The Science behind Stereoscopes
The stereoscope has many advantages.
It uses positive curvature magnifying lenses with the focal point of the image changed from a relatively short distance to a virtual distance of infinity. This reduces eye strain by focusing the eyes consistent with the parallel lines of sight. The image on the card or paper is magnified, allowing a wider field of view and the ability to examine the detail of the photograph.
In addition, the viewer provides a partition between the images, avoiding a distraction to the user. The main advantage of side-by-side viewers is that the brightness of the image is maintained so the image can be presented at a very high resolution and in full color.
The ghosting associated with polarized projection when techniques like color filtering are used is completely eliminated.