Why The Rift Works (Light Ray Model)

[Randomoneh]

I'm asking why accommodation is needed if light is coming at the same angle - apparent size of the two objects (coin and the Moon) is the same (expressed in arc-degress). Forget about the convergence for a minute, I'm asking about accommodation.

[Fredz]

I'm asking why accommodation is needed if light is coming at the same angle

Accommodation is different when you look at an object at infinity (the moon) and an object at a close distance (a coin in your hand). You feel the difference because your ciliary muscles don't make the same effort for the two viewing distances, and the brain interprets this as distance information.

apparent size of the two objects (coin and the Moon) is the same (expressed in arc-degress). Forget about the convergence for a minute, I'm asking about accommodation.

There are many other cues that the brain uses to evaluate the viewing distance for these two objects, even only in monocular mode.

If you stand still while looking at them there is always a little bit of uncontrolled movement, the motion parallax produced by this gives another cue about distance.

Also the shape, color and texture of the moon are well known by the brain, he can infer a distance from this, same thing for the coin. If the distant object was visually identical to a coin and the closest object visually identical to the moon it would be harder for the brain to estimate correct distances and it could create a conflict.

There is also some blur than will appear on objects around the coin (the hand for example), this gives an idea about the distance. That will not happen with objects "close" to the moon like clouds, stars, etc.

One funny experience I like to do when I'm lying in the dark before sleep is to close one eye and try to stay extremely still. In these conditions there are times where I'm not able to tell the relative distance from objects, probably because most of the visual cues are not available.

[Randomoneh]

If the distant object was visually identical to a coin and the closest object visually identical to the moon it would be harder for the brain to estimate correct distances and it could create a conflict.

That's the thing - I don't think it would! Even if you trick the eye eliminating all the clues, you still won't be able to focus at "fake Moon" an inch from your eyeball - even if it was a perfect representation and your eye is perfectly still. There is an explanation for this in physics - behavior of the photons and the way lens of the eye bends those photons. Still can't figure it out though.

[android78]

That's the thing - I don't think it would! Even if you trick the eye eliminating all the clues, you still won't be able to focus at "fake Moon" an inch from your eyeball - even if it was a perfect representation and your eye is perfectly still. There is an explanation for this in physics - behavior of the photons and the way lens of the eye bends those photons. Still can't figure it out though.

I disagree. IF the rift does actually make your eye focus at close to infinity (accommodation), then any object that has the separation to make your eyes diverge to almost parallel, then the two will match up and your accommodation reflex will appropriately make you naturally focus at the correct depth (http://en.wikipedia.org/wiki/Accomodati ... nce_reflex). The problem is when you have to force your eyes to focus at a different depth to what is natural and your eyes will automatically try to do by reflex. This will be basically every object close to you. The only way I can think that this can be realistically overcome is to have pupil tracking that dynamically adjusts the focus depending on the divergence, so everything would be in focus at the depth that you are looking at.

[Randomoneh]

That's the thing - I don't think it would! Even if you trick the eye eliminating all the clues, you still won't be able to focus at "fake Moon" an inch from your eyeball - even if it was a perfect representation and your eye is perfectly still. There is an explanation for this in physics - behavior of the photons and the way lens of the eye bends those photons. Still can't figure it out though.

I disagree. IF the rift does actually make your eye focus at close to infinity (accommodation), then any object that has the separation to make your eyes diverge to almost parallel, then the two will match up and your accommodation reflex will appropriately make you naturally focus at the correct depth (http://en.wikipedia.org/wiki/Accomodati ... nce_reflex). The problem is when you have to force your eyes to focus at a different depth to what is natural and your eyes will automatically try to do by reflex. This will be basically every object close to you. The only way I can think that this can be realistically overcome is to have pupil tracking that dynamically adjusts the focus depending on the divergence, so everything would be in focus at the depth that you are looking at.

I agree with your IF. But that's with Rift optics taken into account. Discussion was stuck at the optics of the eye, without any external lenses - that is - on basics.

[foisi]

This is simple optics, every point of an object cast rays of light in every direction. If the object is far away your eye will only catch a small angular portion of the rays for each point due to the opening of the pupil, beyond a few meters this angular portion is so small that the rays are considered parallel. The eye lens has a nominal focal length set to the eyeball diameter, making parallel rays to converge to a single points on the retina.

img1.png

Now if the object is near, the rays coming from each point of the object are no longer hitting the lens eye in parallel and then the image of each point is spread on the retina.

img2.png

The eye lens is able to modify its focal length (it's called the accomodation) but it is limited and the brain automatically knows when you are accomodating to a short distance that the object is near.

img3.png

With a converging lens between the object and the eye and if the lens is set at its focal length to the object, the rays coming out of this lens are parallel. Then the eye lens is able to make a sharp image on the retina without accomodation.

img4.png

I hope it helps

[Bretspot]

Great write-up! Thanks!