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Elliptical sharpness range of wide-angle binoculars

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#1 cnuser

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Posted 22 November 2020 - 11:18 AM

Hello friends of the night!

 

I currently own 2 wide angle binoculars with apparent field of view (AFoV) of about 60 degrees (according to ISO 14132-1:2002) or about 66 degrees using the simple formula (TFoV x magnification).

 

When I look to the edge of the field of view, the sharp area is elliptical (lying ellipse). I see the elliptical sharpness with normal alignment of binoculars - like every person hand holds binoculars. If I turn the binoculars by 90 degrees and look through 1 tube with one eye, I see the sharp area of the field of view circular. This effect occurs with both binoculars, both tubes and both eyes. I therefore exclude eye problems and errors of the binoculars and assume that this is due to the imperfect alignment of the binoculars with eye at a pupil position that deviates more from the optical axis (view to the edge with wide angle binoculars). When looking into binoculars rotated by 90 degrees, you unconsciously align optical axis from the used tube probably better to the pupil with view to the edge - at least differently to normal viewing with 2 tubes to edges/rim. Sorry, english language isn't my native language.

 

Does this effect also occur with you? Which AFoV has binoculars? Is there a better explanation than I suspect? Is there a technical term for "lying ellipse sharpness area"?

 

CS and best regards.


Edited by cnuser, 22 November 2020 - 11:52 AM.


#2 FLT-Astro

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Posted 22 November 2020 - 12:00 PM

Your English is clear and concise, my compliments, my German is horrible. I'll check this with my Oberwerks 10 x 50 ultras today and tonight as I find this concept very interesting.

 

I do have a question? Is this even noticeable in the day or more in the night or both?

 

Just for fun I went to Google translate to convert the above into German

Ihr Englisch ist klar und prägnant, meine Komplimente, mein Deutsch ist schrecklich. Ich werde dies heute und heute Abend mit meinem Oberwerks 10 x 50 Ultras überprüfen, da ich dieses Konzept sehr interessant finde.

Ich habe eine frage Ist das überhaupt am Tag oder mehr in der Nacht oder in beiden spürbar?

Nur zum Spaß ging ich zu Google Übersetzer, um das oben Genannte ins Deutsche umzuwandeln

 

 (don't want to get too far off topic.) ; )



#3 cnuser

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Posted 22 November 2020 - 01:23 PM

I observe the night sky with small binoculars (Nikon Monarch HG 8x42, Hawke Frontier APO 10x42) without tripod, with trembling, with shaking. Therefore I prefer to evaluate edge sharpness during the day with horizontal sight using the following test: I look for a small object at a distance of about 30 m / 33 yds whose details the binoculars just barely resolve, e.g. significant cones on trees or meanwhile dried last flowers of roses. Then I swivel the binoculars slightly so that the flower or cone appears at the edge of the field of view. I memorize the place or area of the field of view where petals or the scales of the cone can not be distinguished anymore or at least worse. This is for me the best separation of sharp and unsharp area of FoV without tripod (I don't own), hand hold. So I see a greater sharp area left and right, the sharp area is for my two eyes a lying ellipse.

 

Thanks for your planned test with Oberwerk bins. I think, with tripod you can also use stars for testing.

 

For FLT-Astro with Google- or DeepL-translator (DeepL is imho better):

Danke für die 1. Antwort auf meinen 1. Beitrag im Forum. Über dein Kompliment habe ich mich sehr gefreut. :-)


Edited by cnuser, 22 November 2020 - 02:01 PM.


#4 FLT-Astro

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Posted 22 November 2020 - 07:37 PM

Hi cnuser. I tested my Oberwerks 10 x 50 Binos and here's what I discovered.

 

I used a 1/3 moon shining brightly at about a 45* angle in my southern sky. I centered the moon on a tripod and moved the binoculars up and down, then left and right. The binoculars were very steady and stable on the tripod. I tried both eyes in each of the tubes to confirm what was very obvious to me. With the binoculars in a normal handheld position (OO), I'm pretty sure I reconfirmed your findings. I drew a simplified diagram of the primary usable field of view, which I estimate to be 70% horizontal or left and right and about 60% vertical. Basically the same as your test, but I did not spin the Binos. The usable field of view was not the same in each tube, so my drawing is generic, but it illustrates what I've found. The clarity seemed much better at the edges in the daytime, but I will recheck that tomorrow in the daylight.

 

https://www.cloudyni...22-at-62152-pm/


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#5 cnuser

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Posted 23 November 2020 - 01:42 AM

Hello FLT-Astro,

thanks for the test, your nightly observation is exactly what I noticed during the day. What do you observe with 1 eye, with 1 tube, the binoculars turned by 90 degrees?  Even a circular sharp area? Don't let strangers see you so, they think you are a big unicorn.  :-)

As a supplement:
I observe without eye glasses / spectacles, without contact lenses. And you? I only noticed the described effect with wide-angle binoculars with little edge blur, with modern roofs. Not with classic wide-angle binoculars, old porros with 1/3 edge blur or more. At least I don't remember anymore, I don't have porros at the moment, can't evaluate porros.
Have fun experimenting!


Edited by cnuser, 23 November 2020 - 01:57 AM.


#6 FLT-Astro

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Posted 23 November 2020 - 05:48 AM

When using binoculars, I prefer viewing in wide-angle, with both eyes, for sweeping and searching the sky. Except for reading glasses, I'm lucky that I do not need any eyewear. I mostly mount my binoculars on a tripod with a fluid head. Sometimes I use a rubber ball (about 25+-cm) filled with dried beans as a method to steady the Binoculars against trees or against the ski-rack or the top of my 4-Runner. I shake and wiggle a lot so I always use some type of support to stabilize the view.

 

This winter, I plan on completing a few lists with Binos. I've just purchased a "like new" pair of 15 x 70s from cloudy nights classifieds, so the extra magnification might be useful. I enjoy the wider field of view in both binoculars and in telescopes. I'll try to stay with the 10x50's if possible.

 

I really thought more would join in this conversation.  :  )


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#7 cnuser

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Posted 23 November 2020 - 01:28 PM

 I'm lucky that I do not need any eyewear. 

..

I really thought more would join in this conversation.  :  )

There we have one thing in common: I also only have reading glasses. Obviously, we both have healthy eyes, which is probably not what makes the sharp field elliptical. In order to exclude eye defects and defects in the used glasses, I ask you to do please a similar test as described in posts #1 and #3 (in daytime, bins upright / on edge, only 1 tube, 1 eye). If you see a circular sharp field, it is not due to the eyes or the binoculars. But if the ellipse is upright, it is due to the binoculars. With a circular sharp field as result I am not the only one who sees the effect.

 

By the way, I observe the stars with light 42er bins lying in a deck chair, I have a garden. But I find your stabilization method with the rubber ball filled with dried beans interesting, extraordinary.

 

Yes it is a pity that not more people participate in the thread, report experiences. But what you reported already gives me confirmation. Thanks for your time.


Edited by cnuser, 23 November 2020 - 01:33 PM.


#8 FLT-Astro

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Posted 23 November 2020 - 04:19 PM

Confirmed in the daytime with your test of a 30m small object and rotating the Binos. The clear in-focus area is about the same as in the picture that I drew in a prior post.   One other note is that when the object is near the edge of the FOV I am able to adjust the focus-knob and bring the object into focus, but of course the center of FOV becomes out of focus.  So the true in-focus center field of view is about, 60-65% vertical and 70-80% horizontal.

 

Clear skies to you.



#9 Henry Link

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Posted 23 November 2020 - 08:26 PM

This phenomenon has come up a number of times at Birdforum. Here's the most recent thread:  https://www.birdforu...ut-axis.393234/

 

Increased sharpness on the horizontal axis comes up in the last paragraph of post #6.


Edited by Henry Link, 23 November 2020 - 08:30 PM.


#10 FLT-Astro

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Posted 24 November 2020 - 03:55 AM

Hi Henry. I read through the entire post from BirdForums. I'm not sure if the phenomena described in those posts accurately describes this phenomenon. I say this because I'm not stationary when looking through the eyepiece to see the edge blur. I'm not viewing an object with binocular vision (both eyes) and then looking left and right or up and down to see the edge blur. I'm moving both eyes and/or a single eye all over the place...and through both or a single tube and to the side or the edge of the eyepiece exit pupil and from lots of different angles, basically all over the eyepiece exit pupil. I can still clearly see when the focus begins to blur near the edges from many different angles. In other words, the edge blur can be seen when viewing from any angle or distance through the eyepiece, and it's visible through monocular as well as binocular vision. I did read that the blur is less noticeable with dark-adapted eyes but haven't tested that yet. Maybe tonight.


Edited by FLT-Astro, 24 November 2020 - 03:56 AM.


#11 cnuser

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Posted 24 November 2020 - 07:30 AM

Confirmed in the daytime with your test of a 30m small object and rotating the Binos. The clear in-focus area is about the same as in the picture that I drew in a prior post.   One other note is that when the object is near the edge of the FOV I am able to adjust the focus-knob and bring the object into focus, but of course the center of FOV becomes out of focus.  So the true in-focus center field of view is about, 60-65% vertical and 70-80% horizontal.

 

Clear skies to you.

Hello, the "error" or better the phenomenon does not wander.  What remained constant? Your eyes, your physiognomy. The optics of bins is imho to exclude. Our observations differ here, in my case the lying ellipse of the sharp field changes to a circle when the binoculars are rotated by 90 degrees (observation of the same effect with 2 binoculars). Do you have any other small (handheld) binoculars to test? CS



#12 cnuser

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Posted 24 November 2020 - 08:02 AM

This phenomenon has come up a number of times at Birdforum. Here's the most recent thread:  https://www.birdforu...ut-axis.393234/

 

Increased sharpness on the horizontal axis comes up in the last paragraph of post #6.

Hello Henry,

I have read the thread a few weeks before. Before I post, I first use search engines with conclusion to this thread:

We need a scientific, anatomical-medical explanation (document) for 2 human eye rotation points or a displacement oft the rotation point during horizontal versus vertical rotation, as I suspect. This would easily explain the effect I described and the effect found in the BF (different kidney beans horizontal vs vertical). 

A simple technical paper from zeiss in german language but with pictures: https://www.zeiss.de...ndrehpunkt.html

This website in english I see without pictures: https://www.zeiss.co...-rotation-.html

My theory: The center of rotation of a non-spherical eye (nearsighted or farsighted, eye is an ellipsoid) could shift due to counter pressure from the eye sockets - different for horizontal and vertical rotation. But I'm not near- or farsighted. Only a little farsighted with reading glasses 1 dpt because age, eye lens with too little accomodation. Are my eyes nevertheless ellipsoids, non-sperical?

 

According the link to birdforum:

" ... BTW, this phenomenon first came up in a different discussion. People occasionally report better edge sharpness near the field edge of the the horizontal axis compared to the vertical axis. Most of the time that's not a binocular defect. It's caused by the very same difference in vertical and horizontal vignetting described above. The extra sharpness at 9:00 and 3:00 occurs when the vignetted exit pupil becomes so much smaller than the eye's pupil that it acts like a camera lens diaphragm went stopped down to a small aperture to create wide depth of field. In a binocular the effect is to bring objects near the field edge, normally unfocused by field curvature, within the enhanced DOF just before they are completely blocked from view by the vignetting.

Henry"

I'm not agree with this theory, because the tubes of binoculars are rotationally symmetric and therefore the vignetting should be the same on the entire edge of the image field. Minor errors of the alignment of the individual optical elements (lenses, baffles) with respect to the optical axis e.g. during collimation are probably negligible. (Mechanical parts for moving lenses must not cause vignetting, prisms only a little in light, small bins.)

Conclusion:

Rotationally symmetric vignetting in a single tube, this is according to my observations. Almost the same "cat eyes" (equal shaped) of the exit pupils on the edges of oculars during oblique view (tilting of the binoculars in different directions against window or so).

CS, thanks for reading and best regards

 

(If my texts seem hard or bossy: Sorry, english language isn't my mother tongue, not my native language.)


Edited by cnuser, 24 November 2020 - 03:27 PM.


#13 FLT-Astro

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Posted 24 November 2020 - 03:59 PM

The edge blur is visible without eye rotation. Simply move your head around, keeping your eyes straight ahead and look for the edge blur from different angles. I tried to convey that in my last post, but anyhow, this discussion truly doesn't further my astronomy pursuits. It does delve deep into anatomical functions of the eye and possibly binocular design limitations or shortcomings, but no matter. I'm out.  Clear skies.



#14 KennyJ

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Posted 24 November 2020 - 04:33 PM

Was this thread ever supposed to be about "astronomy pursuits"?



#15 FLT-Astro

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Posted 24 November 2020 - 07:37 PM

And how does your remark contribute in any way to this thread?


Edited by FLT-Astro, 24 November 2020 - 07:53 PM.


#16 KennyJ

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Posted 25 November 2020 - 01:36 AM

< "And how does your remark contribute in any way to this thread"? >

 

If nothing else, it appears to have prevented you from "passing through the exit door", which would be a good thing, because your previous contributions to the thread were as relevant to the OPs' query and as interesting as anyone else's.

 

Your declaration "I'm out" appeared inexplicably sudden and sharp from where I'm sitting, with the reason provided perhaps even more so!

 

Kenny



#17 cnuser

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Posted 25 November 2020 - 01:51 AM

No dispute off topic please.
Many (hobby) astronomers prefer needle- or point-shaped stars in the widest possible field of view. If this is not the case they investigate causes. In the simplest way they buy better and therefore more expensive observation instruments. Or they investigate causes and improve the observation with the existing technology, if necessary with adequate eye glasses, stabilizations etc. Some only improve the eyecups of their binoculars to suit their individual physiognomy. Reasons and improvements could be interesting for silent readers ;-)

Thank you for your understanding.
@FLT-Astro: Many thanks for your time with me.


Edited by cnuser, 25 November 2020 - 02:07 AM.



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