3D perception in monocular systems. Really! (1 Viewer)

[looksharp65]

Was a bit unsure whether to put this here or in the Spotting scopes section, but I figured it might create some more buzz here.
I was out with my scope yesterday, and remembered an experiment I wanted to revisit.
Stage: A line of bigger plants about 50 metres away, flatland in between and finally another row of plants.
I focused the closer row of plants and made left-right and up-down head movements while observing the background apparently move relative to the focused plants in the foreground. Plants in the foreground appeared rock-steady with no movement. Then I refocused to the plants in the background, and repeated the procedure. Now the background appeared to be fixed, while the plants in the foreground were moving relative to the background.
This experiment is probably difficult to perform with binoculars, but perhaps not impossible.

I'm no great instrument optician, but the observations suggest parallax within the image field.
The objective forms what is called a real image, which we see magnified with the eyepiece. A real image could also be projected onto a surface like a wall, a silver film or a sensor, but the rendition will not show this type of depth qualities.

It seems the real image is somewhat more like a miniature of the real world, rather than the flat, projected image. And observing the real image through a high quality eyepiece reveals these details of the miniature image. It is probably not as three-dimensional as a hologram, and unlike a hologram, the eye cannot process a real image, it is invisible until projected or watched with a loupe/eyepiece. But it holds three-dimensional cues despite being in a monocular system
Thoughts?

//L

 

[Binastro]

Hi,

The scope has an objective that has a diameter.

Are you using different ends of the objective as you move around?

There is also magnification involved.

At very close distances I think I used to see 3D with one eye.
But my eyes are not good enough now.

Another thing is that the eye has chromatic aberration and I frequently see different colours in an image in 3D even on a flat screen.

If a scope has chromatic aberration or er even the eye using the scope then I think 3D would appear, particularly at the borders of two colours.

Ed has a different psychological approach to 3D, I think via Gibson's theories.

Regards,
B.

 

[PeterPS]

L & B:
You both have touched upon an interesting related question: can people with monovision see in 3D? Yes they can. For people with binocular vision the brain uses the difference between the two images to provide depth perception information. People with monocular vision use other cues to interpret depth and form a 3D image such as: closer objects are larger, brighter, and have more contrast; also with any head movement you will see changes in the image as near objects move in front of objects that are behind them; and of course memory/experience.

 

[looksharp65]

David, there is this parallax inside the width and height of the real image. Moving the head makes the background move if focus is set to the closer distance. I am not certain it's the peripheral parts of the objective lens that are involved, but head movements require an oblique viewing angle. The effect is quite obvious and chromatic aberration is not involved in the phenomenon.

Peter, you're right about the ways one-eyed individuals can substitute the lack of stereoscopic vision. It is the second last phrase that applies to this phenomenon: '

also with any head movement you will see changes in the image as near objects move in front of objects that are behind them;

Sure, this is not very useful for binoculars since the wiggle room is nearly nonexistent, but for spotting scopes it adds a dimension that's largely unknown. First time I observed this was when watching a Gyrfalcon perching on a fence pole and in the far background were houses and stuff.

This isn't really revolutionary, but the fact that the real image as viewed with the eyepiece indeed posseses three-dimensional qualities is intriguing.
The real image, when projected onto a sensor and watched on a screen, loses this quality. I believe that the inherent 3D quality of the real image adds to the perceived quality even without moving the head around. Obviously, the stereoscopic view of binoculars contribute to the lion's share of depth perception.
Altogether, I find this an interesting phenomenon and also that it's largely overlooked and virtually unknown.

//L

 

[tenex]

What you're doing here sounds equivalent to the use of a shift lens on a camera, which displaces the lens axis from the center of the sensor. This changes the apparent perspective of the view, often to correct converging lines at some distance, but it can also change the relative position of more nearby objects, which is sometimes also useful. I doubt that it's necessary to speculate about intrinsic properties of the "real image" to explain this.

In photography the result doesn't vary depending on the focal distance, but in this case you're shifting one part of the lens system relative to the other, while your eye lens remains centered on your retina.

 

[looksharp65]

What you're doing here sounds equivalent to the use of a shift lens on a camera, which displaces the lens axis from the center of the sensor. This changes the apparent perspective of the view, often to correct converging lines at some distance, but it can also change the relative position of more nearby objects, which is sometimes also useful. I doubt that it's necessary to speculate about intrinsic properties of the "real image" to explain this.

In photography the result doesn't vary depending on where the focal plane is, but in this case you're shifting one part of the lens system relative to the other, while your eye lens remains centered on your retina.

Yes, a tilt&shift lens can, for example, be used for taking photos straight in front of a mirror while keeping the camera outside of the reflected image. It's certainly possible than you're on the right track.

Your use of quotation marks is somewhat disturbing, though. A real image is a well-known optical concept, and it has a distribution in all three dimensions.
It is not a single point, neither is it a two-dimensional virtual representation. Only when projected onto a surface it becomes entirely two-dimensional.
So, while invisible until viewed either with an eyepiece or projected, it is an existing phenomenon in all three spatial dimensions. That is not a speculation.
Real image - Wikipedia

//L

 

[tenex]

It's certainly possible than you're on the right track.

It's a good deal more than possible; only the odd focal effect hasn't been fully worked out, shift within a lens system being unusual.

Regarding 'the "real image"', what I meant was that rather than observing mysterious qualities of the real image, you're simply creating shift effects. Sometimes a quote is just a quote...

 

[elkcub]

L & B:
You both have touched upon an interesting related question: can people with monovision see in 3D? Yes they can. For people with binocular vision the brain uses the difference between the two images to provide depth perception information. People with monocular vision use other cues to interpret depth and form a 3D image such as: closer objects are larger, brighter, and have more contrast; also with any head movement you will see changes in the image as near objects move in front of objects that are behind them; and of course memory/experience.

Peter et. al,

It would be worthwhile to read this article by James J. Gibson. Among other observations, he explains the visual performance of Wiley Post, who was the first pilot to circumnavigate the earth solo. He was also one-eyed.

When viewing photographs I usually find it more 3-dimensional to view monocularly, as, for example, this image of Wally Post.

It's still a matter of debate as to how necessary stereopsis is for 3D perception.
Ed

 

[looksharp65]

It's a good deal more than possible; only the odd focal effect hasn't been fully worked out, shift within a lens system being unusual.

Regarding 'the "real image"', what I meant was that rather than observing mysterious qualities of the real image, you're simply creating shift effects. Sometimes a quote is just a quote...

I don't understand why you impute the word 'mysterious' to me. I'd have guessed your optical knowledge was deeper.
A real image is invisible, but that does not make it any more mysterious than any other optical concept. It is formed by all the focus points the objective delivers, and these appear in a cluster in three dimensions, like a cloud. My naïve interpretation is that the eyepiece works essentially as a loupe when youre watching a real object. Shifting the eye's position away from the optical axis changes the perspective somewhat, and this reveals the three-dimensionality of the object. The shifted position of the eye creates a parallax, but not quite in the ordinary sense, since there's no simultaneous perception of the two positions, as in binoculars.
So, when using a telescope, it's the real image we're watching. No true stereoscopic vision is possible, but the parallax resulting from the shift reveals there's three-dimensional qualities inside it, and that is logical due to its own distribution in three dimension. Nothing strange. This does not contradict your correct explanation that we're dealing with shift effects.

Edit: There is one significant flaw of the real images' three-dimensionality that sets it apart from real objects, and this is obviously that rays from behind an object are blocked by the object itself. It's nothing like a hologram. Just wanted to make it clear that I, too, just like everybody here, understand this.
So the shift effect means that objects in the background, obscured by a more nearby object, can escape from the hidden position by shifting the position of the eye inside the afocal image leaving the telescope.

//L

 

[elkcub]

For those into stereo photography, one way to get the left/right images is by using the "cha-cha" method. I suspect what looksharp65 has found is that the brain can itself put together memory traces from successive views and thereby generate a semistereo effect. (That's an alternate hypothesis. )
Ed

 

[Binastro]

I got great stereo photos flying from La Palma to Tenerife.

As the aircraft flew, the baseline changed and the mountains came out well in stereo.

Brian May, the guitarist and Dr. of Astronomy is involved with stereo.

Regards,
B.

 

[elkcub]

Hey Guys,

The technical description of how a telescope works is attached from Jenkins and White's "Fundamentals of Optics."

There is a real and inverted image formed by the objective that is magnified by the eyepiece and seen as a virtual image.

Be kind.
Ed

 

[looksharp65]

A telescope is an afocal instrument consisting of two focal parts, the objective and the eyepiece. Either can be used to focus the light to their respective focal points.
Took my little William Optics SWAN 15 mm and used it as a very strong loupe. Like any magnifier, it can also be used as a burning glass.
If telescopes were essentially loupes, our eyes wouldn't be able to see the resulting real image because parallel rays from infinity converge to a real image in the focal point.
But the rays exiting the eyepiece are parallel, not converging. Anyone trying to use a telescope or binocular as a burning glass will fail, which clearly proves it is not a loupe. Parallel rays in - parallel rays out says it's afocal.
A loupe refracts the strongly diverging rays from a very nearby object in the lens's front focal point to parallel rays that our eyes, in turn, can refract to the retina.
I believe any further explanation would be superfluous, although my phrasing and details could be improved.

//L

 

[elkcub]

I got great stereo photos flying from La Palma to Tenerife.

As the aircraft flew, the baseline changed and the mountains came out well in stereo.

Brian May, the guitarist and Dr. of Astronomy is involved with stereo.

Regards,
B.

It would be great if cell phone cameras had a "Cha-Cha" mode to allow stereo pairs to be shot and subsequently viewed/printed for stereo (or maybe they have and I'm just behind the times.)
Ed