Very observant! That happens to me if I go very cross-eyed and for whatever reason don't get the images fused. I think it's due to minor muscle imbalance that causes the eyeballs to rotate slightly unless they get feedback from the brain telling them not to do that.MacroLuv wrote:Interestingly, while trying to cross my eyes I got another illusion - two photographs does not look parallel but forming an angle like "V".
(Many years ago in college, I had a crazy work schedule that made me stay awake for 34 hours straight, then put me a physics class at 8:30 am. I would know that I was about to fall asleep, when the blackboard would suddenly appear to clone itself, and the two copies would rotate inward as if to spill the professor's writings onto the floor. But I digress...)
I speculate that your eyes are doing exactly what they are normally supposed to do: converge and focus at the same time onto the same point. Unfortunately, with crossed eye stereo, that normally correct behavior becomes a problem. When you converge enough to properly overlap the two images, the focus shift can make them so fuzzy that they never fuse properly. Ironically, young flexible eyes will have more trouble with this than old stiff eyes (see "presbyopia").
To get around this problem, you have to somehow break the connection between convergence and focus. But I have no more ideas at the moment about how to accomplish this. Sorry!
Perhaps someone of our other binocular stereo people can chime in with new ideas?