Three dimensional displays using binocular disparity techniques are widely used. Binocular stereoscopic images can produce
a mismatch of distance between plane of focus (accommodation) and plane of fixation (convergence) of the observe?s eyes.
The viewing distance, i.e. plane of required focus, is generally greater when looking at a large screen than when look at a
small display. In this study the fusional ranges of the binocular three dimensional image are compared when viewing a large
screen (75inch,projection type TV display) at a distance of 350cm and when observing a small display (2linch CRT) at a
distance of 100cm. We found that the fusional range was more extended on the larger screen than the smaller display.
Accommodative responses were measured when looking at the 3D image. Accommodation does not remain in the plane of the
display but changes to the stereoscopic distance of the 3D image fixated by the observer. The changes required when using a
longer viewing distance were smaller than those measured with an a short viewing distance. These results suggest the longer
viewing distance reduces an unnatural feeling of viewing 3D images due to the mismatch of distance between the planes of
accommodation and convergence.
Accommodation response time was measured after looking at stereoscopic 3D images. Far-to-near response time was
longer than before viewing these images. The results showed that the viewing stereoscopic 3D images provided the observer's
visual system with different type of stimuli from these experienced in normal viewing.