the first quote excludes the second.  If an SCT has excellent optics, how can it be a run of the mill SCT?

 

Sorry, I was unclear. My bad. When I was talking about "bog standard SCT's" I was thinking about their mechanical and thermal design, not so much about the optics, which is why the sentence seemed to be contradictory. 

 

Again, sorry about the confusion.

 

 

Clear skies!
Thomas, Denmark


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#128 BillP

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Posted 04 January 2018 - 11:29 AM

I've never bought into this. They're both closed tube designs with very similar materials in use. It seems to me that the primary variables would then be weight (thermal mass), volume, surface area etc. Of those, I'd say Cassegrains get dinged the most by low surface area compared to the long, skinny tubes of refractors. With the same aperture, the surface area per volume should be the same and I would expect them to cool at the same rate. But of course, we are usually comparing a much larger CAT to a smaller refractor.

 

An explanation I give more credence to is that it's seeing-related. The idea is that larger apertures are more vulnerable to poor seeing, and Cassegrains also operate at inherently higher magnifications than refractors due to their very different focal lengths. This high magnification also magnifies the effects of poor seeing and thermal air currents. This is consistent with my experience - whenever I have noted exceptionally clean, crisp images of stars or anything else, it was at an exceptionally low magnification - usually, with my 40mm eyepiece.

 

I agree that from a conceptual standpoint it is easy to get swayed one way or the other as to what is going on.  However, when things like this are easily testable, I will usually conduct some personal tests to give myself a better idea of what may be going on and then learn how to better utilize the equipment.  So in the cool down arena I had many times taken both my 6" f/8 Apo out with my 8" f/10 SCT.  On one of those evenings the SCT actually reached and maintained equillibrium.  It was fantastic as the other several hundred evenings it never occurred.  Both scopes were delivering fantastically etched views of Saturn.  6" Apo showed the slightest bit of a richer saturation to the colors on Saturn, but that was it.  Moving to Globulars after that the larger aperture SCT showed it could go just a little deeper.

 

Now on the other gazillion nights out together, the Apo cooled and provided rock steady views with well formed airy disks that had stable diffraction rings on noghts of good seeing.  On those same evenings, the SCT would show its classic wooly star with messy airy disks.  So that pretty much demonstrated that the issue was nothing to do with the seeing.  For many months after that I would routinely take out my 80mm Apo with whatever primary scope I was taking out and use that as my seeing-stability reference scope.  And sure enough that proved very benefitial because since that size and design cools very rapidly, always easy to see what the seeing actually is.  So on nights where the planetary was not working well on the larger scope just went to the smaller one to guage the steadiness of the airy disk in the area I was observing.  When it was steady and the view was not from the larger scope, like the larger Apo, I knew with a little patience it would cool completely so I could then turn to planetary later in the evening.  That always worked.  Then on nights when the reference scope was showing poor seeing, that would play out also as the larger scope would never achieve perfect views as one can expect when the seeing is not best for planetary.

 

As far as a smaller aperture being able to "punch through" seeing better...that is all fantasy IMO.  There is no way in the atmosphere that there are consistent thermal cells extending from ground all the way through that just happen to be in perfectly straight lines from your scope to target, or non-moving columns of air.  That is just the silliest thing I have ever heard.  Any weather professional or pilot knows differently!


Edited by BillP, 04 January 2018 - 11:33 AM.

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#129 rmollise

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Posted 04 January 2018 - 01:21 PM

As a comment upon this part of Daniel's post, I, too often wonder about people looking at the same objects over and over. In my case, I have some observing goals, initially the Messiers, then the Herschel 400, now an amalgam of objects culled from various deep sky lists I have acquired. I am just getting started on double stars (only have observed a couple of hundred or so) and the challenge of splitting doubles is really fun. I like goals. It keeps things fresh for me and is always sharpening my observing skills, which include getting to know the limitations of my equipment.
 
I always check a few of my favorite M-objects, as they are my friends, and have observed them enough to use them to rather easily get a read on the observing conditions for the night. I also use the M-objects to check out a new eyepiece, filter, or new scope.
 
Lots of objects up there. Thankfully, I'll never get them all.
 
Arizona Ken

​Why do people look at the same objects over and over? Because they love them. That's why I'll look at M13 and M42 anytime they are in the sky. Why would you look at the Mona Lisa over and over?

 

Oh, I've done the Herschel 2500, the Arps, counted PGCs, etc., etc. But at this time in my astronomy career, it appears I've been drawn back to the beautiful things that suckered me in in the first place. The greatest rule in amateur astronomy? There are no rules as to how you must enjoy it. :)


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#130 treadmarks

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Posted 04 January 2018 - 01:56 PM

 

As a comment upon this part of Daniel's post, I, too often wonder about people looking at the same objects over and over. In my case, I have some observing goals, initially the Messiers, then the Herschel 400, now an amalgam of objects culled from various deep sky lists I have acquired. I am just getting started on double stars (only have observed a couple of hundred or so) and the challenge of splitting doubles is really fun. I like goals. It keeps things fresh for me and is always sharpening my observing skills, which include getting to know the limitations of my equipment.
 
I always check a few of my favorite M-objects, as they are my friends, and have observed them enough to use them to rather easily get a read on the observing conditions for the night. I also use the M-objects to check out a new eyepiece, filter, or new scope.
 
Lots of objects up there. Thankfully, I'll never get them all.
 
Arizona Ken

​Why do people look at the same objects over and over? Because they love them. That's why I'll look at M13 and M42 anytime they are in the sky. Why would you look at the Mona Lisa over and over?

 

Oh, I've done the Herschel 2500, the Arps, counted PGCs, etc., etc. But at this time in my astronomy career, it appears I've been drawn back to the beautiful things that suckered me in in the first place. The greatest rule in amateur astronomy? There are no rules as to how you must enjoy it. smile.gif

 

I feel like we are neglecting the important questions. If there are alien astronomical societies out there, would the Milky Way make one of their "best of" lists? I like to think so. Or do they consider our entire galaxy nothing more than 5 minutes they'll never get back? And what about our Sun? It's not a double, not in a nebula, and it's not part of a cluster. The best we could hope for is to be part of some constellation. We're totally boring.... No wonder aliens haven't noticed us.


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#131 Mitrovarr

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Posted 04 January 2018 - 02:21 PM


As a comment upon this part of Daniel's post, I, too often wonder about people looking at the same objects over and over. In my case, I have some observing goals, initially the Messiers, then the Herschel 400, now an amalgam of objects culled from various deep sky lists I have acquired. I am just getting started on double stars (only have observed a couple of hundred or so) and the challenge of splitting doubles is really fun. I like goals. It keeps things fresh for me and is always sharpening my observing skills, which include getting to know the limitations of my equipment.

I always check a few of my favorite M-objects, as they are my friends, and have observed them enough to use them to rather easily get a read on the observing conditions for the night. I also use the M-objects to check out a new eyepiece, filter, or new scope.

Lots of objects up there. Thankfully, I'll never get them all.

Arizona Ken

​Why do people look at the same objects over and over? Because they love them. That's why I'll look at M13 and M42 anytime they are in the sky. Why would you look at the Mona Lisa over and over?

Oh, I've done the Herschel 2500, the Arps, counted PGCs, etc., etc. But at this time in my astronomy career, it appears I've been drawn back to the beautiful things that suckered me in in the first place. The greatest rule in amateur astronomy? There are no rules as to how you must enjoy it. smile.gif
I feel like we are neglecting the important questions. If there are alien astronomical societies out there, would the Milky Way make one of their "best of" lists? I like to think so. Or do they consider our entire galaxy nothing more than 5 minutes they'll never get back? And what about our Sun? It's not a double, not in a nebula, and it's not part of a cluster. The best we could hope for is to be part of some constellation. We're totally boring.... No wonder aliens haven't noticed us.

I would assume it would depend on location. If there are alien astronomers in Andromeda or Triangulum (or, even better, in one of the Magellanic clouds), the Milky Way is probably pretty awesome. Get further away and it would gradually recede in importance until is is invisible altogether.

The Sun is probably only of interest to aliens on a very few very near stars. Given the generally low odds that any of them have intelligent life right now, I would guess that nobody except humans takes any notice of Sol.

#132 Jared

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Posted 04 January 2018 - 06:38 PM

Yes I’m exaggerating lol.gif   but why is this a thing in so many refractor discussions on the web?

Why is It that so many will do a comparison of a 4 inch APO and an 8 inch SCT or Newtonian and think that they see more in the APO? Limiting magnitude and resolution will surely be better in the larger scope. Am I missing something?

Why do they do the comparison?  Easy.  They have decided to spend their money on a smaller, hopefully high quality scope rather than a larger, perhaps lower quality scope, and they want to know whether they are making a wise choice.  Hence, the comparison.  Nobody buying a high quality 4" refractor is thinking, "Should I get the Takahashi FC-100DL or will the Celestron ExploraScope 114 meet my needs equally well?"  They are similar in light grasp and resolution, but no experienced observer actually struggles making a decision between these two.  But, compare that FC-100DL to an 8" Edge HD, and suddenly you are in the same ballpark in terms of cost (depending on the mount you select for each, of course).  This is something that a reasonable, experienced observer might well debate, and either scope could be a reasonable answer depending on one's typical seeing conditions, available time for observing, convenience requirements, the objects one likes to view, willingness to performance maintenance tasks like collimation, etc.  And, no, it doesn't require that a smaller scope be able to "break the laws of physics" and out-resolve a significantly larger scope in order for one to prefer the views in the smaller refractor.  My 5" refractor does not, can not, and will not out-resolve a decent or better 8" reflector under most conditions.  I wouldn't expect it to--too big a gap in aperture.  It doesn't have the light grasp of an 8" reflector under any observing conditions.  But I still prefer its capabilities to those of any 8" reflector.  

 

Look at it this way... That same 5" refractor when coupled to a CCD camera will easily and consistently show me dimmer objects with much greater detail than any 8" or 10" reflector with an eyepiece.  So why would I ever choose visual astronomy?  I can't see as much when I am observing visually, so clearly astrophotography is better, yes?  Vastly more resolution and light grasp with a CCD than with my very mediocre scotopic vision, regardless of the aperture.

 

How often have you seen the bridge of stars, gas, and dust connecting M51 to NGC 5195 with your 8"-10" reflector?  Be honest now.  What about the 15th magnitude central star in the Ring Nebula?  How often do you see that with an 8" SCT?  I can get more details on M51 or the Ring Nebula--and color data at that--in a single five minute exposure with a 5" scope under my urban sky conditions than any visual observer will ever see with a 8" or 10" scope from the darkest of dark sky sites.  And yet, lots of people prefer visual observing to astrophotography.  Some want the simplicity of visual observing. For some, they like the visceral nature of looking at the actual photons rather than a reconstruction of them on a computer screen. Some prefer the challenge of the physical observation over the challenge of the computer processing.  Neither observing approach is any more "right" or any more "true."  

 

By the same token, I think it's silly for owners of 8" reflectors to say they are intrinsically "better" than 4" refractors.  Better for what?  What do you want or expect to see?  Under what sky conditions?  Just as it's silly for refractor owners to say their smaller scopes are clearly "better" than a larger reflector.  Better for what objects?  After how much cooling time?  Under what kind of skies?  We all have slightly different observing goals and are excited by different objects and different challenges.  Some people enjoy spending an hour or more on M13 trying to take it all in, while others would rather check it off of their observing list and move on to something more "challenging".  The reasons for the comparison are pretty straightforward--similar budgets with very different strengths and weaknesses, so lots of people want to compare.  The competition between reflector and refractor owners, though, is kind of silly. Pick what's right for you, for your budget, for your location, for the objects you like to look at and get out under the stars.  Me?  I generally prefer astrophotography over visual because I can see so much more, but that doesn't make my choices any better or worse than someone working to complete the Herschel 400 with their 12" Dob.


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#133 Asbytec

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Posted 05 January 2018 - 07:40 AM

 

So, while the physics cannot be argued, certainly the sharpness of the image can, and that's where the refractorians will gladly chime in.

 

 

So there I am with my 120 mm ED/apo and my 10 inch F/5, $240 on Astromart both pointed at at an 0.83" double..  The 10 inch is of course cooled with a fan and properly collimated. The seeing is excellent.. 

 

The 120 mm provides a slightly elongated star image.  The 10 inch makes a clean split. 

 

It takes a careful eye to see the slight elongation.  A refractor fan might say the refractor was sharper,  I say no way Jose. It's not sharper..  It's duller..  Unable to resolve the image.  

 

The same is true viewing the planets..  Viewing globulars..  How can it be sharper,  you can't resolve it? 

 

Jon

 

Jon, I had that question and posed it to a 6" APO user. I wanted to know what he could see that my 6" Cat could not. He mentioned some lunar hills on the limb. Fine, I've seen them, too. His description 'sounded" like his contrast was slightly better. His darks we slightly darker. That kind of thing. True or not, I've always wondered what being "sharper" meant. I think this is what it means. We both saw the same scene, just his was (apparently), well, a bit cleaner as he implied in his description of the same thing I saw. 

 

Jared,

 

"So why would I ever choose visual astronomy?"

 

 

Well, visual (I'm sure you know well) is a different animal. It's man doing the observing and reaping the reward for what he can see without the aid of electronics and processing software. Even if it's nowhere near as much. It's a more personal endeavor in ways imaging is not. And please do not take my comment as a swipe at imagers, it's not. There are plenty of guys making some beautiful images with challenges involved that create reward. So, it's also beautiful and rewarding, but visual is more personal. You might agree, but that's why I choose visual observing - me against the odds. Often rewarded nicely even if I cannot see the entire spiral structure of a faint galaxy. I saw what I saw by the sweat of my brow, and that is where I derive pleasure. 

 

...so lots of people want to compare.

 

You know, if people want to compare, maybe we should compare what we see instead of numbers, stats, and price. In a comparison thread, I'll often post a sketch of what I see hoping someone will show me the same...so we can get a virtual look through each other's scopes and eye/brain system. Maybe that is what matters, really. 


Edited by Asbytec, 05 January 2018 - 08:56 AM.

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#134 Daniel Mounsey

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Posted 05 January 2018 - 08:52 AM

 

To put it into perspective: Rik joined me for a long observing session with my Tak FS102NSV. He was amazed at it's views and started to get serious about high-end apo doublets for high power visual use. Mirror man as he is.

 

SCT's, Mak's or Newt's that are made to perfection are fantastic performers. From 2"-7", per aperture, they will never beat a high-end apo. But they are limited in aperture due to size, weight and cost,  more so with a stable driven mount. Then at about 8", we enter a turning point. Refractors now enter a territory where their well known advantages start to become less pronounced, disadvantages become more apparent and gradually the mirror scopes come into play. In the 10" size, I prefer a high-end Mak, in the 16" size a top quality Newt. But in 2"-6" the image quality at any power of a high-end refractor rules. And each shows a different sky to the observer.

The is no such thing as "never".  If properly made with high quality optics, and then properly collimated, an 8 inch SCT will beat a 6 inch APO all the time in similar atmospheric conditions.

 

Unless of course you believe the physics of optics are incorrect.

 

.

Sandy,
I don't entirely disagree with you here in some specific ways, but you certainly sound overly optimistic and most of your arguments are merely hypothetical. Do you have something hands-on you'd like to share? I certainly can.


Edited by Daniel Mounsey, 05 January 2018 - 09:00 AM.


#135 bobhen

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Posted 05 January 2018 - 09:10 AM

 

.... Telescopes don't need hundreds of thousands of objects. All they need is a hand controller that has GPS with M13, M42, and M31 on the handset. I have sold thousands of telescopes. When these people come to my star parties, they're all just looking at the same thing over and over every month. They don't grow and they don't realize there's other wonderful objects outside the Messier catalog that look amazing in all sorts of apertures, even small ones. The Messier catalog is like a crutch for these people. I'd like to remove the Messier objects from the night sky for a few days and see how long they last. They'd be closing shop and heading home for good. I'd say.... Hey! but what about that all those hundreds of thousands of objects in the database you wanted? Don't you want to see those? Naaahhhh I just want to see bright showpieces all night. 

 

As a comment upon this part of Daniel's post, I, too often wonder about people looking at the same objects over and over. In my case, I have some observing goals, initially the Messiers, then the Herschel 400, now an amalgam of objects culled from various deep sky lists I have acquired. I am just getting started on double stars (only have observed a couple of hundred or so) and the challenge of splitting doubles is really fun. I like goals. It keeps things fresh for me and is always sharpening my observing skills, which include getting to know the limitations of my equipment.

 

I always check a few of my favorite M-objects, as they are my friends, and have observed them enough to use them to rather easily get a read on the observing conditions for the night. I also use the M-objects to check out a new eyepiece, filter, or new scope.

 

Lots of objects up there. Thankfully, I'll never get them all.

 

Arizona Ken

 

Why do people look at the same object over and over?

 

For the same reasons one revisits and can get lost in seeing the Grand Canyon or Monet’s Water Lilies or the Great Orion Nebula. And although these objects don’t change that much, what we bring and come away with after each observation can change.

 

What would be the point of spending 10 minutes at the rim of the Grand Canyon or in the Metropolitan Museum of Art?

 

In the act of observing, it is our perspective that changes. The objects change us.

 

Bob


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#136 Asbytec

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Posted 05 January 2018 - 09:18 AM

Well, we should look at new objects, too. Go deeper, see what's out there to be seen at the edge of our imagination. A 12" SCT can show you things a 1" APO (exaggerating, too) simply cannot. But, yea, I've seen M13 so many times (we all have, surely). It's always a pleasure to hit it from time to time. Kinda nostalgic, really, ole M13 is. And with experience, M33 is not as featureless as we might have believed. There's a whole universe out there, find a globular that is not as easy to resolve and have fun with it. See if you can pick out a light scattering of few barely visible stars. Fun!


Edited by Asbytec, 05 January 2018 - 09:21 AM.

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#137 SandyHouTex

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Posted 05 January 2018 - 09:51 AM

 

I've never bought into this. They're both closed tube designs with very similar materials in use. It seems to me that the primary variables would then be weight (thermal mass), volume, surface area etc. Of those, I'd say Cassegrains get dinged the most by low surface area compared to the long, skinny tubes of refractors. With the same aperture, the surface area per volume should be the same and I would expect them to cool at the same rate. But of course, we are usually comparing a much larger CAT to a smaller refractor.

 

An explanation I give more credence to is that it's seeing-related. The idea is that larger apertures are more vulnerable to poor seeing, and Cassegrains also operate at inherently higher magnifications than refractors due to their very different focal lengths. This high magnification also magnifies the effects of poor seeing and thermal air currents. This is consistent with my experience - whenever I have noted exceptionally clean, crisp images of stars or anything else, it was at an exceptionally low magnification - usually, with my 40mm eyepiece.

 

I agree that from a conceptual standpoint it is easy to get swayed one way or the other as to what is going on.  However, when things like this are easily testable, I will usually conduct some personal tests to give myself a better idea of what may be going on and then learn how to better utilize the equipment.  So in the cool down arena I had many times taken both my 6" f/8 Apo out with my 8" f/10 SCT.  On one of those evenings the SCT actually reached and maintained equillibrium.  It was fantastic as the other several hundred evenings it never occurred.  Both scopes were delivering fantastically etched views of Saturn.  6" Apo showed the slightest bit of a richer saturation to the colors on Saturn, but that was it.  Moving to Globulars after that the larger aperture SCT showed it could go just a little deeper.

 

Now on the other gazillion nights out together, the Apo cooled and provided rock steady views with well formed airy disks that had stable diffraction rings on noghts of good seeing.  On those same evenings, the SCT would show its classic wooly star with messy airy disks.  So that pretty much demonstrated that the issue was nothing to do with the seeing.  For many months after that I would routinely take out my 80mm Apo with whatever primary scope I was taking out and use that as my seeing-stability reference scope.  And sure enough that proved very benefitial because since that size and design cools very rapidly, always easy to see what the seeing actually is.  So on nights where the planetary was not working well on the larger scope just went to the smaller one to guage the steadiness of the airy disk in the area I was observing.  When it was steady and the view was not from the larger scope, like the larger Apo, I knew with a little patience it would cool completely so I could then turn to planetary later in the evening.  That always worked.  Then on nights when the reference scope was showing poor seeing, that would play out also as the larger scope would never achieve perfect views as one can expect when the seeing is not best for planetary.

 

As far as a smaller aperture being able to "punch through" seeing better...that is all fantasy IMO.  There is no way in the atmosphere that there are consistent thermal cells extending from ground all the way through that just happen to be in perfectly straight lines from your scope to target, or non-moving columns of air.  That is just the silliest thing I have ever heard.  Any weather professional or pilot knows differently!

 

An excellent post.  I agree with everything you said.



#138 Jon Isaacs

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Posted 05 January 2018 - 09:56 AM

 

 

.... Telescopes don't need hundreds of thousands of objects. All they need is a hand controller that has GPS with M13, M42, and M31 on the handset. I have sold thousands of telescopes. When these people come to my star parties, they're all just looking at the same thing over and over every month. They don't grow and they don't realize there's other wonderful objects outside the Messier catalog that look amazing in all sorts of apertures, even small ones. The Messier catalog is like a crutch for these people. I'd like to remove the Messier objects from the night sky for a few days and see how long they last. They'd be closing shop and heading home for good. I'd say.... Hey! but what about that all those hundreds of thousands of objects in the database you wanted? Don't you want to see those? Naaahhhh I just want to see bright showpieces all night. 

 

As a comment upon this part of Daniel's post, I, too often wonder about people looking at the same objects over and over. In my case, I have some observing goals, initially the Messiers, then the Herschel 400, now an amalgam of objects culled from various deep sky lists I have acquired. I am just getting started on double stars (only have observed a couple of hundred or so) and the challenge of splitting doubles is really fun. I like goals. It keeps things fresh for me and is always sharpening my observing skills, which include getting to know the limitations of my equipment.

 

I always check a few of my favorite M-objects, as they are my friends, and have observed them enough to use them to rather easily get a read on the observing conditions for the night. I also use the M-objects to check out a new eyepiece, filter, or new scope.

 

Lots of objects up there. Thankfully, I'll never get them all.

 

Arizona Ken

 

Why do people look at the same object over and over?

 

For the same reasons one revisits and can get lost in seeing the Grand Canyon or Monet’s Water Lilies or the Great Orion Nebula. And although these objects don’t change that much, what we bring and come away with after each observation can change.

 

What would be the point of spending 10 minutes at the rim of the Grand Canyon or in the Metropolitan Museum of Art?

 

In the act of observing, it is our perspective that changes. The objects change us.

 

Bob

 

 

 

From Arizona Ken's signature:

 

"Considered as a collector of rare and precious things, the amateur astronomer has a great advantage over amateurs in other fields ... the amateur astronomer has access at all times to the original objects of his study; the masterworks of the heavens belong to him as much as to the great observatories of the world. And there is no privilege like that of being allowed to stand in the presence of the original."

--Robert Burnham Jr, Burnham's Celestial HandbookHandbook

 

Jon


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#139 SandyHouTex

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Posted 05 January 2018 - 10:05 AM

 

 

To put it into perspective: Rik joined me for a long observing session with my Tak FS102NSV. He was amazed at it's views and started to get serious about high-end apo doublets for high power visual use. Mirror man as he is.

 

SCT's, Mak's or Newt's that are made to perfection are fantastic performers. From 2"-7", per aperture, they will never beat a high-end apo. But they are limited in aperture due to size, weight and cost,  more so with a stable driven mount. Then at about 8", we enter a turning point. Refractors now enter a territory where their well known advantages start to become less pronounced, disadvantages become more apparent and gradually the mirror scopes come into play. In the 10" size, I prefer a high-end Mak, in the 16" size a top quality Newt. But in 2"-6" the image quality at any power of a high-end refractor rules. And each shows a different sky to the observer.

The is no such thing as "never".  If properly made with high quality optics, and then properly collimated, an 8 inch SCT will beat a 6 inch APO all the time in similar atmospheric conditions.

 

Unless of course you believe the physics of optics are incorrect.

 

.

Sandy,
I don't entirely disagree with you here in some specific ways, but you certainly sound overly optimistic and most of your arguments are merely hypothetical. Do you have something hands-on you'd like to share? I certainly can.

 

Sure.  If you look at my signature, you see that I own every SCT non-EdgeHD Celestron has made, along with a few Maks.  If I'm going to use one, I take it out as the sun is setting and let it sit for a couple hours to aclimate.  Here in Texas, during the warmer months, it doesn't make much sense to try and view things right away, when all of the houses and their roofs are sending up thermals from the heat of the day.  So after a couple of hours I go out and everything is fine.  The seeing south of Houston and near the Gulf of Mexico is almost always exceptional.  If it's really cold, I still set my Cats out for about 2 hours to equilibriate.

 

When I bought my scopes, I immediately did a star test, and the all them are 1/6 wave or better according to Suiter's book.  I send them back for a new one if they are worse than 1/4 wave.  I then make sure they are collimated.  So the optics range from pretty good to excellent.  Given all of that, I don't really have issues with bloated stars.  I think thermal issues, if your using a catadioptric telescope, are to blame for many of the criticisms we read and hear about.

 

Funny thing is, I have heard about similar, what I believe are thermal issues, with the TOA Taks.  Evidently the 3 elements are pretty widely spaced slowing the acclimation of what is certainly a fine refractor.


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#140 Daniel Mounsey

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Posted 05 January 2018 - 10:30 AM

 

 

.... Telescopes don't need hundreds of thousands of objects. All they need is a hand controller that has GPS with M13, M42, and M31 on the handset. I have sold thousands of telescopes. When these people come to my star parties, they're all just looking at the same thing over and over every month. They don't grow and they don't realize there's other wonderful objects outside the Messier catalog that look amazing in all sorts of apertures, even small ones. The Messier catalog is like a crutch for these people. I'd like to remove the Messier objects from the night sky for a few days and see how long they last. They'd be closing shop and heading home for good. I'd say.... Hey! but what about that all those hundreds of thousands of objects in the database you wanted? Don't you want to see those? Naaahhhh I just want to see bright showpieces all night. 

 

As a comment upon this part of Daniel's post, I, too often wonder about people looking at the same objects over and over. In my case, I have some observing goals, initially the Messiers, then the Herschel 400, now an amalgam of objects culled from various deep sky lists I have acquired. I am just getting started on double stars (only have observed a couple of hundred or so) and the challenge of splitting doubles is really fun. I like goals. It keeps things fresh for me and is always sharpening my observing skills, which include getting to know the limitations of my equipment.

 

I always check a few of my favorite M-objects, as they are my friends, and have observed them enough to use them to rather easily get a read on the observing conditions for the night. I also use the M-objects to check out a new eyepiece, filter, or new scope.

 

Lots of objects up there. Thankfully, I'll never get them all.

 

Arizona Ken

 

Why do people look at the same object over and over?

 

For the same reasons one revisits and can get lost in seeing the Grand Canyon or Monet’s Water Lilies or the Great Orion Nebula. And although these objects don’t change that much, what we bring and come away with after each observation can change.

 

What would be the point of spending 10 minutes at the rim of the Grand Canyon or in the Metropolitan Museum of Art?

 

In the act of observing, it is our perspective that changes. The objects change us.

 

Bob

 

 

I too enjoy going back to showpieces and still do. What I was referring to were people who really don't observe anything else but a few showpieces. In other words, they don't grow or learn that there are other objects of fascinating interest. 


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#141 Erik Bakker

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Posted 05 January 2018 - 11:10 AM


So thermal issues are no reason anymore to place an APO refractor above a super high quality SCT.
 

I don't know of any super high quality readily available SCT, especially in a 16".

In mass produced SCT's there are none IMHO. Regardless of aperture. Good for the money? Some. But super high quality? None. 

Super high quality APO/s up to 6" are readily available, their culprit being the lack of bigger sizes and a hefty price per inch of aperture of course. There are very few high quality SCT's and Mak's available between 3.5" and 12", most are NLA new, all are scarce and expensive. And per inch of aperture, none reach the cleanliness of the Airydisk under even the best conditions of the same or somewhat smaller aperture high end APO that I have seen. 



#142 yellobeard

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Posted 05 January 2018 - 11:43 AM

You are right Erik, of course I know that most people are forced to accept the quality that is commercially aviable.
In my 40 years of experience especially with SCT's, I only saw a very few that had exellent optics. They are a very very rare breed indeed, and even when you find one, you still need to do some extra (insulation) work to make them as stable as a high quality apochromatic refractor.

Edited by yellobeard, 05 January 2018 - 11:44 AM.

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#143 Erik Bakker

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Posted 05 January 2018 - 12:15 PM

Much can be done to improve the stability of the images in SCT and Mak telescopes under falling temperatures and I applaud those who try their best to find good solutions for this. 


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#144 azure1961p

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Posted 05 January 2018 - 12:29 PM

Yes I’m exaggerating lol.gif   but why is this a thing in so many refractor discussions on the web?

Why is It that so many will do a comparison of a 4 inch APO and an 8 inch SCT or Newtonian and think that they see more in the APO? Limiting magnitude and resolution will surely be better in the larger scope. Am I missing something?

Provided it's good quality...

 

 

It's like this:

 

1. The apo will provide the absolute best image for it's aperture.  There's no other design that can match it's performance inch for inch . Therefore it can APPEAR to show more than it's size should. In reality it's merely maximized it's full aperture potential.  Other designs do not fulfill their potential as well.

 

2. Apertures APO's typically come in do not resolve the seeing as well as bigger scopes. This can provide a steadier image leading to the false belief it's a more detailed image than a larger scope can provide. It can therefore appear more aesthetically pleasing. This factor coupled with number 1 are the two main things driving APO hype.

 

3. The maximized aperture potential, plus better aesthetics under seeing conditions ALSO couple with the following potent ingredient: Less apparent irradiation.  Meaning, 200x through a 4" is providing an image that's bright but not excessively so. There isn't the glare associated with say, 200x through an 8".  Some refractor folks love to tout this as a result of superior contrast and so on, but it's simply that the small apertures need to work at a higher power per inch of aperture negating the effects of excessive irradiation.   

 

In a nutshell, because the APOs are so very efficient it can lead to boastful claims against other larger less aperture effective designs.  The hard reality of it all though is that even with the seeing effects degrading the image, higher irradiation at lower power per inch and so on, the less aesthetically large aperture scope view will trounce the smaller apertures .   Contrast aside, no small aperture APP, despite maximized contrast efficiency can get past it's angular resolution limits. 

 

Me, I think APOs are great. At night's out at a site frequented by others where inevitably the APO makes an appearance it's always a pleasure, sometimes a revelation.  I never really see it in the light of challenging other scopes but a sampled view of what it's like to look through a virtually perfect aperture.

 

Pete


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#145 Arizona-Ken

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Posted 05 January 2018 - 12:36 PM

 

From Arizona Ken's signature:

 

"Considered as a collector of rare and precious things, the amateur astronomer has a great advantage over amateurs in other fields ... the amateur astronomer has access at all times to the original objects of his study; the masterworks of the heavens belong to him as much as to the great observatories of the world. And there is no privilege like that of being allowed to stand in the presence of the original."

--Robert Burnham Jr, Burnham's Celestial HandbookHandbook

 

Jon

 

Thanks Jon.

 

-------

 

Tonight looks like it might be good for a few hours and I'm gonna exercise that exact privilege we all have. Ain't gonna worry about the "crucial" equipment issues that we talk about here, as I know what equipment I have, their strengths and limitations and how to use them effectively. After all these years, the equipment no longer gets in the way of what I want to do. Hope the weather is good where everyone is, if not tonight, then soon. Get out there!  ubetcha.gif

 

Arizona Ken


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#146 treadmarks

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Posted 05 January 2018 - 02:06 PM

You are right Erik, of course I know that most people are forced to accept the quality that is commercially aviable.
In my 40 years of experience especially with SCT's, I only saw a very few that had exellent optics. They are a very very rare breed indeed, and even when you find one, you still need to do some extra (insulation) work to make them as stable as a high quality apochromatic refractor.

It seems we are at the mercy of Synta et al. We can either buy their scopes, get a home-made / custom job for $$$, or give up. But to be completely fair, I think some of the compromises Celestron etc. makes are not without merit. Cassegrains are hardly the only telescopes being compromised by cost concerns. If the C8 cost twice as much, would I still own one? Or would it have ceased production 30 years ago due to lack of interest? An F/15 SCT with a 23% CO can be made, but it'll be bigger, heavier, and an even narrower FOV.

 

I chose the Nexstar 8SE and Cassegrains generally knowing that I was sacrificing optical "excellence" in the name of having a smaller, more usable, affordable telescope with go-to that will maximize my observing sessions and the number of objects I can see in a night. So yeah, I don't think it is helpful to worry/obsess over optical quality. So far, I have not been disappointed by the views, quite the opposite, so I think I'll keep going.


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#147 bobhen

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Posted 05 January 2018 - 02:55 PM

Much can be done to improve the stability of the images in SCT and Mak telescopes under falling temperatures and I applaud those who try their best to find good solutions for this. 

The solution is a nice apo refractor! Sorry Eric just kidding but…

 

Here in Pennsylvania, even my open tube Mewlon 210 needs fans to facilitate cooling and eliminate heat plumes from reforming during the night if the temperature is falling, as it usually does on most nights during the year. The fans  I added to my Mewlon 210 do a nice job.

 

It really is criminal that Meade and Synta/Celestron (and yes even the Quester 7) don’t at least offer fans as an option for their SCT’s and Maks. Tak puts them in their upper-end Mewlons but even the 210 and 180 really need them.

 

Bob


Edited by bobhen, 05 January 2018 - 02:57 PM.

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#148 Mitrovarr

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Posted 05 January 2018 - 03:07 PM

I think the Edge scopes have cooling vents and it's easy to get third-party fans that work for them. It should be a stock feature, like it is in big dobs, though.

#149 bobhen

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Posted 05 January 2018 - 03:34 PM

I think the Edge scopes have cooling vents and it's easy to get third-party fans that work for them. It should be a stock feature, like it is in big dobs, though.

I realize that the Edge SCT’s have vents but fans or at least a port or two where fans could be added as an aftermarket accessory, should be on the back plate behind the mirror.

 

Meade did exactly that with their 7-inch Mak. So why not with SCT’s?

 

Bob



#150 Peter Besenbruch

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Posted 05 January 2018 - 03:53 PM

Well, one thing I've noticed is that SCT owners are often absolutely terrified of working on their scopes, but SCTs need collimation almost like a newtonian does. I see so many miscollimated SCTs - and the bigger they are, the more likely it is.

Yes, I spend a bit of time encouraging folks to "work the screws." My Maksutov is more tolerant of miscollimation, though I still don't like it. I put that down to the longer f-ratio primary that they typically use.




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