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Abbe-König prisms and 3D effect. Roofs and 3D effect?

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Old Tuesday 12th March 2019, 16:36   #1
yarrellii
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Abbe-König prisms and 3D effect. Roofs and 3D effect?

Over the last couple of weeks I have been using (in complete awe) a pair of 7x42 Victory FL. Last year I had a pair of 8x32 FL and their performance was good, but they didn’t wow-me away the way the 7x42 do (besides, the ergos of the 8x32 weren't great for me, they just didn't fit my hands).

I am fully aware that between the 8x32 and 7x42 FL's there are many differences such as type of prisms used (SP vs AK), objective diameter, exit pupil diameter, light transmission, FOV and other technicalities that probably escape my understanding, but the thing that really surprised me (besides the brightness) is the three-dimensionality of the image in the 7x42. Ever since I tried a modern porro I’ve been in love with the plasticity and 3D-effect of the image produced by porro binoculars, and I thought that it was impossible to get something closer in roof binoculars. Until now.

A question to those with a deeper technical understanding: is the enhanced 3D effect inherent to Abbe-Köenig prisms? Or does it get augmented in this case by the huge FOV of the 7x42 FL’s and its remarkable light transmission? Are there any other non-porro binocular that might offer such an experience? Are there any SP roofs with a distinctive 3D-effect?

There are things I don’t like about the 7x42 FL, but whenever I look through them the plasticity of the view is such that I just have to pick my jaw from the floor, especially when looking for passerines among the branches, now that they’re frenzy coming and going looking for stuff for their nests.

Out of curiosity, are the 7x42 FL the smallest AK-prism binoculars available? I see that, given that AK prisms are particularly attractive for its light transmission, most of the (small) offer seems to be limited to chunky monsters in the x50/x56 league.

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Old Tuesday 12th March 2019, 17:00   #2
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Regarding size of the 7x42 AK prisms: Have you seen the "cut away" view of the 7x42FL in Allbino's review of the 8x42FL? They are the same size. The 7x42 uses the 8x42 eye piece. The objective tubes are shortened for the 7x42.

https://www.allbinos.com/238-binocul...x42_T*_FL.html

Bob

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Old Tuesday 12th March 2019, 17:09   #3
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Bob, thanks for the input. I have indeed seen that image and another one (I can't remember whether also in Allbinos) where there are three cut-away views showing the evolution (i. e. shortening) of the AK prism binoculars in the Zeiss line-up, from the very long Dialyt to the FLs. But that does not tell me much :( Does the image of the prisms show part of the "3D trick"?

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Old Tuesday 12th March 2019, 17:57   #4
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The 3D impression was probably enhanced by the increased depth of field of the 7x binocular compared to the 8x.
The objective spacing of roof prism binoculars is not always coincident with the eyepiece spacing (IPD). Usually it's a little larger, though IIRC it was somewhat narrower on the now discontiued Nikon HGs. The difference however is so small as to have little effect on 3D perception. A small offset could be achieved with either Schmidt-Pechan or Abbe-König prisms.

John

PS:- The 7x42 Zeiss FL not only required shorter objective tubes than the 8x42, but also shorter focal length objectives.
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Old Tuesday 12th March 2019, 18:27   #5
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FWIW, the Allbinos cutaway in Bob's link is mislabeled as the 7x42 FL. The objective tube is too long for the 7x. It's either the 8x or 10x, both are the same length.

The cutaway below of three 8x56 Zeiss binoculars mentioned by yarellii was also mislabeled by Allbinos. Top is the Dialyt, middle is the Night Owl and bottom is the original Victory, not the Victory FL.

I don't personally sense much difference in stereopsis from the slight offset of the AK prisms, but I do notice a change in subjective magnification at close distances from such slight changes in objective spacing.

Henry
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Old Tuesday 12th March 2019, 20:06   #6
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John, Henry, thanks for the hints and the valuable info.
It is probably the 7x working with my eyes, because I do perceive a certain 3D-ness (for lack of a better term) to the image. This is especially noticeable when looking at branches not far away, and something I don't recall from the 8x32 (I haven't compared them side by side, so my memory could be flawed) or from any roof, for that matter. I have never used a 7x roof, so there could be something... The only 7x I've used have been porros, and all share that plasticity. How much of that is due to the 7x and how much is due to the fact that they are porro... dunno. These are the first AK binoculars I've looked through, so basically I have more doubts than certainties
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Old Wednesday 13th March 2019, 07:43   #7
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I discussed this type of effect with an industry product developer and while we didn't discuss the slight offset caused by AK prisms he attributed the effect partly to a 7x increased depth of field but mostly due to the reduction in magnification which reduces the telephoto compression and makes the view more expansive depth-wise. In several places on the internet you can find pairs of photos that show the same view. One taken with a longer focal length lens (higher mag) and the same view taken with a shorter focal length, wide-angle, lens (lower mag). In the former there appears hardly any distance between objects pictured one behind the other while in the latter you can see that there is plenty of room to walk between these objects.

The reason for my discussion with this guy was because when visiting a coast that I know well from many visits using 8x and 10x binos I was startled when using a 7x to notice that I could easily perceive the distance between a set of interlocking headlands whereas with the higher mag binos these headlands looked crammed closely together.

I find this feature of 7x binos to be very attractive and gives a feel of depth to the view that could easily be described as 3D even though it isn't really.

Lee

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Old Wednesday 13th March 2019, 08:41   #8
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Troubador, thanks this is really interesting. I think I know what you mean (from experience with tele objectives). Very interesting indeed, I had no idea about this happening in binoculars to such extent. Now I'm tempted to get a 7x SP to compare with a 7x porro and 7x AK
Maybe someone who has a 7x AK and a 7x SP at hand can try to do a comparison. Although I'm afraid that differences in other fields/aspects will actually matter more (or have a greater impact on the view) than whether the prisms of any given roof binocular are of one configuration or the other. Just curious.
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Old Wednesday 13th March 2019, 09:01   #9
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Lightbulb

Yarrellii, the confusion between steropsis or the real 3-D effect and depth of field is pretty rampant here on BF. It's persistence is most annoying !
The confusion runs both ways (ie. a real 3D view does nothing to increase the dof). Stereopsis refers to the greater separation of the objectives than the ipd of the eyepieces. This is the only real source of '3D'.

This is further confused with people describing views as '3D' when clearly they are referring to other things. In these instances I prefer to always be specific and use other terms like 'quasi-3D'. The translated from German term 'plasticity' further complicates the issue (I still don't think native English speakers have a precise understanding of that one yet ...).

Factors that give rise to this quasi-3D effect are lesser telephoto compression given by the lower powers, more depth of field given as magnification lowers, field curvature profiles and effects, pincushion distortion levels and profiles, Fov, AFov, and some sort of dark arts voodoo magic related to the Petzval curvature of the eye and image plane specifics (the NoctiVid seems to be the chief exponent so far here) .... eyepiece alignment /distance margin of error and Randpupille also play a part, but that's probably getting overly complicated for these purposes.

All of this is compounded by the users optical physiology, age, neural processing, and the environmental conditions (lighting, viewing distance, topography, subject /background spacing etc) at the time.

Anyone claiming a '3D' view out of roof prisms is likely to be describing a handy confluence of these factors for a bin with them at the time ....

I've noticed a slight 'quasi-3D' like quality to the view with the roof prism Swarovski 10×50 SV. I also note this slight effect in the Zeiss HT 8×42 --- how much of that is due to the slightly greater objective spacing because of the A-K prisms, and how much is due to those other factors I can't say. My Zen-Ray ED3 8×42 has some pretty wild pincushion distortion, and slight field curvature, and a wide Fov which also gives a pretty good 'quasi-3D' effect.

You can go through quite an effective demonstration for yourself by comparing a Porro and an S-P Roof of the same magnification, objective diameter, and Fov. Looking down a creek /riverside is very good for the purposes of this little experiment.

* Pick some rocks /trees etc at the shortest and farthest limits of being in focus either side of a focus position.
* Compare the two bins. Precisely noting the in-focus extremities.
* You will see that the limits are exactly the same.
* This is despite your brain swearing blind that the Porro has greater dof.
* What you are 'seeing' is the 3D Stereopsis effect.
Now you will never again confuse the two

Hope that helps a bit.





Chosun

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Old Wednesday 13th March 2019, 10:40   #10
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Chosun, wow, very informative, thanks. Given my limited knowledge I guess I must plead guilty of the above mentioned sins of confusing terms Really interesting explanation, those are somehow the kind of ideas I was looking for. As you mention I am aware that in porro prism binoculars the distance between the objectives is greater than the IPD, hence my surprise when using the 7x42 FL (roofs) and perceiving that 'quasi-3D' like quality (or 3D-esque?) that I didn't expect to be there, or to manifest in such a way (in Spanish we also use the term 'plasticity' for an image, or a mental/written image). I've only used 7x porros, and they also share this characteristic, but I've never looked through a 7x roof. That's one of the reasons that sparked my curiosity on whether AK prisms could have anything to do.
I'll sure make the experiment you mention. Thanks for taking your time and explaining in such detail and with such patience, this forum is a great place indeed. Thanks for making it what it is.

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Old Wednesday 13th March 2019, 13:25   #11
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Just to clarify: offset is not only to be found on binoculars with A-K prisms. It is often a design neccessity there because most binoculars with A-K prisms have large objectives and a large offset is needed to allow smaller IPDs.

I measured the offset of the following binoculars, all with S-P prisms, at around 65 mm IPD. Objective spacing and IPD were measured by subtracting one barrel diameter from the overall width.

Swarovski CL2 8x30: coaxial (verified at min. and max. IPD)
Kowa Genesis 8x33: +1 mm
Meopta Meostar 7x42: +1 mm
Swarovski SLC 7x42: +2.5 mm
Swarovski EL 10x42 SV: +4.5 mm

John

PS:-The values are differences in objective spacing and IPD, so the horizontal offset is half the above.

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Old Wednesday 13th March 2019, 19:54   #12
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Originally Posted by Chosun Juan View Post
Yarrellii, the confusion between steropsis or the real 3-D effect and depth of field is pretty rampant here on BF. It's persistence is most annoying !

Chosun
When you get folks to stop that, please take a bow; I've been trying for a VERY long time!

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Old Thursday 14th March 2019, 21:12   #13
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All,

Looking at the woman potter do you perceive spatial depth, and do you have a sense of how far the woman is from the wall behind her? What about the distance relationships between objects on the shelf?

Now close one eye. Does spatial depth perception increase, decrease, or remain unchanged?

Are two eyes really necessary to perceive 3D depth?

Ed
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Old Thursday 14th March 2019, 22:30   #14
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All,

Looking at the woman potter do you perceive spatial depth, and do you have a sense of how far the woman is from the wall behind her? What about the distance relationships between objects on the shelf?

Now close one eye. Does spatial depth perception increase, decrease, or remain unchanged?

Are two eyes really necessary to perceive 3D depth?

Ed
Nope, but more information (i.e. two eyes) enhances the 3D perception. A deceased friend born with one functioning eye had no problem determining distances, driving, playing ball, etc. His solution: "I just learned how to do it all through trial and error."

See...
https://www.ncbi.nlm.nih.gov/pubmed/23892232

PS
The NOPE was my reply to Ed's last question.
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Old Thursday 14th March 2019, 23:31   #15
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Question

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Originally Posted by elkcub View Post
All,

Looking at the woman potter do you perceive spatial depth, and do you have a sense of how far the woman is from the wall behind her? What about the distance relationships between objects on the shelf?

Now close one eye. Does spatial depth perception increase, decrease, or remain unchanged?

Are two eyes really necessary to perceive 3D depth?

Ed
Ed, has that picture been enhanced in any way? or is it just a straight photograph? (ie. single lens, or eye, view). Obviously great care has been taken with the lighting. The reason I ask is that street artists, tattooists, etc are doing amazing things with 3D art. It is amazing what our brains construct.

As far as looking at the picture and doing your experiment - I notice no difference - other than my eyes seem to have changed again, and I'm back to being right eye dominant again - which would be fantastic for my bowls, if only I was able to be back playing at the moment ! sigh.



Chosun
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Old Thursday 14th March 2019, 23:50   #16
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ED,

Nice pic...regarding the question, No I do not, but she is quite close to the wall isn't she. Regarding the pottery, shadows and lighting do accentuate the contrast very well.

Andy W.
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Old Friday 15th March 2019, 22:54   #17
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@Piliatus. Thanks for the PubMed link to "Seeing in 3-d with just one eye: stereopsis without binocular vision." Fortunately, the whole APS article can be downloaded from ReserchGate, so I've attached it below. It's well worth reading. However, I'm absolutely stunned that it could be published as recently as 2013, in a refereed psychology journal, with nary a mention of James Gibson and his famous theory of visual gradients. So I've attached that below too. Recent physiological evidence has been found for gradient detectors.

@ Chosun. I just scanned the picture from an 'Art Restoration' book that's been sitting on our coffee table. As far as I know, it's a straight photograph, but as Andy mentioned the lighting is professional. Nonetheless, in general, I get more enjoyment viewing photographs with one eye than two. For me, the objects "pop out" more.

Regarding binoculars, I doubt that the prism type per se has much to do with stereopsis, however, magnification and field of view clearly do. Less of one and more of the other enhances the effect, in addition to retinal offset.

Now go back to the potter picture and cup your hands to eliminate the border. For me, the 3D effect is amazing — using either one eye or two.

Ed
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Old Friday 15th March 2019, 23:55   #18
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@Piliatus. Thanks for the PubMed link to "Seeing in 3-d with just one eye: stereopsis without binocular vision." Fortunately, the whole APS article can be downloaded from ReserchGate, so I've attached it below. It's well worth reading. However, I'm absolutely stunned that it could be published as recently as 2013, in a refereed psychology journal, with nary a mention of James Gibson and his famous theory of visual gradients. So I've attached that below. Recent physiological evidence has been found for gradient detectors.

@ Chosun. I just scanned the picture from an 'Art Restoration' book that's been sitting on our coffee table. As far as I know, it's a straight photograph, but as Andy mentioned the lighting is professional. Nonetheless, in general, I get more enjoyment viewing photographs with one eye rather than two. For me, the objects "pop out" more.

Regarding binoculars, I doubt that the prism type per se has much to do with stereopsis, however, magnification and field of view clearly do. Less of one and more of the other enhances the effect, in addition to retinal offset.

Now go back to the potter picture and cup your hands to eliminate the border. For me, the 3D effect is amazing — using either one eye or two.

Ed
Thanks Ed!
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Old Saturday 16th March 2019, 01:11   #19
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To give an easy entry point for many, see the Wikipedia entry on Depth Perception: https://en.wikipedia.org/wiki/Depth_perception

There is a list and explanation of 15 monocular cues (and 3 binocular ones)

This should in turn make it easier to follow the more scholarly attachments to Ed’s post #17

John
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