A first method, followed and supported by many people, provides the repetition of our human anatomy with a side by side camera system. This system is often used for shots, where objects are not close to a camera, like with landscape or on a helicopter. IMAX-3D® uses this kind of technique, that is very similar to the first stereoscope of 160 years ago.

Basically, some techniques continue to reply the human anatomy with 2 side-by-side lenses. The parallel view method uses two images not more than 6,5 cm which is the average distance between the two eyes. The viewer looks through the image keeping the vision parallel.

This method could be, at first, logical, but it forgets an important element of our physiology: the limit of human vision for very close shots. Observing closer objects, we see them as a overlapped images, if we stare at the background without making a correction with the parallax angle.

Our stereographers always use this instruments that are very precise.
Thanks to experience, we realize that if we have a scene with a lot of object, closer and farer, we don't know where the attention of the audience is driven to. Probably there are a lot of point of attention. Where I can use the convergence?
We have to come to a compromise if we have close or far objects in the same scene. Our brain has the ability to processing or interpolating images and it's able to provide for the issues that come from our two eyes if we have 2 cameras in fixed position. This cause a great effort and fatigue for the brain and eyes in feature film.

But there's a solution for this issues with great results, only with precise gears for example Stereo Rig that doesn't have the limitations of a side-by-side system.