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put your stars on a diet

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#1 Daniel Mounsey

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Posted 14 September 2018 - 04:32 PM

I gotta pop a cap in this thing once and for all. In-light of this recent thread https://www.cloudyni...ral-refractors/ I decided to do this "visual" experiment over the course of the past couple of nights with a few of my observing buddies, DarrenT, David Person and mikona who are also members here on CN. I wanted to gather their opinions to see if they agreed or not and overwhelmingly they were blown away at the results. This is very common knowledge among many seasoned double star observers, yet there's still an astonishing amount of experienced observers who are still under the impression that larger aperture is literally "always" better and that concept just blows me away. I have noticed that whenever I discuss this in the double star forum, many observers understand it and really get it, yet whenever I post this in the refractors forum, It's almost always met with skepticism.

 

To me there are many myths in astronomy like, how important it is to have dark skies, yet 80% of where I enjoy my observing is in light polluted skies. For example, Alvin Huey and Don Pensack love to observe faint fuzzies and I totally get that. If I was into faint fuzzies more, I'd use a big Dob and find the darkest skies possible to see them. We all know that term "clear skies". Read any of my posts and you will rarely ever see me write "clear skies". My signatures almost always read "steady skies" because most of what I care about is steady air. I absolutely despise bad seeing with a passion. I'll take light pollution just fine, but I absolutely dread bad seeing because everything I love to observe relies heavily on steady skies. Just recently, I was viewing double stars in a really dark sky. At higher magnifications, I actually found it slightly annoying because it makes it harder to frame carbon stars and double stars in the center of the FOV because I can hardly see the field-stop of the eyepiece which I use to frame stars. I totally get it if others want their dark skies, but they're really not needed for everything observers look at and I think there's still a countless number of observers who still don't really quite understand this concept. I often keep ambient lights around me in the yard which are kept on constantly while I'm observing the solar system, Moon and certain stars and that's how I prefer it for several reasons which I've shared in other threads. There are some advantages to these methods and some disadvantages. I know that's hard for countless observers to believe, but it's true.

 

But, let's get back to those useless smaller apertures so many others are convinced of. Have a look here. How could anyone use a petty 3" telescope? It's not big enough you say, but that's just really bad information when someone gives you that impression. If anything, it merely reflects their own lack of personal experience on what a small lens is actually capable of showing them.

 

https://www.cloudyni...telescope-r1874

 

So, let me put this in bold letters so it's actually more clear. There are many instances where increased aperture is actually a hindrance to images. I have a 60mm, 90mm, 102mm, 128mm, 152mm, 250mm. There are countless targets the smaller 60mm refractor will literally and clearly outperform all of the larger apertures. I've sometimes asked myself why Burnham's Celestial Handbook has been such a goldmine to me over these past 25 years and I've come to realize it's because Burnham gave so much attention to individual stars. Robert Burnham Jr. was a 20th century jewel. It's a companion with lists that read like this....

 

1.) LIST OF DOUBLE AND MULTIPLE STARS
2.) LIST OF VARIABLE STARS
3.) LIST OF STAR CLUSTERS, NEBULA, AND GALAXIES

 

When I read deeper into that, some interesting thoughts come to mind. The first thing is that I can observe categories 1 and 2 from the convenience of my light polluted skies perfectly fine. The only time light pollution is of a hindrance is if the targets are too faint, but don't forget, there are countless targets that are not too faint or unresolvable in smaller apertures which can be studied and observed. Still, many insist that astronomy isn't enjoyable unless it's under dark skies. For the vast majority of beginners who are primarily looking at showpiece objects like M13 and M31, of course darker skies help, but you have to remember that observational astronomy is not always about deep sky targets like those listed in category 3.

 

The late great Leslie Peltier who wrote "Starlight Nights" observed over 100,000 variable stars said this about his 6" and 12" achromatic refractors. "Each telescope has its own particular sphere of usefulness. Each one can perform its own specific duties much better than could the other one, so there is really no cause for any rivalry between the two and I, for my part, have always done my best to insure domestic tranquility by alotting them equal observing time". Those were the words of a very wise and extremely experienced observer, so if anyone tells you aperture is a must, ask them if they've ever observed 100,000 variable stars before.

 

Okay, so let's get back to this aperture thing, shall we? You have a few options. You can take one large refractor and use a couple of different aperture masks as if you had several refractors of different aperture, or if you don't feel like lugging out a big scope and masking it down, then set up a 60mm achromatic or ED lens or a portable 80mm lens. I assure you, you will have a blast if you know what you're doing. The problem is many observers don't understand what targets look best in certain apertures because they're probably just into deep sky showpiece objects and are not familiar with this. The other problem is knowing the limits of your telescope and this is also where the problems stem from. Another issue is countless observers have the incorrect perception that every double or multiple star you want to see has to be the tightest double. Ahhhhhh..... I gotta have a telescope that splits the tightest doubles obtainable and that means its a better telescope for doubles. If you think that, then you're missing the boat. Let's just do some basic stuff. We'll just use the common Dawes limit. 4.56 divided by your aperture in inches.

 

2" aperture 2.2"
5" aperture .9"

 

Okay, set your parameters for your 2" telescope. Select doubles that are about 3 arc seconds or more. Just select doubles that are above or close to the Dawes limit of any aperture. Also, for a 2" or 3" glass, select brighter doubles like 0 to 8th magnitude that are typically your showpiece doubles. I used my FS128 which comes with a dust cap that has about a 2" aperture opening that simply unscrews from the center of the cap. The target chosen for this demonstration was Alpha Hercules "Rasalgethi". Here's some info on this double. We looked at about two dozen showpiece objects but I'm just using this one for explaining this. There are many more.

 

http://www.perezmedi...ves/001394.html

http://stars.astro.i...rasalgethi.html

 

For this comparison we used 104x and 173x with a 10mm and 6mm Ortho and my 1.25" Tak prism diagonal. Seeing looked pretty good but not great because we were in the valley. At 128mm full aperture, Rasalgethi appeared like the images you see here in Pickering 4 and 5. The two stars also looked a bit over exposed, so the colors did not appear as distinct as we would have desired or have seen in the past. In other words, they were slightly washed out from the seeing. The separation and magnitude of these two stars is also within the grasp of each aperture. I then placed the small mask over and the differences were incredible to say the least. Several things changed and I let the guys decide what they liked after we all compared the two images.

1.) With the 2" aperture applied, the airy disks looked larger and clearly more distinct due to the decrease in resolving power. At 5" aperture, the airy disks appeared smaller, brighter, noisier like Pickering 4 and less colorful.

2.)  At 2" aperture, all the scintillating was clearly reduced. The brighter component looked like Pickering 8 and 9 while the secondary component looked like Pickering 10 in fact we could only see a very slight diffraction ring around the primary while the secondary was nonexistent altogether. In other words, just two textbook pinballs that looked absolutely breathtaking.
3.) All of us overwhelmingly agreed the colors were clearly more obvious and distinct in the smaller 2" aperture and less over exposed looking like they were at 5".
4.) mikona was especially in awe at this because he was not aware that this is what happens when you reduce aperture for many double stars. mikona also has a SkyWatcher 120ED and when I came over to explain what we were doing, he realized that his telescope also has about the same size aperture opening which can easily be removed from the front dust cap. He later also swung over to Mizar and Alcor with the 2" aperture and dropped his jaw in disbelief at how beautiful and perfectly textbook the images looked.

 

This then taunts the next question. Many observers will swear stars are more colorful in larger apertures but that's not the only way works. There's a big difference between stars and extended objects like planets and planetary nebula for example. Certainly in those cases, the larger apertures will usually provide you with increased color contrast, but stars are another story. These points of light can often easily appear washed out or over exposed looking in appearance while reducing aperture increases and exposes the airy disk. This in turn makes the stars appear almost immune to some seeing conditions compared to larger apertures. The result is that you can see solid distinct disks with colors displayed more easily. This taunts another question still. Many observers will say that seeing affects apertures the same way. My suggestion is to cut yourself a cardboard aperture mask 80mm to 60mm from a cereal box and see for yourself and you be the judge. I hope others aren't stuck in bad weather, otherwise I'll probably never hear the end of their stat sheets.

 

Some of the guys laugh when I set up the tiny Takster which is about the size of a fetus, but I can tell you this much, I'll have a pretty good idea what I'm pointing it at and it's highly unlikely that whatever it is will look better in anything larger. Pick your mission and as with all things, everything is relative. Put aside your strong biases and check out some breathtaking showpiece doubles. For me, I love to see clean and crisp textbook images when I can. I'm happy to hear your impressions.

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Edited by Daniel Mounsey, 14 September 2018 - 11:12 PM.

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#2 paul m schofield

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Posted 14 September 2018 - 05:16 PM

Thank you, Daniel, for this enlightening article. You have renewed my interest and drive for using my 80mm under my gray zone suburban skies. Close to the beach here in S. Florida the skies are usually very steady so I'm going to concentrate more on double and multiple stars. I still use my out-of-print Edmund Scientific Mag 6 Star Atlas because of the wonderful lists of double and variable stars as well as DSO's that accompany the star charts as well as Sky Safari on my iPad. Thanks again.

Steady skies, :-)

Paul
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#3 CSG

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Posted 14 September 2018 - 05:19 PM

What a terrific post!  Well done.

 

Signed,

 

small refractor fan


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#4 Cpk133

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Posted 14 September 2018 - 05:49 PM

Couldn't agree more with your thesis.  A 60mm refractor puts up a beautiful display under just about any conditions.  I really appreciate the color fidelity of a minimally effective aperture on doubles.  Put another way, the scope that just splits splits best.


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#5 Edrow10

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Posted 14 September 2018 - 05:49 PM

Excellent write-up Daniel. bow.gif  waytogo.gif

 

Best,


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#6 Redbetter

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Posted 14 September 2018 - 05:50 PM

When I read the title "put your stars on a diet" I figured it was a coin flip as to the direction of thrust of the article:  smaller aperture equals larger (fatter) airy disks, while larger aperture results in smaller but much brighter airy disks.  Diet could refer to brightness or angular size.

 

For stars if one wants to get the "best" aesthetic view, one needs to match the aperture to the magnitude(s) of star(s) chosen, and to conditions.  The same is true for getting the best sensitivity to estimating magnitudes.   And when it comes to color, the tones become warmer with smaller aperture at high power--that can be good or bad depending on circumstances.  There is a Pandora's box of questions about color perception as one goes to higher magnification and very small exit pupils--consider the changing color of the Moon in small aperture as one does this.  There is no one size/tool fits all with respect to targets or observers. 

 

Yes, stars nearer the limits of an aperture look cleaner even in poor seeing (for the aperture) because about all one is going to resolve is the central brightness.   The rings of dimmer stars disappear, being too diffuse to see next to the brighter central portions of the disk.   

 

The bright skies vs. dark skies comment with regards to seeing the field stop at high power is something I have explored (mostly in dark sky) with respect to determining where the background becomes fully black.  For my eye this is typically in the ~0.4mm exit pupil range in dark sky with refractors (and reflectors.) 


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#7 Sketcher

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Posted 14 September 2018 - 06:00 PM

Usually when I hear the term "diet" it's used in the context of slimming down . . . making less fat.  Obviously you're wanting to put the stars on rather fatty diets to make them bigger!  "Fatten your Stars" would be my alternate title . . .

 

But yes indeed, many doubles are aesthetically more pleasing with smaller apertures.  I have a 4-inch SCT that can't compete in most categories with my larger scopes; but it's outstanding with double stars!  The smaller aperture (along with some 'lucky' high quality optics) shows high-quality airy disks more often.  The largish central obstruction provides a helping hand by pumping a bit more light into the first diffraction ring -- enhancing that 'ring around the star' effect.  So when I want to observe some suitably wide, bright doubles; that scope is a good choice.

 

And yes, suitably chosen doubles are indeed beautiful when observed with smaller refractors.  Well defined airy disks are encountered far more often when one is using smaller aperture telescopes.

 

I have aperture masks made in 10mm increments, from 10mm up through full aperture, for my two largest refractors.  Now I guess I'll have to use them a bit more often! smile.gif


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#8 GoFish

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Posted 14 September 2018 - 06:04 PM

Extrapolating, could one conclude there exists a set of stars best viewed naked eye?


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#9 Redbetter

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Posted 14 September 2018 - 06:35 PM

Extrapolating, could one conclude there exists a set of stars best viewed naked eye?

Unfortunately, most of us have less than perfect vision, rendering the stars "fatter", pointier, etc. than if one used an equivalent aperture (say 7mm) at a smaller exit pupil (e.g. 1, 0.5, etc.)  Comparison to binocular vision complicates matters as well...

 

While I can still see stars to 7.0 NELM in dark sky, I can also see DSO's to ~7 NELM in dark sky as well.  When I was younger and my vision was better I regularly went 0.5 mag deeper for stars.  Presently 6.5 to 7 mag stars and DSO's become effectively indistinguishable in appearance to my naked eyes, because of the defects of my "20/20"(according to my recent eye exam) vision.  Fully focused for distance in a scope with 7mm exit pupil they are much sharper, but still show some astigmatism.  At small exit pupils the astigmatism disappears as well.



#10 Mike W

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Posted 14 September 2018 - 06:58 PM

The last couple years I've been mainly into double stars using my Televue 102 but where I live the seeing isn't often that good (northeast) so thanks for this article! I'm going to make a couple ap. masks.

Mikewaytogo.gif 


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#11 Jon Isaacs

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Posted 14 September 2018 - 08:00 PM

A few thoughts:

 

- I am one who spends a lot of time observing double stars.  My San Diego backyard is close to the ocean and the seeing is quite often quite good so splitting sub-arc-second doubles is often doable. 

 

- The Dawes limit is not an aesthetically pleasing split.  The Rayleigh criteria is not an aesthetically pleasing split,  the disks are still over lapping. I think a "clean split" is something closer to twice Rayleigh limit, the first minima overlap. 

 

- As Daniel says,  there's doubles for every scope.  There's doubles for my 60 mm F/5 achromat,  there's doubles for an ST-80, there's doubles for an A-P 60 mm F/13.3 (Asahi -Pentax), there's doubles for a 10 inch F/5 and for Red's 20 inch F/5. And doubles for every scope in between.  

 

I enjoy them all but I am most taken on those nights when the seeing cooperates and close doubles that are at best barely splittable in a normal refractor are clean and wide in my $240 on Astromart 10 inch GSO Dob.  

 

Refractors are easy scopes , you pay your money and they just work. That's OK for some and I enjoy my refractors. 

 

But I'm a tinker at heart.  I spent my life in a laboratory making difficult measurements,  devising techniques, schemes and equipment to make measurements that had not been previously possible. I enjoy pushing a system to it's limits,  getting the most out of it that's possible.   

 

Double stars represent an optical limit, a challenge,  the bigger the scope,  the more difficult the challenge.  Making a Dawes limit split with my $240 on Astromart 10 inch GSO Fob,  that's my kind of fun. So, those nights when the skies are rock solid steady,  those are the nights for messing around with a larger aperture Newtonian. 

 

Other nights,  other Scopes.  Recently I've been spending a fair amount of time with my Meade 310. It's a Mizar made 80 mm F/11 achromat.  Does a good job on doubles without being overly long.   

 

I think the main thing is discovering what you enjoy and then doing it.  I enjoy deep sky so I spend a week or two a month under reasonably dark skies hunting down faint fuzzies. And otherwise,  I enjoy the planets and doubles whenever the skies are clear. 

 

At this point in my observing career,  the aesthetic aspects are not at the top of my list of priorities but there are some doubles that captivate me.  I can stare at them for an hour .  Alula Australis is one..  

 

Enough rambling. 

 

Jon


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#12 Jeff B

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Posted 14 September 2018 - 08:08 PM

Right arm and outta sprite Daniel-san!  I tried to "like" your post a few dozen times but I couldn't.

 

This is precisely why all of my big achromats have aperture stops.  And I use them!  People think I'm crazy but I simply say "Stops allow me to better match the aperture to the prevailing seeing conditions".  That is usually followed by the blank stare back at me.  Some actually "get it" though.  But not many.  Until I show them.  Epsilon Lyrae is one of my favorites to do the demo, especially with the 8.25 and, especially, especially, the  11" achromats at the observatories.  Many times I said let's now look at some double stars but first I'm going to stop down the lens to 6".   "WHAT?!" is the reply.  "Here, I'll show you.  See, the double double looks awful, fuzz ball city.  Now look what happens when I apply the 6" stop.  Magic!  Two sets of beady little eyes staring back at us from space.  Which view did you prefer?"  Everyone says that stopped view.  

 

I liken it to an improved signal to noise ratio in hi-fi.  Beyond a certain resolution point for me in audio (volume), I could also hear the noise.  So I backed off the volume.  The noise present in the sound very much depended on how much noise was in the source material.  If it had a lot of noise, increased volume simply unmasked the noise and it started to compete with the music for attention.  I want to listen to music, not noise so I match the volume to the signal.  The noisier the signal, the lower the volume.  The cleaner the signal, the higher the volume.

 

Similarly, with noisy air, I can either back off of the magnification and/or stop the aperture. But if I want to split doubles and see the airy disk without noise, I back off on the aperture.  Also, simply stopping the aperture decreases the exit pupil size which decrease the noise in your eye as well.  Nothing like a two-fer.

 

And I've found stopping the aperture to be of benefit  with noisy air for lunar and planetary viewing as well.

 

Thanks for the great post Daniel-san.

 

Jeff


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#13 LewisM

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Posted 14 September 2018 - 08:41 PM

I kept smashing that like button so hard I need a new mouse.

 

SO many axioms out there in astro-land it's mind boggling. If for example I ever hear the "you can't use an astrograph refractor for visual" dribble again, I'll have a schism.


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#14 Tyson M

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Posted 14 September 2018 - 08:44 PM

I gotta pop a cap in this thing once and for all. In-light of this recent thread https://www.cloudyni...ral-refractors/ I decided to do this "visual" experiment over the course of the past couple of nights with a few of my observing buddies, DarrenT, David Person and mikona who are also members here on CN. I wanted to gather their opinions to see if they agreed or not and overwhelmingly they were blown away at the results. This is very common knowledge among many seasoned double star observers, yet there's still an astonishing amount of experienced observers who are still under the impression that larger aperture is literally "always" better and that concept just blows me away. I have noticed that whenever I discuss this in the double star forum, many observers understand it and really get it, yet whenever I post this in the refractors forum, It's almost always met with skepticism.

 

To me there are many myths in astronomy like, how important it is to have dark skies, yet 80% of where I enjoy my observing is in light polluted skies. For example, Alvin Huey and Don Pensack love to observe faint fuzzies and I totally get that. If I was into faint fuzzies more, I'd use a big Dob and find the darkest skies possible to see them. We all know that term "clear skies". Read any of my posts and you will rarely ever see me write "clear skies". My signatures almost always read "steady skies" because most of what I care about is steady air. I absolutely despise bad seeing with a passion. I'll take light pollution just fine, but I absolutely dread bad seeing because everything I love to observe relies heavily on steady skies. Just recently, I was viewing double stars in a really dark sky. At higher magnifications, I actually found it slightly annoying because it makes it harder to frame carbon stars and double stars in the center of the FOV because I can hardly see the field-stop of the eyepiece which I use to frame stars. I totally get it if others want their dark skies, but they're really not needed for everything observers look at and I think there's still a countless number of observers who still don't really quite understand this concept. I often keep ambient lights around me in the yard which are kept on constantly while I'm observing the solar system, Moon and certain stars and that's how I prefer it for several reasons which I've shared in other threads. There are some advantages to these methods and some disadvantages. I know that's hard for countless observers to believe, but it's true.

 

But, let's get back to those useless smaller apertures so many others are convinced of. Have a look here. How could anyone use a petty 3" telescope? It's not big enough you say, but that's just really bad information when someone gives you that impression. If anything, it merely reflects their own lack of personal experience on what a small lens is actually capable of showing them.

 

https://www.cloudyni...telescope-r1874

 

So, let me put this in bold letters so it's actually more clear. There are many instances where increased aperture is actually a hindrance to images. I have a 60mm, 90mm, 102mm, 128mm, 152mm, 250mm. There are countless targets the smaller 60mm refractor will literally and clearly outperform all of the larger apertures. I've sometimes asked myself why Burnham's Celestial Handbook has been such a goldmine to me over these past 25 years and I've come to realize it's because Burnham gave so much attention to individual stars. Robert Burnham Jr. was a 20th century jewel. It's a companion with lists that read like this....

 

1.) LIST OF DOUBLE AND MULTIPLE STARS
2.) LIST OF VARIABLE STARS
3.) LIST OF STAR CLUSTERS, NEBULA, AND GALAXIES

 

When I read deeper into that, some interesting thoughts come to mind. The first thing is that I can observe categories 1 and 2 from the convenience of my light polluted skies perfectly fine. The only time light pollution is of a hindrance is if the targets are too faint, but don't forget, there are countless targets that are not too faint or unresolvable it smaller apertures which can be studied and observed. Still, many insist that astronomy isn't enjoyable unless it's under dark skies. For the vast majority of beginners who are primarily looking at showpiece objects like M13 and M31, of course darker skies help, but you have to remember that observational astronomy is not always about deep sky targets like those listed in category 3.

 

The late great Leslie Peltier who wrote "Starlight Nights" observed over 100,000 variable stars said this about his 6" and 12" achromatic refractors. "Each telescope has its own particular sphere of usefulness. Each one can perform its own specific duties much better than could the other one, so there is really no cause for any rivalry between the two and I, for my part, have always done my best to insure domestic tranquility by alotting them equal observing time". Those were the words of a very wise and extremely experienced observer, so if anyone tells you aperture is a must, ask them if they've ever observed 100,000 variable stars before.

 

Okay, so let's get back to this aperture thing, shall we? You have a few options. You can take one large refractor and use a couple of different aperture masks as if you had several refractors of different aperture, or if you don't feel like lugging out a big scope and masking it down, then set up a 60mm achromatic or ED lens or a portable 80mm lens. I assure you, you will have a blast if you know what you're doing. The problem is many observers don't understand what targets look best in certain apertures because they're probably just into deep sky showpiece objects and are not familiar with this. The other problem is knowing the limits of your telescope and this is also where the problems stem from. Another issue is countless observers have the incorrect perception that every double or multiple star you want to see has to be the tightest double. Ahhhhhh..... I gotta have a telescope that splits the tightest doubles obtainable and that means its a better telescope for doubles. If you think that, then you're missing the boat. Let's just do some basic stuff. We'll just use the common Dawes limit. 4.56 divided by your aperture in inches.

 

2" aperture 2.2"
5" aperture .9"

 

Okay, set your parameters for your 2" telescope. Select doubles that are about 3 arc seconds or more. Just select doubles that are above or close to the Dawes limit of any aperture. Also, for a 2" or 3" glass, select brighter doubles like 0 to 8th magnitude that are typically your showpiece doubles. I used my FS128 which comes with a dust cap that has about a 2" aperture opening that simply unscrews from the center of the cap. The target chosen for this demonstration was Alpha Hercules "Rasalgethi". Here's some info on this double. We looked at about two dozen showpiece objects but I'm just using this one for explaining this. There are many more.

 

http://www.perezmedi...ves/001394.html

http://stars.astro.i...rasalgethi.html

 

For this comparison we used 104x and 173x with a 10mm and 6mm Ortho and my 1.25" Tak prism diagonal. Seeing looked pretty good but not great because we were in the valley. At 128mm full aperture, Rasalgethi appeared like the images you see here in Pickering 4 and 5. The two stars also looked a bit over exposed, so the colors did not appear as distinct as we would have desired or have seen in the past. In other words, they were slightly washed out from the seeing. The separation and magnitude of these two stars is also within the grasp of each aperture. I then placed the small mask over and the differences were incredible to say the least. Several things changed and I let the guys decide what they liked after we all compared the two images.

1.) With the 2" aperture applied, the airy disks looked larger and clearly more distinct due to the decrease in resolving power. At 5" aperture, the airy disks appeared smaller, brighter, noisier like Pickering 4 and less colorful.

2.)  At 2" aperture, all the scintillating was clearly reduced. The brighter component looked like Pickering 8 and 9 while the secondary component looked like Pickering 10 in fact we could only see a very slight diffraction ring around the primary while the secondary was nonexistent altogether. In other words, just two textbook pinballs that looked absolutely breathtaking.
3.) All of us overwhelmingly agreed the colors were clearly more obvious and distinct in the smaller 2" aperture and less over exposed looking like they were at 5".
4.) mikona was especially in awe at this because he was not aware that this is what happens when you reduce aperture for many double stars. mikona also has a SkyWatcher 120ED and when I came over to explain what we were doing, he realized that his telescope also has about the same size aperture opening which can easily be removed from the front dust cap. He later also swung over to Mizar and Alcor with the 2" aperture and dropped his jaw in disbelief at how beautiful and perfectly textbook the images looked.

 

This then taunts the next question. Many observers will swear stars are more colorful in larger apertures but that's not the only way works. There's a big difference between stars and extended objects like planets and planetary nebula for example. Certainly in those cases, the larger apertures will usually provide you with increased color contrast, but stars are another story. These points of light can often easily appear washed out or over exposed looking in appearance while reducing aperture increases and exposes the airy disk. This in turn makes the stars appear almost immune to some seeing conditions compared to larger apertures. The result is that you can see solid distinct disks with colors displayed more easily. This taunts another question still. Many observers will say that seeing affects apertures the same way. My suggestion is to cut yourself a cardboard aperture mask 80mm to 60mm from a cereal box and see for yourself and you be the judge. I hope others aren't stuck in bad weather, otherwise I'll probably never hear the end of their stat sheets.

 

Some of the guys laugh when I set up the tiny Takster which is about the size of a fetus, but I can tell you this much, I'll have a pretty good idea what I'm pointing it at and it's highly unlikely that whatever it is will look better in anything larger. Pick your mission and as with all things, everything is relative. Put aside your strong biases and check out some breathtaking showpiece doubles. For me, I love to see clean and crisp textbook images when I can. I'm happy to hear your impressions.

Thanks Daniel, wise words and I have paid attention. My 80mm will get lots of continued love here. 

 

Cheers from Canada


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#15 Brent

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Posted 14 September 2018 - 08:46 PM

Sink me, Daniel, I couldn't agree more.  I discovered this on my own about a year and a half ago (maybe not quite).  I was comparing the view of Pulcherima through a Tak FS-60Q and a Questar, and found that the colors of the stars were much much more vibrant in the 60mm.  When I posted the results in the Questar forum, one member initially thought I was trolling.

 

But repeating the observations with 4" and 7" confirmed my hunches: the view was still best in the 60mm.  In the smaller scope, the background sky was blacker, so that paired with the larger airy disks, and steadier view emphasized the color of the stars more.  I think I compared the effect to that produced by the tracery in a stained glass window, or the black outlines in a George Rouault painting. Dang, that was pretty.

 

Brent


Edited by Brent, 14 September 2018 - 08:52 PM.

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#16 daveCollins

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Posted 14 September 2018 - 08:48 PM

When I tell people that I observe from Washington DC, the reaction is usually "How can you see anything?". I observe doubles almost exclusively. On nights with steady seeing, the objects can be breathtaking. I always enjoy observing, even when the seeing is off. I've found that in most cases, if I focus on an object for ten or fifteen minutes, I'll be rewarded with brief sub-second steady moments and when they happen it is a thrill.

 

In order to enhance my experiences, I wear noise canceling headphones, I put up a custom made light shield around my viewing area on my balcony, and I wear a hooded viewing "jacket-shirt".

 

I recently posted a comparison of viewing logs, one using a TOA 150 and the other a 130 GTX. The scopes were used on two consecutive days, but only one scope per day. I simply put the log entries for all doubles viewed, which were the same on both nights, side by side. To my surprise, the log entries I wrote at the eyepiece indicated that I had more fun with the smaller scope. It is true that I could see some dim secondaries in the 150 that I couldn't see in the 130, but the aesthetic impact seemed more significant in the smaller scope.

 

By the way, I also share Jon's experience of not always being focused on aesthetics. I like the technical challenge of tight pairs regardless of the aesthetic qualities of the system. It is the thrill of the chase and a sense of doing something difficult that draws me in sometimes. 


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#17 BillP

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Posted 14 September 2018 - 09:13 PM

Daniel,

As always, you show that Knowledge, Skill. and Experience are the only true Kings!  bow.gif


Edited by BillP, 14 September 2018 - 09:14 PM.

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#18 213Cobra

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Posted 15 September 2018 - 01:44 AM

I kept smashing that like button so hard I need a new mouse.

 

SO many axioms out there in astro-land it's mind boggling. If for example I ever hear the "you can't use an astrograph refractor for visual" dribble again, I'll have a schism.

No kidding. I've been at this since 1961, and I'm 30 years into a Takahashi Epsilon 160 hyperbolic astrograph as my main visual scope, more recently supplemented by FSQ85 & 106. OK, I have a LOMO 80/480 f/6, not technically an astrograph but I use it with a TSFlat2. I've heard so many less experienced people over the years dismiss astrographs as "...well, that's really just a camera..." that it proves once again, the rest of the army really can be out of step.

 

Re: OP, Daniel is altogether correct.

 

Phil


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#19 Erik Bakker

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Posted 15 September 2018 - 04:37 AM

Took me forty years of aperture fever to discover that none of the bigger scopes that came along put up a more beautiful view of some objects than my 76 f/12. Daniel's post makes the power of small instruments very clear waytogo.gif

 

My aperture fever has been cured by the beauty of the views offered by small quality scopes. I now appreciate both more: the small AND big scopes. Enjoying each for what they do best.


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#20 rerun

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Posted 15 September 2018 - 07:26 AM

Hi Daniel,

 

Thank you very much for this very intersting report. It was a great pleasure to read . My little FOA60  sits here with a big smirk. I always was happy with my small scopes. But it was great to read some more informations about steady skies and downsized aperture. While I love doubles there is a lot to view for me.

Thank you for this.

 

Clear steady skies  wink.gif

 

Markus


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#21 Scott Beith

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Posted 15 September 2018 - 07:44 AM

Excellent post Daniel.  As an SRF SLAP observer and someone who has never owned a scope larger than 150mm I agree.  I have used much larger scopes and if I was a DSO observer I would definitely want a light bucket and dark skies, but for my observing preferences seeing conditions rule everything.  My 3.25", 4" and 5.1" refractors continue to serve me well.


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#22 Daniel Mounsey

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Posted 15 September 2018 - 09:10 AM

Guys, Thank you all for the very kind responses and constructive comments.

 

 

Extrapolating, could one conclude there exists a set of stars best viewed naked eye?

 

This is actually an interesting question. BillP and I have been discussing this concept more lately and he’s been working on something quite interesting that makes smaller scopes and naked eye observing quite more fun. Some time ago S&T did this article which is pretty cool.

 

https://www.skyandte...stars-07092014/


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#23 Astrojensen

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Posted 15 September 2018 - 10:00 AM

As someone who has used telescopes with apertures as small as 50mm on a regular basis and down to 10mm as an experiment, I can't agree more with the OP. 

 

But I would also like to point out that small telescopes can actually reveal quite a bit of deep-sky objects, even under less than perfect dark skies. My local weather has become quite erratic and clear nights are not as common as they used to be and I often have to take advantage of very short periods of clear skies. This strongly favors small telescopes and simplified setups, which means I've used my 63mm Zeiss a lot more lately than my 12" dobsonian and I've often observed deep-sky in twilight or moonlight, despite having quite dark skies, simply because I couldn't afford to waste what little observing time that bought me instead of waiting for a better opportunity that might be weeks away. 

 

What I have discovered is that even under a mag 3.5 - 4.5 sky, meaning one where the Milky Way in Cygnus, high overhead, is not visible or just coming into view, even a 60mm allows surprisingly good views of a frankly startling number of objects, provided that you know what you're doing. And if you're living under severely light polluted skies in a major urban center, taking a 60mm to a mag 4 sky can be orders of magnitude easier than taking a 12" to a mag 6 sky. It can mean the difference between an easy half-hour drive and a multiple-hour expedition. Of course it's fun to go to really dark skies, but if it takes four or five hours to do, it's not something you do on a normal evening when you have to get up at five the next morning to go to work. 

 

Obviously, observing deep-sky under such conditions with such a small telescope takes a completely different mindset than observing under dark skies with a 12". A lot of objects that are easy in a 12" will be a challenge merely to detect, but that in itself is fantastic workout and training for when the clear, moonless weekend finally arrives and you can take the 12" out to the state park natural reservation and observe all night for two nights. 

 

I know this is old hat to a lot of people, but I also frequently encounter people that seem not to be aware of how much is possible under less than ideal conditions, if you give it a serious go. And lots of people everywhere seems to just automatically dismiss the idea that small scopes can show anything worthwhile at all. A small scope under bright skies? A waste or time, surely. Wrong! Nothing could be further from the truth. 

 

 

Clear skies!
Thomas, Denmark


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#24 Daniel Mounsey

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Posted 15 September 2018 - 11:28 AM

Thomas, I completely agree in fact I had listed a number of interesting deep sky objects in the several refractors forum, so, hopefully that will add some encouragment to small scope users like myself and many others.  


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#25 JimP

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Posted 15 September 2018 - 05:18 PM

Lovely post Dan. I have said many times, the most beautiful view of doubles I have ever had was with a Quantum 4, a 4” Maksutov. Gorgeous views. Nice crisp airy discs, beautiful colors. Lots of Questar 3.5 scopes out there which would do the same. I like my larger aperture refractors observing the Moon and planets but have an AP 130 F/8.35 on the way specifically to observe doubles. I might try an aperture mask on occasion just to see what results I get. Any thoughts on producing aperture masks that pose no risk to the objective lens?

 

Tuesday, September 18, I will have been observing for 50 years.

 

Good job Dan!


Edited by JimP, 15 September 2018 - 05:33 PM.

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