215 replies to this topic

[jrbarnett]

 

 

I wonder if the graph is supposed to take into account the usual atmospheric disturbances that often limit seeing and usable resolution?

That is often said to make a 6" scope optimum on the idea 6" x 50x per inch =300x ,the "typical" maximum due to conditions.

 

The reality is that if the conditions are such that a 6 inch scope shows all it can show,  a decent 12 inch scope will show more. 

 

Jon

 

Not always.  We had two 12" scopes in the Mojave that couldn't show Sirius B when both a 5.5" and 3" scope could do it.

 

- Jim

[Daniel Mounsey]

 

Well it's a digression but I've never understood the fascination for splittng stars in small (say five or six inch) refractors.  When you push the magnification the stars become dots.  I don't like looking at Airy disk dots.  

 

Too funny.  That's what I strive for as I can't stand it when stars are not those pretty little dots -- perfectly formed, sharp edges, nice and round, no wool!

 

 Hey wait a minute Bill, I thought you liked those wooly stars!

[gezak22]

While I have gone over to the 'dark side' (imaging) a couple of years ago, I recently acquired a pair of 10x70 Fujinons, so I can do some observing. Is it serious observing? Maybe, maybe not, I don't really care - I am having a good time with them and that's all that matters to me.

[russell23]

The ED doublets and triplets are great.  But the idea that an APO can completely compensate for the light not focused in the Airy disc of a larger aperture achromat has its limits.  When I compared an 80mm Vixen ED doublet against my Vixen 140NA with the Baader 495 Longpass filter it was no contest on deep sky and lunar observations. The larger aperture showed a lot more details and resolution.  If the unfocused light and light removed with the Longpass filter was a combined 30% (it is certainly less than that by quite a bit) then I would need a 117mm APO to match the Vixen 140 refractor.  

 

So I wouldn't go trading in a 5.5-6 inch achromat for a 110mm or smaller APO.   At brand new prices I might take a 120mm ED doublet over the Vixen 140.  But anything smaller than the 120 ED would be a poor choice as a substitute for a 140-150mm achromat with good optical figure - unless you don't mind losing light and details.  

 

Dave

[schang]

 

Well it's a digression but I've never understood the fascination for splittng stars in small (say five or six inch) refractors.  When you push the magnification the stars become dots.  I don't like looking at Airy disk dots.  

 

Too funny.  That's what I strive for as I can't stand it when stars are not those pretty little dots -- perfectly formed, sharp edges, nice and round, no wool!

 

There is a way to make the wooly stars shedding their wools in a Dob... by using an aperture mask.  One can not make a scope larger, but for a large Dob, it is a piece of cake to make it smaller, from 4" all the way to 6" in a 15" Dob.  I have a 3.75" aperture mask on my 10" Dob, which I sometimes use it for double star viewing.

Edited by schang, 09 August 2014 - 10:03 PM.

[Jon Isaacs]

 

 

Well it's a digression but I've never understood the fascination for splittng stars in small (say five or six inch) refractors.  When you push the magnification the stars become dots.  I don't like looking at Airy disk dots.  

 

Too funny.  That's what I strive for as I can't stand it when stars are not those pretty little dots -- perfectly formed, sharp edges, nice and round, no wool!

 

There is a way to make the wooly stars shedding their wools in a Dob... by using an aperture mask.  One can not make a scope larger, but for a large Dob, it is a piece of cake to make it smaller, from 4" all the way to 6" in a 15" Dob.  I have a 3.75" aperture mask on my 10" Dob, which I sometimes use it for double star viewing.

 

 

Spitting doubles at at high magnifications, in my various Newtonians, I don't see the diffraction spikes from the spiders with the vast majority of doubles.  The stars are round and tight... 

 

YMMV

 

Jon

[Sarkikos]

 

 

 

Well it's a digression but I've never understood the fascination for splittng stars in small (say five or six inch) refractors.  When you push the magnification the stars become dots.  I don't like looking at Airy disk dots.  

 

Too funny.  That's what I strive for as I can't stand it when stars are not those pretty little dots -- perfectly formed, sharp edges, nice and round, no wool!

 

There is a way to make the wooly stars shedding their wools in a Dob... by using an aperture mask.  One can not make a scope larger, but for a large Dob, it is a piece of cake to make it smaller, from 4" all the way to 6" in a 15" Dob.  I have a 3.75" aperture mask on my 10" Dob, which I sometimes use it for double star viewing.

 

 

Spitting doubles at at high magnifications, in my various Newtonians, I don't see the diffraction spikes from the spiders with the vast majority of doubles.  The stars are round and tight... 

 

YMMV

 

Jon

 

My mileage is right there with yours. I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else - or you don't want to bother with the weight and bulk of the larger scope. 

 

Mike

Edited by Sarkikos, 10 August 2014 - 01:49 PM.

[Daniel Mounsey]

That's ironic considering the array of small scopes on your scope list. Am I missing something or is this the jamie kennedy experiment?

[Sarkikos]

The smaller scopes in my sig show that I have the experience to know what I'm talking about!

 

But don't assume that I only look at double stars. Or that I only use the biggest aperture I have.  Maybe you missed the end of my post. It says that sometimes I "don't want to bother with the weight and bulk of the larger scope."  The real advantage of smaller scopes is the lighter weight, quicker acclimation, and less encumbered grab-n-go.  

 

Some of those scopes will be on sale soon, but only because I recently bought a C80ED. The small achros don't cut it for me anymore ... not that they ever really did.

 

Jamie Kennedy Expeiment? I don't follow those creeds.

 

Mike

Edited by Sarkikos, 11 August 2014 - 06:30 AM.

[BillP]

I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ...

 

 

Interesting.  Of the zillion or so doubles up there that a small scope can spilt, what makes the other zillion or so doubles that only a larger scope can split any different or better?  Do those tighter doubles that need a larger scope do some sort of special dance once you split them that the smaller scope doubles don't?  Or do they start changing colors when you spilt them?  Since doubles for any aperture scope offer the same level of *challenge* relative to their respective scopes, those tighter doubles must do some pretty spectacular things once you split them that the less close doubles don't do.    Guess I've been missing it all these years and now need to haul out my 10" scope to split doubles instead of the 4" that I much much prefer. 

 

For me the advantage of the smaller scope is that I can get those pretty little airy disks with less magnification, and that I can do this with much less effort since the smaller scope is so much lighter and can do it much more quickly as the smaller scope has no thermal acclimation or setup time.  And even with the smaller scope there are more than a lifetime of doubles to find, and there is just as much challenge.  Actually, there may be more challenge as with the smaller scope the challenege revolves more around pushing the optic to its limit whereas with the larger scope the challenge is more waiting for a steady enough night when one can actually push the optic.

Edited by BillP, 11 August 2014 - 08:39 AM.

[Sarkikos]

 

I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ...

 

 

Interesting.  Of the zillion or so doubles up there that a small scope can spilt, what makes the other zillion or so doubles that only a larger scope can split any different or better?  Do those tighter doubles that need a larger scope do some sort of special dance once you split them that the smaller scope doubles don't?  Or do they start changing colors when you spilt them?  Since doubles for any aperture scope offer the same level of *challenge* relative to their respective scopes, those tighter doubles must do some pretty spectacular things once you split them that the less close doubles don't do.    Guess I've been missing it all these years and now need to haul out my 10" scope to split doubles instead of the 4" that I much much prefer. 

 

For me the advantage of the smaller scope is that I can get those pretty little airy disks with less magnification, and that I can do this with much less effort since the smaller scope is so much lighter and can do it much more quickly as the smaller scope has no thermal acclimation or setup time.  And even with the smaller scope there are more than a lifetime of doubles to find, and there is just as much challenge.  Actually, there may be more challenge as with the smaller scope the challenege revolves more around pushing the optic to its limit whereas with the larger scope the challenge is more waiting for a steady enough night when one can actually push the optic.

 

 

I think maybe you and Daniel's reading comprehension skills are beginning to falter in your advancing years. :   

 

Neither of you acknowledged the last clause of my sentence: "I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ... or you don't want to bother with the weight and bulk of the larger scope." Many nights my 10" Dob sits in the house while I choose a smaller scope to take out for an observing session. That's not because the smaller scope performs better, but because it's, well ... smaller.

 

 
Mike

Edited by Sarkikos, 11 August 2014 - 08:53 AM.

[Jon_Doh]

It may just be that I don't know enough of anything, but I find plenty of beautiful, colorful doubles to split in my 120 APO refractor.

[Daniel Mounsey]

 

I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ...

 

 

Interesting.  Of the zillion or so doubles up there that a small scope can spilt, what makes the other zillion or so doubles that only a larger scope can split any different or better?  Do those tighter doubles that need a larger scope do some sort of special dance once you split them that the smaller scope doubles don't?  Or do they start changing colors when you spilt them?  Since doubles for any aperture scope offer the same level of *challenge* relative to their respective scopes, those tighter doubles must do some pretty spectacular things once you split them that the less close doubles don't do.    Guess I've been missing it all these years and now need to haul out my 10" scope to split doubles instead of the 4" that I much much prefer. 

 

For me the advantage of the smaller scope is that I can get those pretty little airy disks with less magnification, and that I can do this with much less effort since the smaller scope is so much lighter and can do it much more quickly as the smaller scope has no thermal acclimation or setup time.  And even with the smaller scope there are more than a lifetime of doubles to find, and there is just as much challenge.  Actually, there may be more challenge as with the smaller scope the challenege revolves more around pushing the optic to its limit whereas with the larger scope the challenge is more waiting for a steady enough night when one can actually push the optic.

 

 

Well stated Bill and precisely my point. The most baffling thing to me though is why some others who apparently have experience still don't realize this. I'm still trying to wrap my head around that. I have the option to roll out a few different high quality scopes at any given moment, a 4" apo, 6" apo and a 10" DK etc. I have no reason to roll out any 6" or 10" etc for doubles unless the target requires more aperture to be resolved even if the seeing is excellent. I still often use the 4" apo because countless doubles in my Burnham's Celestial Hanbook can be resolved beautifully in a 4" and so there's no need to use anything larger. Why don't others see that this is all relative. For example I was observing Achird the other night. In order to enjoy the view, do I need to bring out the most extreme large aperture I've got? I just don't get some of the posts in these forums sometimes regarding this constant beating about observers gotta have the largest telescope for everything they look at. 

[BillP]

Neither of you acknowledged the last clause of my sentence: "I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ... or you don't want to bother with the weight and bulk of the larger scope."

 

 
Mike

 

 

Well I don't know.  Thought I acknowleged it quite well when I pointed out that the smaller scope has advantage in that you can attain the pretty airy disk at lower magnifications...that you can actually challenge the optic more instead of the seeing...and that the thermal issues are just never there like with the larger scope.  So those three points have nothing to do with the weight and bulk.  Hmmm...whose getting old       (all in fun).

 

The way I see it is that I just don't see the advantage to larger aperture for double stars unless perhaps the seeing is very good - in which case you really should be viewing something else! 

[Sarkikos]

 

 

I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ...

 

 

Interesting.  Of the zillion or so doubles up there that a small scope can spilt, what makes the other zillion or so doubles that only a larger scope can split any different or better?  Do those tighter doubles that need a larger scope do some sort of special dance once you split them that the smaller scope doubles don't?  Or do they start changing colors when you spilt them?  Since doubles for any aperture scope offer the same level of *challenge* relative to their respective scopes, those tighter doubles must do some pretty spectacular things once you split them that the less close doubles don't do.    Guess I've been missing it all these years and now need to haul out my 10" scope to split doubles instead of the 4" that I much much prefer. 

 

For me the advantage of the smaller scope is that I can get those pretty little airy disks with less magnification, and that I can do this with much less effort since the smaller scope is so much lighter and can do it much more quickly as the smaller scope has no thermal acclimation or setup time.  And even with the smaller scope there are more than a lifetime of doubles to find, and there is just as much challenge.  Actually, there may be more challenge as with the smaller scope the challenege revolves more around pushing the optic to its limit whereas with the larger scope the challenge is more waiting for a steady enough night when one can actually push the optic.

 

 

Well stated Bill and precisely my point. The most baffling thing to me though is why some others who apparently have experience still don't realize this. I'm still trying to wrap my head around that. I have the option to roll out a few different high quality scopes at any given moment, a 4" apo, 6" apo and a 10" DK etc. I have no reason to roll out any 6" or 10" etc for doubles unless the target requires more aperture to be resolved even if the seeing is excellent. I still often use the 4" apo because countless doubles in my Burnham's Celestial Hanbook can be resolved beautifully in a 4" and so there's no need to use anything larger. Why don't others see that this is all relative. For example I was observing Achird the other night. In order to enjoy the view, do I need to bring out the most extreme large aperture I've got? I just don't get some of the posts in these forums sometimes regarding this constant beating about observers gotta have the largest telescope for everything they look at. 

 

Well, actually not so well stated since Bill snipped out the last clause of my sentence and you disregarded it. What's baffling to me is how two otherwise intelligent people can have such poor reading comprehension. Again here is my full sentence, unedited:

 

"I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ... or you don't want to bother with the weight and bulk of the larger scope."

 

I have no horse in this rodeo. It doesn't matter to me how anyone else goes about this hobby. After all, it is just a hobby. I'm only stating my opinion based on my experience. But I tell you, if I had an observatory, in a dark glare-free location, with a nice moderately large telescope - say, 14" or so - permanently mounted, with excellent optics, thermal stabilization, goto and tracking, do you think I'd spend as much time with the little grab-n-go scopes as I do now?  I doubt it.  Of course, there's a lot of "if"'s in that scenario, and it will probably never come to pass.  So I'll continue to have many enjoyable observing sessions with the little grab-n-go's.

 

Mike

Edited by Sarkikos, 11 August 2014 - 09:35 AM.

[PowellAstro]

@ BillP

 

+1

 

 

@ Sarkikos

 

I do have a 14 in a fixed Dome and I find myself most of the time using a smaller scope to view the night sky.  The 14 I have is very sharp, better than 1/10 wavefront but only on very rare nights does it provide the wow factor. On those rare nights of steady seeing nothing will touch it but on all the other nights I find the views through one of the smaller scopes more pleasing.  This is because I do a lot of viewing of the planets and double stars.  Most nights by the time I get to around 130x, the 14 shows rolling stars due to the seeing and not the scope.  On these same nights I can use the 102 refractor at 300x and see the airy disk.  Yes, it moves and jumps but there is just one airy disk. The 14 at this same power shows hundreds of airy disks and their movement is so fast I have one big fuzzy ball, which I don't like.  I have had rare nights that I have viewed doubles in the 14 at 1000x and the airy disk were text book and the detail on Saturn at 700x was unbelievable but those nights are so few.

Edited by PowellAstro, 11 August 2014 - 09:52 AM.

[Jon Isaacs]

 

Well stated Bill and precisely my point. The most baffling thing to me though is why some others who apparently have experience still don't realize this. I'm still trying to wrap my head around that. I have the option to roll out a few different high quality scopes at any given moment, a 4" apo, 6" apo and a 10" DK etc. I have no reason to roll out any 6" or 10" etc for doubles unless the target requires more aperture to be resolved even if the seeing is excellent. I still often use the 4" apo because countless doubles in my Burnham's Celestial Hanbook can be resolved beautifully in a 4" and so there's no need to use anything larger. Why don't others see that this is all relative. For example I was observing Achird the other night. In order to enjoy the view, do I need to bring out the most extreme large aperture I've got? I just don't get some of the posts in these forums sometimes regarding this constant beating about observers gotta have the largest telescope for everything they look at.

 

 

I use them all.. big, small, exquisite optics, so-so optics.

 

 It is true that all things are relative.. On the other hand, nearly all the doubles that can be split with a 4 inch scope can be split with a 10 inch scope but of course the reverse is not true.  Myself, I spend a lot of time enjoying doubles in my 3, 4 and 5 inch scopes, refractors and Newtonians.  But at the same time, I recognize that my 10 inch generic GSO Dob is a much more capable instrument and that the effort required to set it up is only minimally more than the 4 inch APO so when doubles are the primary meal on the menu, I do make that small added effort and setup either the 10 inch F/5.5 or my 13.1 inch F/5.5 with the R. Royce mirror.  These split doubles, particularly the 13.1 inch that are beyond the capability of any affordable, manageable refractor.  I am an opportunistic observer, I take what the sky gives me... It's not just one double, it's a variety of doubles and they depend on the conditions... I am not setting up with only a single target in mind.. 

 

So I would say this:  I also have a variety of high quality (and not so high quality) scopes to roll out.  If one has easily setup larger scopes, then the question of whether to roll out the larger scope can be "Why not roll it out?" Generally the reason has to do with thermal equilibrium and the possibility of clouds rolling in.. But when I do roll out one of the larger scopes and spend some time observing doubles, I do wonder why I ever bother with the refractors, the larger Newtonians are just so much more capable.. 

 

And that is the focus of this subthread.  All scopes are competent at splitting doubles. And small refractors and small reflectors present the doubles within their capabilities very nicely and without much trouble. But in the big picture, they are limited in what they can do... I use them all but I recognize that their limitations... 

 

I wonder why experienced observers have trouble simply acknowleging that refractors are good for splitting doubles that are within their limits just as they are at viewing galaxies that are within their limits but there are other scopes with larger apertures that are more capable.. 

 

As I said, I use them all.

 

Jon

 

[Sarkikos]

I wonder why experienced observers have trouble simply acknowleging that refractors are good for splitting doubles that are within their limits just as they are at viewing galaxies that are within their limits but there are other scopes with larger apertures that are more capable..

 

Exactly.

 

Mike

[drollere]

Bruce

 

What is the source of the graph and and what is the analysis that produced it.  Under is ideal conditions, if you double the aperture, the finest resoveable detail is 1/2 the size.  If the aperture of scope A is 20% of scope B, the scope B will resolve details 1/5 the size.. that seems inconsistant with the graph.

 

Jon

 

the point of the graph is to start with any arbitrary range of real aperture. within that range, the smallest aperture gives the least resolution and light grasp, and the largest aperture the most of both. then both resolution and light grasp are standardized within the range: the smallest scope has resolution 1 and light grasp near zero, and the largest aperture has a resolution approaching a very small number and a light grasp of 1.

 

the point of the graph is: where do the curves inflect? the resolution inflects sharply and early, but light grasp does not really get going until the aperture is very large -- within the practicable range. if the largest scope you can afford is 1 meter, then you get 95% of that 1 meter scope's angular resolution with an 8" aperture, if you take the minimum useful (say, 1 centimeter) as the basis. within any practicable definition of amateur commercial choice, the graph does not materially change.

 

you might object that the 1 meter scope gets five times the resolution of the 200mm scope, but then you have embarked on the optical theory play with numbers outside of any practicable physical situation as an anchor. for example, i could retort that a strehl of 99.9999999% is a million times better than a strehl of 99.9%. anchors can be useful, especially when they are real objects.

 

jim raised the important point that a larger glass might do better than the same sized mirror; i looked at light grasp and not throughput. accommodating his point, there would be two curves for objective design, but the resolution curve would stay the same.

 

as a double star astronomer i side bill and the rest who connoisseur their airy disks. the idea of looking at a double star and *not* seeing the airy disks is charming because it indicates an observer working within the lower range of magnification -- in the kingdom of wide field light grasp.

[drollere]

a general comment i would make, something of a community segmentation, is that opinions tend to gravitate toward one of three extreme positions: the physical appliance, the observable image, and the optical theory.

 

we hear a lot, for example, about how much the central obstruction in an SCT or the coma in an orthoscopic eyepiece matter from the point of view of optical theory, but you find these things take on a different significance from the point of view of the observable image in the physical appliance.

 

some people prefer to emphasize the astigmatic curves in an eyepiece, others want to focus on the eye relief or the sheer mass of the thing. image quality is one thing, the weight of the telescope or the difficulty of guiding it by hand is another.

 

each of the three extreme positions "encounters" the others through a specific cluster of "debates". optical theory and physical appliance? -- RMS surface error, central obstruction, and (of course) "brand". optical theory and observable image? -- airy disk simulation, MTF contrast, exit pupil (*not* magnification). physical appliance and observable image? -- collimation, thermals, tracking.

 

preference in instruments is anchored in the range of actual commercial choices of physical appliances that each of us has available to purchase or select from personal inventory. of course people buy and use scopes because they are exemplary at some visual or digital sensor task, or at some compromise among tasks. they are inherently tools, not solutions.

[BillP]

Well, actually not so well stated since Bill snipped out the last clause of my sentence and you disregarded it. What's baffling to me is how two otherwise intelligent people can have such poor reading comprehension. Again here is my full sentence, unedited:

 

"I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ... or you don't want to bother with the weight and bulk of the larger scope."

 

I think you are missing the fun and taking things too seriously.  The snipped out portion was irrelevant since it did not address the other shortcomings of larger and advantage os smaller that come into play.  So much more to consider rather than simply weight and bulk...the last snipped out point does not address the three points where the smaller scope is stronger that I mentioned.  So as a recast of your sentence with snippet from the other perspective...

 

I don't see the advantage to larger aperture for double stars unless perhaps the seeing is very good - in which case you really should be viewing something else ... unless 1) you don't mind the bother with the weight and bulk of the larger scope (what was snipped out), and 2) don't care about its less than advantageous aspects related to needing high magnification to get an airy disk, and 3) its thermal acclimation issues, and 4) having more challenges with the seeing rather than being able to truely push the optic."

 

Anyway...no reading comprehension issue...let it out on purpose as was trying to debate the other 3 points.  Thought this was a fun exchange...sorry if you took it otherwise. 

[Jon Isaacs]

 

Bruce

 

What is the source of the graph and and what is the analysis that produced it.  Under is ideal conditions, if you double the aperture, the finest resoveable detail is 1/2 the size.  If the aperture of scope A is 20% of scope B, the scope B will resolve details 1/5 the size.. that seems inconsistant with the graph.

 

Jon

 

the point of the graph is to start with any arbitrary range of real aperture. within that range, the smallest aperture gives the least resolution and light grasp, and the largest aperture the most of both. then both resolution and light grasp are standardized within the range: the smallest scope has resolution 1 and light grasp near zero, and the largest aperture has a resolution approaching a very small number and a light grasp of 1.

 

the point of the graph is: where do the curves inflect? the resolution inflects sharply and early, but light grasp does not really get going until the aperture is very large -- within the practicable range. if the largest scope you can afford is 1 meter, then you get 95% of that 1 meter scope's angular resolution with an 8" aperture, if you take the minimum useful (say, 1 centimeter) as the basis. within any practicable definition of amateur commercial choice, the graph does not materially change.

 

you might object that the 1 meter scope gets five times the resolution of the 200mm scope, but then you have embarked on the optical theory play with numbers outside of any practicable physical situation as an anchor. for example, i could retort that a strehl of 99.9999999% is a million times better than a strehl of 99.9%. anchors can be useful, especially when they are real objects.

 

 

 

The inflection points are based on the graph but that's just a matter of how the graphs are drawn, resolution is inversely linear with aperture, a 100mm aperture can resolve objects with 1/2 the separation of a 50mm aperture.. A term like 95% of the resolving power has no real meaning since greater resolution means smaller numbers...

 

 The standard analysis says the Rayleigh Criteria for a 20mm scope is 6.9 arc-seconds while the Rayleigh Criteria for a 100mm scope is 1.38 arc-seconds.  Normally one might call that 5x the resolving power but it is more accurately stated that the 100mm scope is able to resolve objects that are of 1/5th the separation.  

 

Jon

[Sarkikos]

 

Well, actually not so well stated since Bill snipped out the last clause of my sentence and you disregarded it. What's baffling to me is how two otherwise intelligent people can have such poor reading comprehension. Again here is my full sentence, unedited:

 

"I don't see the advantage to smaller aperture for double stars unless perhaps the seeing is very poor - in which case you really should be viewing something else ... or you don't want to bother with the weight and bulk of the larger scope."

 

I think you are missing the fun and taking things too seriously.  The snipped out portion was irrelevant since it did not address the other shortcomings of larger and advantage os smaller that come into play.  So much more to consider rather than simply weight and bulk...the last snipped out point does not address the three points where the smaller scope is stronger that I mentioned.  So as a recast of your sentence with snippet from the other perspective...

 

I don't see the advantage to larger aperture for double stars unless perhaps the seeing is very good - in which case you really should be viewing something else ... unless 1) you don't mind the bother with the weight and bulk of the larger scope (what was snipped out), and 2) don't care about its less than advantageous aspects related to needing high magnification to get an airy disk, and 3) its thermal acclimation issues, and 4) having more challenges with the seeing rather than being able to truely push the optic."

 

Anyway...no reading comprehension issue...let it out on purpose as was trying to debate the other 3 points.  Thought this was a fun exchange...sorry if you took it otherwise. 

 

I hold no grudges. No offense taken, none intended. Those  's in my posts do mean something.

 

Now if the sky clears tonight, I intend to take out the C80ED to look at the Moon, planets AND double stars!  The 10" Dob will take a rest until next trip to a dark site ... maybe.

 

Mike

Edited by Sarkikos, 11 August 2014 - 12:10 PM.

[schang]

Boys, I was simply suggesting that woolly stars in a dob can be cleared up with an aperture mask so that stars or double stars show airy disks, especially for bright stars and close doubles.   

 

I do not take my 10" dob out unless the conditions are at least 3/5.  I used to have also taken out either my C90 Mak or C102 with it, but not any more.  It is either the dob, or the others, because of the 3.75" light weight aperture mask for doubles when I feel like to see the airy disks.  It is also not too shabby in aperture size for splitting most of the double stars, comparing with 60mm, 75mm, or 90mm scopes.  I like this option and it is free.

Edited by schang, 11 August 2014 - 12:45 PM.

[-Starfighter-]

 

Hi All,

 

Admittedly my experience with the small refractor is limited, however I think I have just had an epiphany on these scopes. Although I affectionately call the refractor the 4x4 of scopes due to its ease of use and grab-n-go factor I am starting to think that it is not an ideal scope to separate stars on globular clusters and look for feint fuzzies. ...  I am starting to think if I want to have the impressive views where I can resolve the stars in clusters I am going to have to be at a 8" CAT min. Perhaps I will have to sell it and look for a new set up. I think I am still going to want to have an apo in my collection in the future but I am now skeptical that it's going to be the scope that gets used the most. ...

 

Thoughts?

 

For you...for now...I would agree that it will not get used the most.

 

At the current time in your observing career you are enthralled with globs and DSO...and you like seeing more and more stars in them.  So for that aspect of observing, aperture is what you need to focus on.  And FWIW, when I switch between my XT10 and 8" SCT for similar objects, the 8" is a disappointment.  So I would recommend a plan that includes something bigger than an 8" SCT. 

 

A point that Greg brought up though is that what is often not discussed is how our tastes change.  I have noticed this a lot about myself over the years related to observing.  So one needs to understand that there is no *final* setup, but just the setup that works for now as things will change.  One also has to realize that for targets like globs and faint fuzzies yes more aperture can be the ticket *IF* how you like to observe them is close up and personal.  But if you enjoy studying them from a further out perspective, and have come to enjoy that type of view, then the larger aperture smaller TFOV scopes can be limiting.  As example, M81 and M82 I view semi-often.  When I use the 10" I can make out nice details and structure, and of course mostly looking at them one at a time.  But the view I feel is most aesthetic and therefore the one I choose most often, is using a 6" refractor with a 30mm wide field eyepiece.  So it really does boil down to a person's taste at the time as to which type and aperture of scope is best suited to them.  Our tastes change over time...it's just part of life...and as they do our scopes need to change also.

 

Good Point. I appreciate the recommendation. My only problem being finding a good alt-z mount that will carry the 10" CAT. In addition I am trying to keep the set up reasonably grab-n-go.