[david_ar]

> but it is neat to see it actually work.

Your brain does this all the time - the resolution of your eyes is actually quite poor compared to what you perceive (as much as a 25x difference). It's quite easy to demonstrate:

> For the most impressive results -- I guarantee you will be amazed -- use a dim room with no light apart from the computer screen; a pretty strong effect will still be seen even if the room has daylight coming into it, as long as it is not bright sunshine. Cut a slit about 1.5mm wide in the card. On the screen, display http://www.inference.org.uk/mackay/itila/Files.html

> Stand or sit sufficiently far away that you can only just read the text -- perhaps a distance of four metres or so, if you have normal vision. Now, hold the slit vertically in front of one of your eyes, and close the other eye. Hold the slit near to your eye -- brushing your eyelashes -- and look through it. Waggle the slit slowly to the left and to the right, so that the slit is alternately in front of the left and right sides of your pupil. What do you see? I see the red objects waggling to and fro, and the blue objects waggling to and fro, through huge distances and in opposite directions, while white objects appear to stay still and are negligibly distorted. Thin magenta objects can be seen splitting into their constituent red and blue parts. Measure how large the motion of the red and blue objects is -- it's more than 5 minutes of arc for me, in a dim room. Then check how sharply you can see under these conditions -- look at the text on the screen, for example: is it not the case that you can see (through your whole pupil) features far smaller than the distance through which the red and blue components were waggling? Yet when you are using the whole pupil, what is falling on your retina must be an image blurred with a blurring diameter equal to the waggling amplitude.

-- p553 of http://www.inference.org.uk/mackay/itila/book.html