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1 inch APO vs 12 inch SCT

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#51 CHASLX200

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Posted 02 January 2018 - 07:11 AM

 

Yes, and a lot of the observers with big scopes who live in more favorable climates seemingly cannot possibly comprehend how it is to live in a challenging one. Quite a lot of my observing are unplanned, surprise half-hour to one-hour sessions between showers or low-pressure fronts. Under such conditions, the small refractor reigns supreme and allows me to get the best of the preciously few available photons. Some large-scope observers have even told me, that they would give up and find another hobby, if they were forced to live where I do. Yeah, but I didn't give up, I just found the best tool for the job and try to make the best of it.

I, too, live on an island surrounded by ocean, so our observing conditions must be the same. wink.gif

 

People have reviewed why a refractor might perform better than a Cat. Yes, inch for inch, a refractor is better. Yes, the refractors cool better, and aren't as affected by temperature changes. Yes, refractors lack a central obstruction. Yes, there are a lot of bad SCTs out there (though those times are supposed to be far in the past).

 

What constitutes "bad?" My 1982 vintage, orange C8 had maybe two nights total of reaching 250x on planets. No, it didn't do all that well when pushed higher. Is that bad? I give it a "meh minus." An 80mm Pentax refractor (your basic f11 achromat) produced nice, crisp, clean images of up to 200x most of the time. So did a defective Vixen 4" achromat. I have had Newtonians perform very well indeed. I have looked at planets through many other SCTs, but they never impressed.

 

Then there is my 7" Cat., a Maksutov that has spent a few nights over 500x. Good optics coupled with the usual cheap mechanics. Yet even at lover magnifications the images it produces pop, much like a refractor.

 

So what is it about SCTs? It's not the cooling (this is Hawaii, after all), and probably not the central obstruction (it's 5% more than my Maksutov). The conditions are good here, and they still lag as a group. Yes, there may be bad ones, but why are there so few that perform well out here. I suspect it's something about the design that makes great performances close to impossible. Either the design itself limits performance, much like a short focus achromat struggling to reach high magnifications, or it's a very fussy design that is hard to execute well.

 

I have owned around 60 SCT's and have some of the best seeing one could hope for in FL on the gulf coast. Most gave lack luster views at best. Four of them were very good and one black 1984 C8 was insane sharp and could do 450x+ on my best nites. As for the others like a Orange C14 i had they offered up mushy views of the planets compared to my well made Newts.  No cooling problems in my area as i never bother with high power work on nites with falling temps and most nites it can still be 86 at 10pm in the summer.

 

SCT's are just hit miss. One can be freaky good while another is a total mush dog.  I think the hit and miss was the worst with the orange C8's and Meades from the 80's.  But at the price you pay for a SCT ya just can't expect Zambuto like optics.


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#52 Arizona-Ken

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Posted 02 January 2018 - 08:14 AM

I am a DSO hunter and love my CPC1100. For a bit more portability my SE mounted '81 C8 gives great views. The narrow views are great; after all, I don't need a 3 degree view when I am hunting some 2 X 3 arc-minute galaxy.

 

In recent years I have used refractors for observing double stars and use an 80 mm, 127 mm and have a new 102 mm to use in the back yard. I have taken the 127 mm out to dark skies and the views are quite excellent.

 

The C8 and 127 are pretty close visually, but of the two, the 127 is a bit of a beast to use. The C8 brings out the dimmer stuff, the 127 mm gives great wider views.

 

The C8 and 102 mm are very close in portability, but the C8 is the better all around scope of the two. The 80 mm is grab and go for the moon and for white light solar work.

 

The best planetary views I have ever had have been with the CPC1100.

 

The lineup works well for me and in my experience scope use is a combination of three factors; cost, setup (portability, cool down, etc) and performance. In my lineup, SCTs are better per dollar, refractors are better per inch, and refractors are better to handle to about 4 inches when my SCTs take over. I'm sure an 8 or 9 inch refractor would give killer views compared to my CPC1100, but the scope and a suitable mount would would drain my bank account and require a crane or astro-roadies to take out to my dark sky sites.

 

For me, discussion of the benefits of each telescope type (including Newtonians) becomes meaningful when the three factors are discussed together. That there are strengths and weaknesses for each type of system and size of scope is why I have five of them.

 

Arizona Ken

 

 


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#53 PETER DREW

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Posted 02 January 2018 - 08:37 AM

The potential effect of internal tube currents on OTA's, spot the difference.

 

Refractor  -  1 converging pass.

 

Newtonian reflector - 1 parallel pass and 1 converging pass

 

Schmidt-Cassegrain - 1 parallel pass and 2 converging passes

 

Maksutov-Cassegrain - 1 diverging pass and 2 converging passes

 

The more passes the less chance of a textbook star image.


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#54 Daniel Mounsey

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Posted 02 January 2018 - 09:22 AM

Jon,

I think these discussions are interesting. The OP says... am I missing something? My answer to that is yes, you are missing something. The OP doesn't appear to understand the attributes of each optical system yet, probably because he hasn't had enough experience using each system on various types of targets to realize what they do differently which are arguable facts. If the OP understands this, then why is he asking this question in the first place, seeking answers? I then provided some examples of deep sky objects to help explain why a person would buy a frac or binos which has obviously fallen on some deaf ears because people are still running around like hamsters in a wheel, comparing the optical systems. It's like looking at a circle and a square and still debating whether or not they're different. Yes, they are different and here's why. Why do people make simple things so overly complicated? It's just common sense and instead, so many of these discussions drift off topic as debates about circles are squares and squares are circles. No, they're just different. I didn't discuss contrast effects on planets because that's another discussion in itself. smile.gif


Edited by Daniel Mounsey, 02 January 2018 - 09:24 AM.

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#55 treadmarks

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Posted 02 January 2018 - 10:01 AM

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.

Beyond that, I do think there's a lot of bad ones out there. I think bad reflectors get scrapped or refigured while bad SCTs circulate forever. They last better than newts and they cost more so nobody wants to be the one who finally 'retires' a lemon.

Agreed, and there is evidence to suggest manufacturing has gotten better. This is only natural as time goes on and technology improves. I got my SCT new in 2017 and I'd say it stays sharp up to at least 312X. In the long history of the C8 there were some famously bad periods where manufacturing standards dropped.

 

I see lots of old SCTs running around, the used market is very popular. The problem is you don't know what you're getting and unlike with new telescopes there is no return policy. Are people more likely to sell their good telescopes and keep their bad ones? And once you've been handed a bad one, are you going to want to eat the loss on it? No and no.


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#56 rmollise

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Posted 02 January 2018 - 10:33 AM

It’s actually a psychological issue.  When someone buys something that costs a lot of money, say a 5 inch APO for $7000, they then develop a “cognitive bias” where they need to justify to themselves that it was worth it.  Here’s an explanation from Wikipedia:

 

“In cognitive science, choice-supportive bias or post-purchase rationalization is the tendency to retroactively ascribe positive attributes to an option one has selected. It is a cognitive bias. For example, if a person chooses option A instead of option B, they are likely to ignore or downplay the faults of option A while amplifying those of option B. Conversely, they are also likely to notice and amplify the advantages of option A and not notice or de-emphasize those of option B.l

 

That is true to some extent, but it is also true that that 5-inch APO can do some things better than that 12-inch SCT.

 

The other syndrome is that people become emotionally attached to a brand or a design instead of looking upon a telescope for what it is, A TOOL.

 

Would you try to drive a nail with a screwdriver? I wouldn't. Not now, but I in effect tried to do that for more than a few years... ;)


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#57 rmollise

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Posted 02 January 2018 - 10:35 AM

 

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.

Beyond that, I do think there's a lot of bad ones out there. I think bad reflectors get scrapped or refigured while bad SCTs circulate forever. They last better than newts and they cost more so nobody wants to be the one who finally 'retires' a lemon.

Agreed, and there is evidence to suggest manufacturing has gotten better. This is only natural as time goes on and technology improves. I got my SCT new in 2017 and I'd say it stays sharp up to at least 312X. In the long history of the C8 there were some famously bad periods where manufacturing standards dropped.

 

I see lots of old SCTs running around, the used market is very popular. The problem is you don't know what you're getting and unlike with new telescopes there is no return policy. Are people more likely to sell their good telescopes and keep their bad ones? And once you've been handed a bad one, are you going to want to eat the loss on it? No and no.

 

A properly collimated SCT most assuredly doesn't need collimation like a Newtonian does. It should go months--if not years--before it needs re-tweaking. ;)


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#58 treadmarks

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Posted 02 January 2018 - 10:50 AM

The lineup works well for me and in my experience scope use is a combination of three factors; cost, setup (portability, cool down, etc) and performance. In my lineup, SCTs are better per dollar, refractors are better per inch, and refractors are better to handle to about 4 inches when my SCTs take over. I'm sure an 8 or 9 inch refractor would give killer views compared to my CPC1100, but the scope and a suitable mount would would drain my bank account and require a crane or astro-roadies to take out to my dark sky sites.

Actually, I would challenge the idea that refractors are better "per inch." What about cubic inches? ;) For me, the biggest selling point of a Cassegrain is that they pack the most performance per volume. Why is it meaningful to use only the aperture dimension when an 8" SCT is still more compact than a 4" refractor? My 8" SCT fits in my carry-on bag and my 4" "short" refractor does not. Cassegrains can come along on trips where suitcase or trunk space are limited.

 

There's no shortage of things to see, no matter what kind of telescope you have. So I think I'd rather measure performance by the number of things I see with my telescope over a night or over a year. Cassegrains are the most portable design, at least up to a C11. This can lead pretty straightforwardly to more usage. Add in the fact that Cassegrains work great with go-to, and I'd say I'm definitely getting more out of my Cassegrain than I would with any other telescope.


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#59 Astrojensen

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Posted 02 January 2018 - 10:57 AM

 

A properly collimated SCT most assuredly doesn't need collimation like a Newtonian does. It should go months--if not years--before it needs re-tweaking.

The same could actually be said about the newtonian. Why have we got used to newtonians that require recollimation all the time? In smaller apertures, it is EMINENTLY possible to construct a newtonian that holds collimation just as well as a maksutov or a refractor does. I know, because I have one. But then people would have to pay a bit extra and that's a big no-no with newtonians, so they prefer them to be sloppily built and need collimation all the time. They can get them cheaper than anything else, so they also WANT them cheaper than anything else, no matter what the design really is capable of. 

 

 

Clear skies!

Thomas, Denmark


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#60 Mitrovarr

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Posted 02 January 2018 - 11:17 AM


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.

Beyond that, I do think there's a lot of bad ones out there. I think bad reflectors get scrapped or refigured while bad SCTs circulate forever. They last better than newts and they cost more so nobody wants to be the one who finally 'retires' a lemon.

Agreed, and there is evidence to suggest manufacturing has gotten better. This is only natural as time goes on and technology improves. I got my SCT new in 2017 and I'd say it stays sharp up to at least 312X. In the long history of the C8 there were some famously bad periods where manufacturing standards dropped.

I see lots of old SCTs running around, the used market is very popular. The problem is you don't know what you're getting and unlike with new telescopes there is no return policy. Are people more likely to sell their good telescopes and keep their bad ones? And once you've been handed a bad one, are you going to want to eat the loss on it? No and no.
A properly collimated SCT most assuredly doesn't need collimation like a Newtonian does. It should go months--if not years--before it needs re-tweaking. ;)
I've had solid tube dobs that went months or years without needing recollimation.

Anyways, maybe they need it less often. But the fact remains that I see far more miscollimated SCTs than any other design. And some of them are really, really bad, like secondary shadow almost outside of the primary bad. People just don't seem to notice, or be aware that they need collimation. It's really stupid when you consider how easy a SCT is to collimate.

Edited by Mitrovarr, 02 January 2018 - 11:18 AM.

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#61 Astrojensen

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Posted 02 January 2018 - 11:26 AM

 

And some of them are really, really bad, like secondary shadow almost outside of the primary bad.

Been there, seen that. I told the owner, but he just shrugged and said it wasn't important for the kind of work he used the scope for... 

 

 

Clear skies!
Thomas, Denmark



#62 rmollise

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Posted 02 January 2018 - 12:10 PM

The same could actually be said about the newtonian. Why have we got used to newtonians that require recollimation all the time? In smaller apertures, it is EMINENTLY possible to construct a newtonian that holds collimation just as well as a maksutov or a refractor does. I know, because I have one. But then people would have to pay a bit extra and that's a big no-no with newtonians, so they prefer them to be sloppily built and need collimation all the time. They can get them cheaper than anything else, so they also WANT them cheaper than anything else, no matter what the design really is capable of. 
 
 
Clear skies!
Thomas, Denmark


The reason is that a lot of the Newtonians in use today are Dobsonians. Mirror cells vary, but a truss scope will for sure have to be collimated every single time. There's also the fact that you have an additional collimatable element.

That said, my solid tube Newt holds collimation pretty well. smile.gif



#63 Arizona-Ken

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Posted 02 January 2018 - 12:21 PM

 

The lineup works well for me and in my experience scope use is a combination of three factors; cost, setup (portability, cool down, etc) and performance. In my lineup, SCTs are better per dollar, refractors are better per inch, and refractors are better to handle to about 4 inches when my SCTs take over. I'm sure an 8 or 9 inch refractor would give killer views compared to my CPC1100, but the scope and a suitable mount would would drain my bank account and require a crane or astro-roadies to take out to my dark sky sites.

Actually, I would challenge the idea that refractors are better "per inch." What about cubic inches? wink.gif For me, the biggest selling point of a Cassegrain is that they pack the most performance per volume. Why is it meaningful to use only the aperture dimension when an 8" SCT is still more compact than a 4" refractor? My 8" SCT fits in my carry-on bag and my 4" "short" refractor does not. Cassegrains can come along on trips where suitcase or trunk space are limited.

 

There's no shortage of things to see, no matter what kind of telescope you have. So I think I'd rather measure performance by the number of things I see with my telescope over a night or over a year. Cassegrains are the most portable design, at least up to a C11. This can lead pretty straightforwardly to more usage. Add in the fact that Cassegrains work great with go-to, and I'd say I'm definitely getting more out of my Cassegrain than I would with any other telescope.

 

For most people, the "per inch" is a reference to light gathering power. Your "volumetric" inch is of course more of a reference to compactness and portability which I covered in my post in a different way. You say "potato" and I say "potahto."

 

Arizona Ken



#64 Scott Beith

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Posted 02 January 2018 - 12:33 PM

It’s actually a psychological issue.  When someone buys something that costs a lot of money, say a 5 inch APO for $7000, they then develop a “cognitive bias” where they need to justify to themselves that it was worth it.  Here’s an explanation from Wikipedia:

 

“In cognitive science, choice-supportive bias or post-purchase rationalization is the tendency to retroactively ascribe positive attributes to an option one has selected. It is a cognitive bias. For example, if a person chooses option A instead of option B, they are likely to ignore or downplay the faults of option A while amplifying those of option B. Conversely, they are also likely to notice and amplify the advantages of option A and not notice or de-emphasize those of option B.l

I respectfully disagree with you on this one.  Since my 5" apo was acquired for $0.00 dollars due to the generosity of the wonderful folks at Astronomics, I don't have to justify the performance based on $$$ layed out on the purchase.  Scopes do what scopes do - meaning that the characteristics and attributes of each individual design (and implementation of that design) when combined with seeing conditions determine the performance of that particular set of optics at that particular time.  I tend to believe that people drawn to high end apochromatic scopes are a rather picky bunch of folks.  If you watch the discussions on CN's they debate endlessly on .997 strehl vs. .998 strehl, color correction at 100X/inch of aperture, and contrast levels capable of discerning minute low contrast details on planets.

 

That being said - if they are picky about (and truthful about) minute differences between refractive optics, I tend to believe they can tell the performance differences between mirrored scopes and refractors.  If you are looking for the highest quality optics available, you tend to be picky about the views presented in the EP - no matter what the design.

 

I think the majority of the folks here on CN's who choose high end optics, whether they prefer big achromats (like D&G), tiny apochromats, or  a Takahashi Mewlon have a full realization of the performance benefits and limitations of these scopes.  

 

Setting scopes side by side on a particular evening usually gives "the expected" results related to resolution and sharpness, but depending on the conditions, you might find the results don't always match theory...   ;)


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#65 Mitrovarr

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Posted 02 January 2018 - 12:43 PM

 

It’s actually a psychological issue.  When someone buys something that costs a lot of money, say a 5 inch APO for $7000, they then develop a “cognitive bias” where they need to justify to themselves that it was worth it.  Here’s an explanation from Wikipedia:

 

“In cognitive science, choice-supportive bias or post-purchase rationalization is the tendency to retroactively ascribe positive attributes to an option one has selected. It is a cognitive bias. For example, if a person chooses option A instead of option B, they are likely to ignore or downplay the faults of option A while amplifying those of option B. Conversely, they are also likely to notice and amplify the advantages of option A and not notice or de-emphasize those of option B.l

I respectfully disagree with you on this one.  Since my 5" apo was acquired for $0.00 dollars due to the generosity of the wonderful folks at Astronomics, I don't have to justify the performance based on $$$ layed out on the purchase.  Scopes do what scopes do - meaning that the characteristics and attributes of each individual design (and implementation of that design) when combined with seeing conditions determine the performance of that particular set of optics at that particular time.  I tend to believe that people drawn to high end apochromatic scopes are a rather picky bunch of folks.  If you watch the discussions on CN's they debate endlessly on .997 strehl vs. .998 strehl, color correction at 100X/inch of aperture, and contrast levels capable of discerning minute low contrast details on planets.

 

That being said - if they are picky about (and truthful about) minute differences between refractive optics, I tend to believe they can tell the performance differences between mirrored scopes and refractors.  If you are looking for the highest quality optics available, you tend to be picky about the views presented in the EP - no matter what the design.

 

I think the majority of the folks here on CN's who choose high end optics, whether they prefer big achromats (like D&G), tiny apochromats, or  a Takahashi Mewlon have a full realization of the performance benefits and limitations of these scopes.  

 

Setting scopes side by side on a particular evening usually gives "the expected" results related to resolution and sharpness, but depending on the conditions, you might find the results don't always match theory...   wink.gif

 

I dunno. You still know what the scope should cost, so the effect should still be in play. You don't have to pay for it, you just have to know that it's valuable.

 

Also, one might wonder if the reason that setting scopes side by side often gives the expected result is because that result was expected by the observers. I mean, at least some of the time - some of the result is undoubtedly real, but some could be psychological. It is very difficult to separate out the two without some form of objective testing.

 

It's really a pity that good, blind testing is nearly impossible for astronomy equipment, because it is almost impossible to disguise most of it from the viewer and experienced observers are needed



#66 Scott Beith

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Posted 02 January 2018 - 12:48 PM

 

One object people don't realize they can see in stunning clarity from a dark sky is the North American Nebula. It amazes me how much propaganda and emphasis with detailed maps are given to the Horse Head Nebula, which is far more difficult to see than the North American, yet you can see the North America the best in stunning contrast with an 80mm or 100mm frac using a UHC filter. It doesn't look as good in my larger fracs. Try to see this in your SCT.

 

 

Daniel:

 

So much publicity is given to things like the Horsehead and the central star in M57..  These are difficult targets that are Class II amazing: "amazing that you can see them at all."  There's so much hoopla about the central star in M57, one might have the impression that when one finally sees it, it suddenly becomes brighter than Sirius. whee.gif  The reality, it's still just a faint star that's difficult to see because it's embedded in a Nebula.  I will admit to spending a lot of time on Horsehead, its one of those "the more you look, the more you see" objects.   

 

The North American, the Veil, these are Class I amazing.  that is, they're just amazing to look at.  The North American/Pelican complex is probably not much in an SCT but it's pretty awesome in a big dob with UHC filter, a large exit pupil and wide field of view.  The Veil, it's another one that is amazing is both smaller scopes with wider fields and large aperture scopes.  Its good my NP-101 with a 31mm Nagler or 41mm Panoptic with an O-III or the 16 inch or 22 inch.. Anything really.

 

I have had some amazing wide field views of the Veil with a 24mm TV WF fitter with a O-III filter in my 50mm SV finder.  

 

I was like most of you until I tried the cool aid.  now I can drink enough.

 

 

I have the "cool aid".  It's nice.  But it's just part of the picture.  If your C-11 didn't provide clean splits of near Dawes limit doubles I suspect it probably never reached thermal equilibrium on a night when the seeing was excellent.  Or maybe you just needed a Newtonian and the patience to make it strut its stuff.  smile.gif

 

Jon

 

Jon I like the Class I and Class II amazing categories Sir.  bow.gif


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Posted 02 January 2018 - 01:58 PM

For most people, the "per inch" is a reference to light gathering power. Your "volumetric" inch is of course more of a reference to compactness and portability which I covered in my post in a different way. You say "potato" and I say "potahto."
 
Arizona Ken

I'll admit I was equivocating, but my point was that "per aperture" measures are more of theoretical importance than practical importance. And I think it's actually deceptive, because it implies that size for size a refractor will perform better than a Cassegrain. That's only true if you're thinking in one dimension.



#68 mikona

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Posted 02 January 2018 - 02:30 PM

Hello Friends,

 

For what it is worth, I would like to clarify a bit.  I loved my CPC1100.  So much so, that I recommended one to my friend, who just bought one used here on cloudy nights.  He is most interested in Galaxies and faint DSO's.  And, for what it is worth, once we collimated his scope, it performed very well.  The views were very solid.  It took time for his system to cool, but I don't think it ever quite hit equilibrium.  Now, I set up my ES127ED right next to his scope that night.  Here was the conclusion from both of us... The CPC provided significantly brighter images and provided more detail for sure.  However, the clarity and contrast of the images and quality of the stars was noticeably better in the 5 inch refractor.  In fact, we both preferred the image of Orion in the 5 inch to the CPC1100.  Now, if equilibrium had been achieved, that might have changed things... but after 2 plus hours of viewing, the final results were what they were.

 

I have a Mewlon 250 for high performance deep sky and planetary/lunar viewing.  After letting the Mewlon cool for 2.5 hours (used my 4 inch Takahashi in the meantime), the Mewlon put up splendid images of Orion and every other target I viewed.  GREAT contrast... Almost 3D.  However, even with the Mewlon cooled, the 4 inch Tak had better looking, pinpoint stars.

 

A bit over a month ago, I had the privilege of looking through a new 20" Teeter f3.3 with a SIPS system.  The image I saw of the Swan was breathtaking.  I was literally speechless.  It was almost a spiritual experience.  Really, the Swan looked almost photographic.  Stars were clean to the edge.  However, the stars, as clean as they were, were not nearly as pinpoint and precise as my fracts.  They too were a bit bloated.

 

So, I have yet to look through another optical system that makes images so incredibly contrasty and precise.  Even when more data is available to the eye, it isn't as crisp as the refractors I have looked through.  That isn't to say that the other optical systems aren't great... they are, but they come with sacrifices... as does the refractor - usually with limited aperture.

 

I do live in Los Angeles, so if any of you have another system that you would like me to look through that is comparable to the contrast and clarity of a refractor... please hit me up.  I would love to view through your instrument, meet new friends, and learn something new.

 

I have multiple Refractors a Dall Kirkham Cassegrain, and a Reflector.  Each has its purpose and I enjoy them all.  But, for purity of image, the fracts take the cake.  When out galaxy hunting, I will chose another weapon of choice!


Edited by mikona, 02 January 2018 - 02:32 PM.


#69 sg6

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Posted 02 January 2018 - 03:03 PM

I susect that part of it is the operation of the eye. All the talk tends to be of how big and how much light a scope gathers but the eye operates on both brightness and contrast.

 

Where something starts is easier to define if the edge and so the contrast change is better defined and that is where a refractor tends to win out, especially the ED and apo's. People talk of a refractor snapping into focus, it is not commoin in the 2 other general designs. That better contrast makes it appear brighter.

 

So in a way a slightly smaller good refractor compares to a bit bigger reflector/SCT type but the comparison is on the contrast or edge change, and more relevant it is the eye and operation of the brain. In electronics a rising or falling edge is often used to trigger an event and the design is to get a good riing or falling edge not a long slow ramp up or down.

 

It is kind of similar to the moon and M42. Just about eveyone looking up would say the moon is by far the bigger, but it is not.

 

In a way it is odd that the eye is ignored or forgotten about, but it tends to be important, or at least very relevant.



#70 turtle86

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Posted 02 January 2018 - 03:20 PM

Jon,

I think these discussions are interesting. The OP says... am I missing something? My answer to that is yes, you are missing something. The OP doesn't appear to understand the attributes of each optical system yet, probably because he hasn't had enough experience using each system on various types of targets to realize what they do differently which are arguable facts. If the OP understands this, then why is he asking this question in the first place, seeking answers? I then provided some examples of deep sky objects to help explain why a person would buy a frac or binos which has obviously fallen on some deaf ears because people are still running around like hamsters in a wheel, comparing the optical systems. It's like looking at a circle and a square and still debating whether or not they're different. Yes, they are different and here's why. Why do people make simple things so overly complicated? It's just common sense and instead, so many of these discussions drift off topic as debates about circles are squares and squares are circles. No, they're just different. I didn't discuss contrast effects on planets because that's another discussion in itself. smile.gif

I agree. Refractors, reflectors, and SCT's represent optical compromises to some extent and have their different strengths and weaknesses.  The observer needs to figure what he wants to observe, how he wants to observe it, and then pick the right tool for the right job.


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#71 junomike

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Posted 02 January 2018 - 04:04 PM

It’s actually a psychological issue.  When someone buys something that costs a lot of money, say a 5 inch APO for $7000, they then develop a “cognitive bias” where they need to justify to themselves that it was worth it.  Here’s an explanation from Wikipedia:

 

“In cognitive science, choice-supportive bias or post-purchase rationalization is the tendency to retroactively ascribe positive attributes to an option one has selected. It is a cognitive bias. For example, if a person chooses option A instead of option B, they are likely to ignore or downplay the faults of option A while amplifying those of option B. Conversely, they are also likely to notice and amplify the advantages of option A and not notice or de-emphasize those of option B.l

I'm not disagreeing however there's an equal and opposite condition known as "Unobtanium Rationaliztion" were one tends to make excuses/justify for not wanting something that costs more money than they either can afford or want to afford, thus convincing themselves that their current gear is just good.......or close enough.

 

Either condition still results in positive enjoyment of the hobby thus Dr's have rendered both conditions harmless.


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#72 Migwan

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Posted 02 January 2018 - 05:14 PM

 

It’s actually a psychological issue.  When someone buys something that costs a lot of money, say a 5 inch APO for $7000, they then develop a “cognitive bias” where they need to justify to themselves that it was worth it.  Here’s an explanation from Wikipedia:

 

“In cognitive science, choice-supportive bias or post-purchase rationalization is the tendency to retroactively ascribe positive attributes to an option one has selected. It is a cognitive bias. For example, if a person chooses option A instead of option B, they are likely to ignore or downplay the faults of option A while amplifying those of option B. Conversely, they are also likely to notice and amplify the advantages of option A and not notice or de-emphasize those of option B.l

I'm not disagreeing however there's an equal and opposite condition known as "Unobtanium Rationaliztion" were one tends to make excuses/justify for not wanting something that costs more money than they either can afford or want to afford, thus convincing themselves that their current gear is just good.......or close enough.

 

Either condition still results in positive enjoyment of the hobby thus Dr's have rendered both conditions harmless.

 

And then there good old conceit.  The idea that millions of SCT owners are just plain wrong with their mushy views, seems a little vein.   So to, is the view that all those millions with skinny fracs  are dumb cause they are coming up short on galaxies. 

 

From where I'm at, the stars look great and the galaxies close by.  If anyone ever catches me dissing someone for the type of scope they own, please kick me promptly in my posterior tuberosity.

Thankyou.

 

jd


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#73 WadeH237

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Posted 02 January 2018 - 05:51 PM

I'll admit I was equivocating, but my point was that "per aperture" measures are more of theoretical importance than practical importance. And I think it's actually deceptive, because it implies that size for size a refractor will perform better than a Cassegrain. That's only true if you're thinking in one dimension.

This.

 

Performance per inch of aperture is pretty useless outside of design discussions.  In the real world, the scalability of a design matters.  It would be nice to compare an 8" SCT to an 8" refractor, but then you realize that a quality 8" APO refractor requires a huge mount and costs more than the average new car.


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#74 yellobeard

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Posted 02 January 2018 - 06:20 PM

Refractor/reflector discussions.. They always end up not providing a solid answer! What one writes, is disputed by someone else.

 

Refractors are totally different from reflectors, and one loves refractors, the other loves reflectors.

One of the biggest problems with commercial telescopes is in the factory tolerances.

 

A C8 is very well capable of giving a perfect 6" APO refractor a run for its money, theoretically! So why doesn't it do just that? Well, if the C8's optics would have been manufactured with no compromises, then the situation would be way different.

Many immediately point at the central obstruction as the main cause for the not so great image in an average C8, which also can be disputed.

Furthermore, the optical path in a refractor is much simpeler than in a SCT, and is therefor less affected by tube currents.

If the optical quality of the surfaces on the seperate optical elements would be the same, the SCT would give a poorrer image, why? Because reflective optics in the SCT are more suseptible to surface errors.

 

SCT's do not produce 'soft images' .. Most commercial SCT's sadly do!

 

After I modified some commercial SCT's, taking away their flaws, a world of great stargazing moments opened up to me! And now, with my new 16" SCT, build with no compromises, I'm totally in love with the SCT system.

 

Mostly because they have smaller apertures than the average reflectors, refractors are great for wide field observing and photography, so they have their place.

Those who have the money can buy the bigger APO refractors, build with very narrow tolerances, but they should not compare them with a with a cheaper SCT that was build with bigger tolerances in mind.

 

Yes, I'm a spoiled guy, because I can make my own perfect scope.. Most of you are destined to accept the factory tolerances that make the refractor/reflector discussion a lot less fair towards the telescope types themselves, but I understand that the factory tolerances force me to accept that the SCT as an optical system still does not get the positive kudo's it deserves.. I must accept it because it is the reality of today

Of course, the same goes for any other well known reflector telescope type.


Edited by yellobeard, 02 January 2018 - 06:23 PM.

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#75 CHASLX200

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Posted 02 January 2018 - 06:45 PM

Refractor/reflector discussions.. They always end up not providing a solid answer! What one writes, is disputed by someone else.

 

Refractors are totally different from reflectors, and one loves refractors, the other loves reflectors.

One of the biggest problems with commercial telescopes is in the factory tolerances.

 

A C8 is very well capable of giving a perfect 6" APO refractor a run for its money, theoretically! So why doesn't it do just that? Well, if the C8's optics would have been manufactured with no compromises, then the situation would be way different.

Many immediately point at the central obstruction as the main cause for the not so great image in an average C8, which also can be disputed.

Furthermore, the optical path in a refractor is much simpeler than in a SCT, and is therefor less affected by tube currents.

If the optical quality of the surfaces on the seperate optical elements would be the same, the SCT would give a poorrer image, why? Because reflective optics in the SCT are more suseptible to surface errors.

 

SCT's do not produce 'soft images' .. Most commercial SCT's sadly do!

 

After I modified some commercial SCT's, taking away their flaws, a world of great stargazing moments opened up to me! And now, with my new 16" SCT, build with no compromises, I'm totally in love with the SCT system.

 

Mostly because they have smaller apertures than the average reflectors, refractors are great for wide field observing and photography, so they have their place.

Those who have the money can buy the bigger APO refractors, build with very narrow tolerances, but they should not compare them with a with a cheaper SCT that was build with bigger tolerances in mind.

 

Yes, I'm a spoiled guy, because I can make my own perfect scope.. Most of you are destined to accept the factory tolerances that make the refractor/reflector discussion a lot less fair towards the telescope types themselves, but I understand that the factory tolerances force me to accept that the SCT as an optical system still does not get the positive kudo's it deserves.. I must accept it because it is the reality of today

Of course, the same goes for any other well known reflector telescope type.

I would like to see Zambuto or Mike Lockwood work on one of these run of the mill SCT's.  I am sure it would cost much more.




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