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resolution limit for binos?

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#1 jmoore

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Posted 12 April 2004 - 11:17 AM

So, Rayleigh's limit tells us how close of a double-star we can split for given aperture, but this assumes the necessary magnification. With binoculars, magnification doesn't allow us to resolve to the full potential of our aperture. So, the question is, how close of a double-star pair can we split with binos?

Assume tripod mounted.

Answer for say, 10x, 15x, and 20x.

Given that we can just about spit the smaller Trapezium pair with 15-16x binos, I'm thinking the resolving power of 15x binos is right around 9"?

thanks,
jeff

#2 EdZ

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Posted 12 April 2004 - 12:21 PM

I'd put the resolving power of 15x up higher.

I once recorded seeing the two components of Gamma Delphinus (9.6") with my 15x70s, but did not split them. I did (only once) split Gamma Del with the 16x70s.

Best record of a slpit with my 15x70s is 13.4" double in Lyra.

I suspected both components of the 8.7" of the Trap once with my 16x70 Fujinon. I did split the 8.7" components with 20x80s.

I did suspect a split of 100 Herc (14.2") once with my 8x42 Swift.

I've never succeeded with a 7.1" (Struve 953) split with my 16x70s. I may have once split it with 20x80s.


Notes from a previous article (2003)
I recently spent a month using binoculars at 10x, 15x, 16x and 20x to find the limit of each binocular by testing the splitting of doubles. I found that at 10x50 the limit was about 20", but at 16x80 or 15x70 the limit was 13" or 14". I had my greatest success with doubles that were close in magnitude. Where the magnitude varied a lot (+2.5) between the primary and the secondary, the difficulty factor increased the limit by 5" to 10".

With my 10x50 Ultraviews I have split doubles at 22" Alya-Ser, 21" 61-Oph and 20" 24-Com. With the 12x50s I split 100-Her 5.9-6.0/14.2” and E2738 Del 6.6-8.7/14.9” appeared elongated. With 15x70s successful targets were E(sigma)2474 Lyr at 16.2" and 100Her at 14.2". With 16x80s I split E2474, 100Her and also E2470 at 13.4".

I've since improved only slightly on some of those noted.


There are at least a half dozen other threads in the binocular forum with a record of some splits and a few lists of doubles targets for binoculars. Search in binoculars on doubles. Also, look in the doubles forum for "doubles for binoculars". Also, go to the "Best of binoculars" and look up resolution.

edz

#3 jmoore

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Posted 15 April 2004 - 11:24 AM

Last night, with my 15x70 Burgess, I cleanly (or very nearly) split Struve-1121, which is within M47 in Puppis. Separation is listed at 7.4". I seem to recall magnitude of both stars as somewhere around 7 (can't recall for sure though).

So...this gives me an idea of a partial answer to my own question. I'd say this double was right at/near the limit of what my 15x70 binos can do.

#4 EdZ

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Posted 15 April 2004 - 11:51 AM

Jeff,

I just recently posted on this same target. I'm pretty good with doubles, as I practice a lot. I view doubles every time I have a piece of equipment outside. I've managed to see down to apparent separations of around 150 arcseconds several times and even once down near 140. But this particular double, I was not able to see with Fujinon 16x70s or 20x80 Standards. It took 24x with the BT100 to see this one. That's not too bad at an apparent separation of 24x7.4 = 168.

For well over a year, I've been gathering information on splitting doubles from some of the most prolific doubles observers that frequent the internet. In the information I've gathered, not a single observer on any target with any scope available, let alone binoculars, has ever recorded splitting a double to an apparent separation of 15x7.4 = 111 apparent arcseconds. Inge Shauvik and (I think) Warren Bitters both have recorded observations of elongation of components down to apparent sizes of 120 to 130 arcseconds.

This excerpt shows the limits I've reached with these various binoculars after hundreds of observations.
The 20x80s split the double star (gamma) y 12 Delphinus 4.5-5.5/9.6”. The 15x70s show y Del as elongated with proper orientation noticeable, but not split. The Oberwerk 20x80s and the Fujinon 16x70s show Sigma 953 Mon elongated with proper orientation noticeable. E953 Mon is 7.2-7.7/7.1”. I noticed this with the Fujinon when I was viewing the Christmas tree cluster. These same three binoculars regularly resolve 3 stars of the Trapezium in M42 and on occasion the 4th was suspected in the Fujinon 16x70s and Oberwerk 20x80s. Finally, on an exceptionally still clear night, the AB component at 8.7” was resolved in the 20x80s at full aperture and also at 20x50. The 20x provided just a bit more magnification that allowed easier splitting of close doubles than could be accomplished with the 16x70s or the 15x70s.

I'm questioning this one Jeff. I don't think it's physiolgically possible. At the very least, it's highly improbable. But there is always the exception.

All of that said, couuld it be that you have superior acuity? I believe you showed once before that you were able to achieve exceptional results on another test.



edz

#5 jmoore

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Posted 15 April 2004 - 04:36 PM

Hi Ed...

I'll answer first, in my defense, and then open myself to the possibility of my error...

In my defense, I do think I have good visual acuity. I haven't done too many formal tests yet...so I have no idea what's normal and what's exceptional...but I know I can see things in my scope that friends standing next to me cannot, especially when it comes to fine planetary detail...(granted, I have more viewing experience than them, so this is to be expected)....

The earlier example of which you speak concerned seeing the Cassini division in small scope at low power. I believe I said I saw it around 50x in my 80mm scope. There was no question on this.

And I know I can see 4 stars in the Trapezium at 16x in my 80mm scope (haven't tried in my 15x70s yet).

Nevertheless, I acknowledge I could be wrong on this one. It's entirely possible I viewed a different double last night, as I didn't have an atlas in hand with me at the time. I was merely looking for M46 and M47 (as you suggested, Ed...found M47, but couldn't see M46 from my backyard). After looking at M47 for awhile with binos, I looked at it with my 5" Mak, and noticed a beautiful double more or less in the middle of the brighter cluster-stars. Then, I put the 15x70s back on M47 to see if I could still split it (whatever it was), and yes, I could...barely...or at least the split was *nearly* clean. Let's just say there was no question it was a double-star...

THEN...I went inside to look at an atlas and determine which double I'd seen. Based on its characteristics (equal magnitudes for A and B, very tight, whitish) and its location (within M47), I concluded that I must have seen Struve-1121...

...but I concede I'm not positive on the ID here. I'm just assuming the identity of whatever I saw. Is there another double with similar description (relatively bright...similar magnitude members...very tight at 15x...more or less in middle of M47) that I might have seen instead?

#6 jmoore

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Posted 15 April 2004 - 04:50 PM

Another possibility, Ed, is that I am correct in my identification (e.g., I did see Struve 1121), but am mistaken in thinking that I cleanly split it. Afterall, it's hard to tell sometimes if you can really see that thin black line or not. But i DO know that it was elongated (and even peanut-shaped) with proper orientation...it was very clear that i was observing a double.

#7 KennyJ

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Posted 15 April 2004 - 05:01 PM

Jeff,

I suppose another possibility ( at least from where I'm sitting ) is that Burgess sent you a 25 x 100 instead of a 15 x 70 , and forgot to tell you ! :-)

Regards , Kenny.

#8 jmoore

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Posted 15 April 2004 - 05:05 PM

wouldn't that be grand...and they're not even very heavy to hand-hold!!
;)

#9 EdZ

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Posted 16 April 2004 - 07:48 AM

I tried this target againn last night.

I started from lowest power to highest.

16x70 Fujinon show elongation. No hint of separation

20x80 Oberwerk Standards show elongation clearly. Suspect a hint of separation.

25x100 shows separation, but need to look past slight glare/flare to see it.

Having seen it in the 25x100s, it comfirmed the 16x70s had the elongation in the proper orientation.


You could very well be seeing the proper star elongated and oriented correctly with 15x70s. Check again a few times see if you can really split it. If so, do as I think Kenny said once before, Donate your eyes to science, but only after you're done with them.

edz

#10 jmoore

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Posted 16 April 2004 - 08:46 AM

Hi EdZ...

checked on this again last night. I was definitely looking at the right pair...

I split it cleanly at 21x with my 80mm scope (using 24mm Konig). No question.

In 15x70 binos...I don't think I could split it. Elongation and orientation was there, but split was not. However, conditions last night were not nearly as good as the night before. Last night was very hazy...some thin high clouds...non-transparent skies. The stars were dim last night...I probably only saw half as many in M47 as the night before.

I will keep trying in good conditions, and let you know.

Funny...I think I do have good eyes in terms of visual acuity, but I have terrible vision. I wear strong eyeglasses. BUT, I don't have astigmatism, so I can view through scope/binos without glasses. I guess visual acuity and "vision" aren't related.

#11 jmoore

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Posted 18 April 2004 - 01:08 PM

Got out with the binos again. Tried to split Struve 1121 with the 15x70s. Don't think I could do it, though again, conditions weren't as favorable as several nights back. By the time clouds had lifted, M46 was getting a bit low...so I was looking through a lot of atmosphere.

So, Ed, I will concede for now! I haven't been able to repeat my ostensible split of this double! But I will keep trying!
;)

cheers,
jeff

#12 EdZ

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Posted 18 April 2004 - 01:44 PM

Try this one Jeff,

Struve 1245 at RA8h40 +7°n. it's on the very lower boderline of Cancer, about 1° nnw of the head of Hydra. It's 6.0-7.2 / 10.3"

I've seen it easily at 25x but only elongated with correct PA using 16x70 Fujinons.

edz

#13 jmoore

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Posted 18 April 2004 - 03:19 PM

will do...
:waytogo:

#14 BarrySimon615

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Posted 18 April 2004 - 05:12 PM

Collimation has a large impact on binocular resolution limits. In addition to vignetting, which has been discussed here recently; collimation greatly affects performance. Unfortunately collimating a pair of binoculars ofter requires a tradeoff. Working together as a team, one or both barrels may sacrifice individual performance to do this. The best collimation for binoculars is one that in collimating the binoculars does not throw individual barrel collimation out of whack too far.

In 1992 I came back from the Texas Star Party with two TeleVue Genesis 4" apo telescopes (both purchased used there). One was really one of two prototypes (Serial # 1001) previously owned by the sales manager at TeleVue. It yielded an excellent image. The 2nd was a later model with retractable "white" dew shield. While excellent, comparison proved that the first scope produced a better image and could hold power a lot better. Double stars were more cleanly split in the first scope. While the second one was no slouch, it just was not as good.

Checking both telescopes with a Cheshire collimating eyepiece uncovered the reason why - the first scope was "spot on perfect" while the second one was just a little off. Unfortunately there is no easy way to "home" collimate a TeleVue, as both objective cell and focuser are not adjustable by the end user.

I have used my Cheshire collimating eyepiece to check collimation on potential purchases and to occasionally tweek collimation on scopes that need it. Later Unitron refractors (early to mid-70's on) have 3 collimating ears as part of the objective cell. These scopes are very easily collimated to a very high level.

When collimated, the Chershire eyepiece will show multiple reflections inside a capped tube with light entering via a cutout in the Cheshire. When collimated, the light path shows itself as multiple concentric overlaid bulls eyes. When not collimated, the bulls eye pattern is not concentric, often looking like "Olympic Rings".

I am posting a photo of a Unitron refractor both collimated and not. I am also posting a picture of the light path image when the Cheshire is used in my Miyauchi 20x100's. Note, the Cheshire substitutes for the telescope or binocular eyepiece. As you can see, the binocular image is not perfect, in fact, I would say it is bad. These are factory collimated, one barrel to the other. As binoculars they are collimated, no double image, and at low powers, 20x, 26x, and 37x the image is good. I do believe that the individual barrel collimation would greatly affect resolution. Perhaps not noticeable at low powers, but very much so at higher magnifications. This tends to prove a major reason why binoculars do not have the resolution capability of telescopes and why some binoculars that come with interchangeable eyepieces, do not work well with their high power eyepieces. Many times, one barrel may be strikingly better than the other barrel, perhaps because in and of itself, one barrel has relatively good individual collimation and the other barrel is quite poor. Comments?

Barry Simon

Attached Thumbnails

  • 92915-Collimation Comparisons.jpg


#15 KennyJ

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Posted 18 April 2004 - 06:23 PM

Barry,

My only comment upon first reading is :

"What a highly informative and extremely interesting post"

I have a feeling you are a person from which many of us could learn a great deal.

Regards , Kenny.

#16 jmoore

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Posted 19 April 2004 - 10:05 AM

Ed...

I got out last night to look for Struve 1245 in Cancer. Split it cleanly in my 15x70s. It was tough though...mainly because of conditions...windy with poor seeing....

At first, I couldn't split it. Conditions were working against me...slight image shake, etc. So, I mounted my 80mm scope, and started at 32x (16mm Konig)...no problem splitting it there. Backed down to 21x (24mm Konig)...also not very difficult. Backed down to 16x (32mm Plossl), and it was still pretty clean. Note that stars come to much sharper, finer, pinpoint focus in my refractor than in my Burgess binos, making star-splitting easier in the scope. But, by this time, the wind had died down a bit, so I tried my binos again, and yes, I could split it...

I am a little worried that after splitting a double at higher mag, it becomes easy to *imagine* splitting it at lower mag because you already know exactly what you're looking for, and it can become tempting to assume success as soon as you catch a glimpse of the truth. Being aware of this potential, however, I made sure to give this double several different looks, separated in time, and with my best effort to be objective. I feel confident in the end, that the split was clean.

jeff

#17 jmoore

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Posted 19 April 2004 - 10:09 AM

As an aside...while I was in Cancer with my 80mm scope, I took at look at the smaller open cluster...M67 or 68...can't remember the name for sure. Very nice...even in my light polluted backyard, I could resolve a lot of stars up around 50x or so. This is a nice, rich cluster...one of the few that I can see *relatively* decently from my light-polluted setting.

In my 15x70s, I could detect it also (fun!), but it was little more than a very very faint smudge. Still, that's more than I can say for most DSOs from my backyard!

#18 lighttrap

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Posted 19 April 2004 - 11:02 AM

I am also posting a picture of the light path image when the Cheshire is used in my Miyauchi 20x100's. Note, the Cheshire substitutes for the telescope or binocular eyepiece. As you can see, the binocular image is not perfect, in fact, I would say it is bad. These are factory collimated, one barrel to the other. As binoculars they are collimated, no double image, and at low powers, 20x, 26x, and 37x the image is good. I do believe that the individual barrel collimation would greatly affect resolution. Perhaps not noticeable at low powers, but very much so at higher magnifications. This tends to prove a major reason why binoculars do not have the resolution capability of telescopes and why some binoculars that come with interchangeable eyepieces, do not work well with their high power eyepieces. Many times, one barrel may be strikingly better than the other barrel, perhaps because in and of itself, one barrel has relatively good individual collimation and the other barrel is quite poor. Comments?

Barry Simon


Fantastic post, Barry. You've nicely illustrated the effects of collimation error in high power binos. That's pretty shocking, isn't it? Do both barrels check out about the same? I'm positive that it was this difference in collimation that led to such bad results in the 1st of 2 Miyauchi NBA 71s that we recently tried. Incidently, the owner of those, reports that they do indeed work at 115x in the 2nd set, but not the first. That would tend to confirm that it was gross miscollimation that was the culprit for the very bad images at 115x in the first set. Do you have any kind of feel for how high you could push the mag in those Miya 100s that you've done the photo with and still not see the effects of miscollimation? How did you do that image? Is it the result of stacking the images from each barrel? I might even add that Chesire test as a standard test of interchangable e.p. binos. Any tips you've got for getting best (worst?) results would be appreciated.

Thanks,
Mike Swaim

#19 EdZ

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Posted 19 April 2004 - 02:57 PM

I was under the impression that each of those photos represent the view thru one barrel.

I considered it an excellent pictoral for the ever present difficulty of how to merge the images and keep the tube collimated.

edz

#20 nemo

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Posted 19 April 2004 - 03:11 PM

Barry,
I would like to compliment you on an excellent post. You seem to have a way of explaining relatively complex issues in a very simple straight forward manner not requiring one to use a technical dictionary. Although I had what I would call charitably a loose understanding of this issue ,your photo's and great explanation were such that until my mind fails ,I now have locked in, a solid understanding about this issue. There are many who can spew out highly technical jargonease but few who have the kind of understanding that enables them to express complex issues in a simple manner with little sacrifice to clarity and accuracy. I guess I have embarrassed you enough but really you ought to consider publishing some of your stuff.
Respectfully,
Dan :bow:
"Experience is a wonderful thing. It enables you to recognize a mistake when you make it again."

#21 BarrySimon615

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Posted 19 April 2004 - 05:48 PM

The two upper pictures in the collimation photo were taken with the "cheshire" eyepiece in the focuser of a Unitron 60 mm f/15 refractor. The left image shows the scope perfectly collimated, in the right image I purposely took the collimatable objective cell out of collimation (grossly) to get that "overlapping rings" image. Most refractor telescopes would not be this grossly out of adjustment. However any degree of miscollimation is easy to see.

The Miyauchi binocular photo is thru the left barrel only. Stacking left barrel and right barrel images would only confuse the issue. The right barrel did appear to be a bit better. Dymo label tape is used to thicken up the barrel of the Cheshire to match the i.d. of the Miyauchi eyepiece receptacle.

As I said before, a "Cheshire" is a very useful tool. It can and should be used on prospective purchases, testing with a telescope star diagonal removed, and then retested with the star diagonal in the light path. Last year I purchased a store demo Vixen 102 mm f/9.8 achromatic refractor. The objective cell is not collimatable, but in this case that was an advantage because testing with the Cheshire showed that it was spot on perfect! (Cheap star diagonals are big culprits in making an otherwise good telescope look bad because they are not collimated.)

Another culprit with telescopes these days is that focusing tubes, star diagonals and eyepiece barrels are not made to tight tolerances like they were years ago. There is a lot of slop between parts these days! Accordingly tightening an eyepiece or diagonal in a focuser can result in an eyepiece or diagonal being tilted slightly to the side. This throws off collimation, and if it happens to both diagonal and eyepiece, it can really throw it off. Fortunately this is something we don't have to worry about with binoculars.

Barry Simon


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