Vision is arguably the most compelling human sense.
Words and stories and sounds allow us to imagine strange beasts and faroff worlds, but seeing
makes us truly believe they exist.
And that's why we place so much effort into correcting the optics of our eyes when they
don't work - whether with glasses or contact lenses or surgery.
But if you're in a pinch, bleary-eyed or missing your glasses, there's a simple trick that
will allow you to see clearly - just make a tiny, tiny hole using your fingers, look
through it, and the world will become clear again.
This works no matter how blurry your vision is -- take off your glasses and give it a
try!
Amazing, right?!
But to explain this wizardry, we just need to remember how seeing works.
Light travels outwards from a source, bounces off of objects in its path, travels into your
eye and onto your retina, where it forms an image.
If your eye had no lens, light from a single source would hit your retina in lots of places
and result in a smeared-out mess - which is exactly what happens when I take the lens
off of my camera.
A lens focuses that spread-out light back into a single point, corralling it into a
crisp image on your retina.
And after a little excitation of light-sensitive nerves and interpretation from your brain,
you see.
But wait!
When we look at an object, the background and foreground are usually blurry, because
a lens can only focus light coming from one distance away.
If an object is too near or too far, its light will again be spread out on your retina leaving
you with a blur.
Fortunately, muscles in our eyes allow us to accommodate by squeezing the lens, which
changes its focal length so we can see at different distances - except when we can't,
or when our lenses become damaged - in which case we need glasses.
Unlike a lens, a pinhole or other small opening can focus light coming from ANY distance:
because it's such a small opening, it only allows light to come through in one place,
and thus in only one direction from any particular source.
So there's no blur, and everything is in focus!
If you're familiar with photography, this is why using smaller and smaller apertures
makes everything in your photo come into focus.
Of course, small openings like pinholes and camera apertures create crisp images by blocking
rather than focusing light, so the images are much darker -- which is a major reason
why we use lenses rather than pinholes for glasses, telescopes -- and eyes.
And yet, in a pinch, looking through a tiny hole made with your fingers can help
you see.
Now do you see why?