Unfortunately, the double vision method works only for close objects relative to the base distance of our eyes.

If the relative distance of the dot from our eyes (Y) to the base distance (X) becomes greater the former double vision of the blue dot transforms into a single vision. This means stereopsis is not possible anymore and we are thus not able to sense the different distances of the object as it is seen in two eyes — we are just too far away now.

If a stereo picture is taken of a large, distant object Y such as a mountain or a large building using a normal base X it will appear to be flat. This is in keeping with normal human vision - it would look flat if one were actually there although our brains will make it 3D; but if the object looks flat, there doesn't seem to be any point in taking a stereo picture, as it will simply seem to be behind a stereo window, with no depth in the scene itself, much like looking at a flat photograph from a distance.

This problem affects stereoscopic photography more than in real vision. If you want to take a photo of something that is just too large to fit entirely on your lens — like a building, a mountain, a landscape or a city panorama — the only way is to get farther away from the subject Y and thus loose the stereo effect. Furthermore, we sometimes wish to get closer to particular object but we can’t — like a ship on the sea, an animal or the clouds.

We could conclude that it’s just impossible to sense depth in distant clouds. But obviously clouds are also as three dimensional as is a mountain this is because our brains fill in the detail. Luckily, even in photography, we are not only able to bring back the depth, we are also able to make it visible in a way that we have never seen it before by changing the base distance X.

This is called Hyper Stereo!