It has often been said that is better to show rather than just to tell. In that spirit, sometimes I find it useful to put together little interactive visualizations on the Web to illustrate an idea.

Just this week I was trying to explain to some colleagues an idea I had about eyewear made from mirrors that lets you see to the left with your left eye, and to the right with your right eye. The question I was trying to address was how big your “visual aperture” can be. In other words, when is it like looking through a little peephole, and when is it like looking through a nice big pair of glasses?

Not surprisingly, the nearer you place the mirrors to your eyes (the “eye relief” of the device), the greater the visual aperture. But at some point the eye relief can become too small — if the mirrors get too near to your eyes it will make you uncomfortable.

The smallest comfortable eye relief is probably about 12mm (about half an inch). I created this little visualization to show how eye relief relates to visual aperture.