The average interocular of humans is considered to be about 65mm (2.5 inches.) When this same distance is used as the interaxial distance between two shooting cameras then the resulting stereoscopic effect is typically known as “Ortho-stereo.” Many stereographers choose 2.5” as a stereo-base for this reason.

If the interaxial distance used to shoot is smaller than 2.5 inches then you are shooting “Hypo-stereo.” This technique is common for theatrically released films to accommodate the effects of the big screen. It is also used for macro stereoscopic photography.

Hyper-stereo refers to interaxial distances greater than 2.5 inches. As I mentioned earlier the greater the interaxial separation, the greater the depth effect. An elephant can perceive much more depth than a human, and a human can perceive more depth than a mouse.

However, using this same analogy, the mouse can get close and peer inside the petals of a flower with very good depth perception, and the human will just go “cross-eyed.” Therefore decreasing the interaxial separation between two cameras to 1” or less will allow you to shoot amazing macro stereo-photos and separating the cameras to several feet apart will allow great depth on mountain ranges, city skylines and other vistas.

The trouble with using hyper-stereo is that scenes with gigantic objects in real-life may appear as small models. This phenomenon is known as dwarfism and we perceive it this way because the exaggerated separation between the taking lenses allows us to see around big objects much more that we do in the real world. Our brain interprets this as meaning the object must be small.

The opposite happens with hypo-stereo, where normal sized objects appear gigantic. (Gigantism.)

http://dashwood3d.com/blog/beginners-guide-to-shooting-stereoscopic-3d/index.html

http://3d-con.com/2014/files/NSA2014-MACRO1.pdf

http://nzphoto.tripod.com/stereo/macrostereo/macro3dwindows.htm

http://nzphoto.tripod.com/sterea/stereotake.htm