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[benitomuso]

  The operating principle used for my Stereo 3D MOD is Anaglyph. It consists on having two images tinted with different colors (in this case Red / Cyan) that have been taken from slightly different points (with a distance similar to the separation between our eyes) so when they come to your eyes again, you receive a perception similar to the real one you have with objects.

I will reproduce here some coments I made to Raptor where I explained why some users don't clearly see "3D everywhere":

  "Look, as far as I know, it is absolutely normal. This is a matter in real life too. The perception of objects which are close (let´s say elements of the cockpit or in your own desk while you read this), is naturally deep, because they appear quite different in position to our eyes, separated less than 7cm. On the contrary, the distant objects seem to be quite the same, because 6.7cm of distance between eyes, is nothing for objects 50m ahead of you. So we are "forcing" as we do in external view, a much wider eye separation, which is not natural, but in this way we have a more interesting and spatial experience. But when you do that, the closer objects, become "too separated" and you cannot compose them, they look "shifted". Our natural eye configuration is quite good to perceive and meassure distances (apart of the focus problem) between 20cm and some tens of meters. If you put an object (you can try yourself with your finger) closer than 20-15cm, you will see two shifted images. It is the same phenomenon as in cockpit when you adjusted the separation for external."

  The articles in Wikipedia about Anaglyph and Stereo 3D are excellent, quite specific and detailed. I stronly suggest you to read them:

http://en.wikipedia.org/wiki/Anaglyph_image

http://en.wikipedia.org/wiki/Stereoscopy

  From Stereoscopy, I consider is very useful to reproduce this part:

Base line selection
For general purpose stereo photography, where the goal is to duplicate natural human vision and give a visual impression as close as possible to actually being there, the correct baseline (distance between where the right and left images are taken) would be the same as the distance between the eyes.[34] When images taken with such a baseline are viewed using a viewing method that duplicates the conditions under which the picture is taken then the result would be an image pretty much the same as what you would see if you were actually there. This could be described as "ortho stereo."

An example would be the Realist format that was so popular in the late 40s to mid 50s and is still being used by some today. When these images are viewed using high quality viewers, or seen with a properly set up projector, the impression is, indeed, very close to what you would see if you were there.

The baseline used in such cases will be about 50mm to 80mm. This is what is generally referred to as a "normal" baseline, used in most stereo photography. There are, however, situations where it might be desirable to use a longer or shorter baseline. The factors to consider include the viewing method to be used and the goal in taking the picture.

Longer base line for distant objects "Hyper Stereo"
If a stereo picture is taken of a large, distant object such as a mountain or a large building using a normal base it will appear to be flat.[35] This is in keeping with normal human vision, it would look flat if you were actually there, 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.

One way of dealing with this situation is to include a foreground object to add depth interest and enhance the feeling of "being there", and this is the advice commonly given to novice stereographers.[36][37] Caution must be used, however, to ensure that the foreground object is not too prominent, and appears to be a natural part of the scene, otherwise it will seem to become the subject with the distant object being merely the background.[38] In cases like this, if the picture is just one of a series with other pictures showing more dramatic depth, it might make sense just to leave it flat, but behind a window.[38]

Moon stereo from 1897 taken using libration. Anaglyph, red left.For making stereo images featuring only a distant object (e.g., a mountain with foothills), the camera positions can be separated by a larger distance (commonly called the "interocular" or stereo base) than the adult human norm of 62-65mm. This will effectively render the captured image as though it was seen by a giant, and thus will enhance the depth perception of these distant objects, and reduce the apparent scale of the scene proportionately.[39] However, in this case care must be taken not to bring objects in the close foreground too close to the viewer, as they will show excessive parallax and can complicate stereo window adjustment.

There are two main ways to accomplish this. One is to use two cameras separated by the required distance, the other is to shift a single camera the required distance between shots.

The shift method has been used with cameras such as the Stereo Realist to take hypers, either by taking two pairs and selecting the best frames, or by alternately capping each lens and recocking the shutter.[35][40]

It is also possible to take hyperstereo pictures using an ordinary single lens camera aiming out an airplane. One must be careful, however, about movement of clouds between shots.[41]

  Regards,
                         Pablo