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Porro extra "3D" view (1 Viewer)

N

normjackson

Well-known member
Just noticed this put forward as a selling point in the Opticron USA brochure for the Savanna porros. I understand at very close distances the extra distance between the objectives in a traditional porro can be a nuisance while at great distances it presumably ceases to be a factor at all.
For viewing something in thicket I guess at moderate distances the separation of the viewpoints for the two eyes reduces the liklihood of the same branch or twig obstructing the item of interest, which is handy.
As for the nicety of an enhanced 3D view, has anyone identified the circumstances where this effect is most noticeable and where it effectively ceases to be significant?
B :)

PS. Just did a quick AB at about 3 metres. Was trying to remember the sense of 3D through the porros and when swap to roof completely thrown by the (false) sense of greater magnification. Tricky.
 
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I find the depth perception thing tricky to understand. My little 7x26 reverse porros give excellent spacial positioning at close range but I suspect that is due to some trick of the field curvature. The big 12x porros I've reported on still give a better perspective than my roofs several hundred yards out where I guess the advantage should have diminished.

David
 
Depth perception and spacial awareness in general seems to vary greatly between individuals (certainly amongst my relatives) - with or without binoculars.
I sometimes wonder whether our lack of need to spear a fish in recent centuries is leading to this being evolved out of town dwelling homo sapiens?
I don't have a problem with porros at close range, but my spacial awareness with binoculars is more to a lack of accomodation in my eyes than with binocular vision in thickets. i.e. I need to adjust focus far more then when younger and judge distance better that way.
I do find porros far more relaxing to look through when scanning in open countryside where, in theory, the 3D effect is minimal!
For real close up work I do find Papilios much better for getting a feel for the shape of a specimin than a similar monocular style device.
So I guess it may boil down to a lack of standardisation between humans.
 
Thanks gentlemen for responding. Yep some of your findings are not completely intuitive and I guess there are a brain punishing number of variables involved in answering the question I seem to be trying to ask.

I've been trying find a view which shows the traditional porro's "3Dness" to best advantage.
Best I've come up with so far (after minutes of relaxing research in a deckchair) is viewing subject in attached photo (tangled stems and flowers a foot or so in depth) at 25 feet. I used a 7x roof in which the objectives spacing is about half of the 7x50 porro (would be much greater difference with David's 7x26 reverse porro I guess). Indeed I think I do perceive some difference but don't think I've completely sold myself yet. Of course, J, I may be just insensitive having never speared a fish : didn't those illustrations in the physics book at school illustrating refraction just make it look too difficult. And as for those archerfish...
 

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normjackson said:
Just noticed this put forward as a selling point in the Opticron USA brochure for the Savanna porros. I understand at very close distances the extra distance between the objectives in a traditional porro can be a nuisance while at great distances it presumably ceases to be a factor at all.
For viewing something in thicket I guess at moderate distances the separation of the viewpoints for the two eyes reduces the liklihood of the same branch or twig obstructing the item of interest, which is handy.
As for the nicety of an enhanced 3D view, has anyone identified the circumstances where this effect is most noticeable and where it effectively ceases to be significant?
B :)

PS. Just did a quick AB at about 3 metres. Was trying to remember the sense of 3D through the porros and when swap to roof completely thrown by the (false) sense of greater magnification. Tricky.
Click to expand...

Norm,

It's simply very complicated, but, then, so is your question. ;)

Stereopsis involves the brain merging monocular and binocular visual cues, as well as oculomotor feedback information, to create a three-dimensional "view" (i.e., a perceptual space) that maintains valid inter-object distance relationships. It is of no particular significance for astronomical observation, not only because of the great distances involved, but because there are no intervening objects.

For terrestrial observation, objects generally occupy the scene from near to far and stereopsis allows us to appreciate relaive distance relationships in the whole scene. The ability to do this is referred to as a stereo-acuity and has been studied extensively. However, I am not aware of stero-acuity being measured with magnifying binoculars. This would no doubt involve more than simply applying the mathematics of retinal image disparity (which isn't simple), since the normal oculomotor relationships of accommodation and convergence are affected, and even the widest spaced Porro isn't scaled proportional to magnification. (Note that the problem with Porros at close distances is that the eyes can't converge properly. The Papillio overcomes that problem by using optical convergence.)

In general, however, since no one is able to walk around while looking through binoculars, the advantage of stereopsis is obviously not so much to aid physical navigation through real space, but to aid mental navigation through virtual space. The more of it the better, I say, but how much better is traded off with the other features that distinguish Porros from roofs.

Ed
 
Norm,
I have been reading the Optical Society of America Handbook vol. III on Vision, and I can at least recite the textbook answer.

A view is perceived as "stereo" right to the limit of visual acuity which is about 1 arcmin for 20/20 vision. That is, as long as the direction of view of an object in your two eyes differs by at least 1 arcmin, you will see a "3-d effect". (That is awesome, as are many things about eyesight according to this book, which I greatly recommend to seeing buffs.) I'd take this value with a grain of salt, but it is useful to work out some numbers.

If your eyes are 60mm apart, for naked eye that distance would be 206m.
In a roof binocular with that same optic separation, the distance can be scaled by the magnification: Roof binocular, 2060m at 10x.

With a Porro, the separation about doubles to 120mm, and the distance can be scaled again by that: Porro binocular, 4120m at 10x.

I can't decide if I really like enhanced 3-D or not, but it's an unpleasant shock swapping back and forth.
Ron

PS I just saw Ed's post and he makes an interesting point about the near response, but does this really complicate matters? Yes, there is a near response connecting convergence, focus range, and pupil opening. But you simply must point your eyes together at the image to see it, and, will presumably set the focus comfortably in accord with your own near response, for the magnified convergence angle. Do you think that is over-presuming of me, Ed?
 
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It is probably just me, but i have such great difficulty getting the 'enhanced 3 D effect' that I doubt it exists.

There was a Japanese designed binocular with objectives at the end of 6" long optical extensions, so they acted as miniature range finders. Those might perhaps have produced a perceptible stereo image.
However, reports of the East German OEM-2, a 14x glass with a 51 cm baseline said that only about a third of the recruits were able to detect the distance marker well enough to use the device. That suggests stereoscopic vision is not universal.
 
A factor affecting the greatest distance at which stereo could be perceived in a binocular would be the precision of collimation. Apparent collimation errors of 10 or more arcmin are common, and considered acceptable. That would seem to blow my simple calculations right out of the water.
Ron
 
Not everybody has top-range stereoscopic vision. Some will never reach it, either.
Make sure not to confuse depth of field/depth of focus with 3D-perception.
The former is a quality that does not require double barrels, the latter is a quality that almost exclusively needs the image disparity arising from the physical distance between the two barrels.
(I say almost exclusively, because I've discovered that when looking at a bird through a scope at decent distance, the far situated background will seem to change its position relative to the bird if the observer moves his head sidewise)

Here are some findings on the subject, strangely buried in a binocular models thread.
Later on in the thread I've made some corrections where my assumptions have proved incorrect.

http://www.birdforum.net/showthread.php?t=173492&page=2
 
ronh said:
Norm,
I have been reading the Optical Society of America Handbook vol. III on Vision, and I can at least recite the textbook answer.

A view is perceived as "stereo" right to the limit of visual acuity which is about 1 arcmin for 20/20 vision. That is, as long as the direction of view of an object in your two eyes differs by at least 1 arcmin, you will see a "3-d effect". (That is awesome, as are many things about eyesight according to this book, which I greatly recommend to seeing buffs.) I'd take this value with a grain of salt, but it is useful to work out some numbers.

If your eyes are 60mm apart, for naked eye that distance would be 206m.
In a roof binocular with that same optic separation, the distance can be scaled by the magnification: Roof binocular, 2060m at 10x.

With a Porro, the separation about doubles to 120mm, and the distance can be scaled again by that: Porro binocular, 4120m at 10x.

I can't decide if I really like enhanced 3-D or not, but it's an unpleasant shock swapping back and forth.
Ron

PS I just saw Ed's post and he makes an interesting point about the near response, but does this really complicate matters? Yes, there is a near response connecting convergence, focus range, and pupil opening. But you simply must point your eyes together at the image to see it, and, will presumably set the focus comfortably in accord with your own near response, for the magnified convergence angle. Do you think that is over-presuming of me, Ed?
Click to expand...

Hi Ron,

Good find. :t:

Nothing like a few facts to perk up one's interest. Frankly, I'll have to get a copy myself, and also think about your scaling conclusions. Is there any indication in the book that the statement about stereo perception and acuity generalizes to the domain of "aided acuity," i.e., magnified images? On the surface it seems reasonable.

Regarding near working distances, one issue is that converging the eyes with conventional binoculars does not alter the field overlap as with normal vision. Also magnification increases with closer working distances and, except for the Papillio, the views must be markedly cross-axis.

Ed
 
ronh said:
A factor affecting the greatest distance at which stereo could be perceived in a binocular would be the precision of collimation. Apparent collimation errors of 10 or more arcmin are common, and considered acceptable. That would seem to blow my simple calculations right out of the water.
Ron
Click to expand...

Well, you need not be that hard on yourself. It's one thing to talk about what could be achieved theoretically, and quite another to talk about what has been achieved in practice. I would propose that collimation error may have a lot to do with differences in perceive stereopsis, and, hence, something to do with the quality of the optics. No?

Ed
 
looksharp65 said:
Not everybody has top-range stereoscopic vision. Some will never reach it, either.
Make sure not to confuse depth of field/depth of focus with 3D-perception.
The former is a quality that does not require double barrels, the latter is a quality that almost exclusively needs the image disparity arising from the physical distance between the two barrels.
(I say almost exclusively, because I've discovered that when looking at a bird through a scope at decent distance, the far situated background will seem to change its position relative to the bird if the observer moves his head sidewise)

Here are some findings on the subject, strangely buried in a binocular models thread.
Later on in the thread I've made some corrections where my assumptions have proved incorrect.

http://www.birdforum.net/showthread.php?t=173492&page=2
Click to expand...

I missed this thread entirely. Thanks for finding it again.

Ed
 
ronh said:
Ed,
No, the Handbook doesn't mention the issue of stereo perception in presence of magnification.
Click to expand...

Ron,

I downloaded this lecture to my technical file some time ago, and it may still be available on the Internet. See pgs. 6-7 for an expanded discussion of the relevant equations with no magnification. If the Handbook isn't at least this specific, I'll let it go.

A general appreciation of the 'visual horopter' is needed to follow this development, but that's not hard at a conceptual level. http://en.wikipedia.org/wiki/Horopter

Ed
 

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Ed,
I think you would enjoy the Handbook. It lacks some of the look of mathematics, but still contains the essentials. It probably goes even deeper into the fundamental concepts. And I think you would be impressed, that it is such a broad range of up to date knowledge in a single book.

Thanks much, however for the reference to the enjoyable lecture. Its little definition of the horopter is clearer to me than the long winded stuff I could find.

A repeat reading reveals the Handbook's ballpark minimum disparity giving steropsis is smaller than the 1arcmin I originally stated, rather 20-40 arcsec. It is curious that, near the end, the lecture gives a smaller angular disparity than the handbook for what can be perceived steroptically: 2-10 arcsec! This is about what the handbook calls the limit of "hyperacuity" or vernier acuity, which exceeds the simple "resolution" of the retina, presumably though the eye's ability to analyze diffraction patterns on the retina. That is far out, I think. Either result, 20-40 arcsec or 2-10 acsec, requires hyperacuity, which gets an interesting passage all its own.

By my simplistic method, 2arcsec instead of 1arcmin would extend all the distances in my earlier post by a factor of 30! Too bad it all goes straight to hell from collimation errors in the best binocular ever made.

The same repeat reading reveals, deep in the book, a treatment of stereo view under magnification! Sorry I overlooked that before, have not read it yet.

Anyhow, up close, a Porro really makes your eyes cross, huh. That much, I can understand!

On topic but off the horopter,
Ron
 
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There'a a new edition available. Vol. III came out in 2010. Thanks, Ron for advise. I will take a look at it in the library.

Steve
 
Must thank the further contributors to the thread. Good to see that the claim about "the superior 3D views" in porros is at least not unchallenged (after all, that wouldn't be healthy would it?) And hopefully the more "techy" stuff here will refine understanding once absorbed; I shall continue re-reading |=)|
Looksharp65's comments on the thread he provides a link to go some way to answering the question I was going to pose when it became apparent the first was too general : how could a dealer, say, go about providing a demo which had the best chance of illustratrating this feature of traditional porros.
Maybe as an aid someone could design something like the periscope binocular here with swivelling objectives |:D|
B :)
 

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