Looking through mAny a lens, I can’t help but notice a lot of distortion toward the edges. There’s chromic abberations and warping of the image itself.
But when I’m looking through the lens, I’m also looking through the lens of my eye. It doesn’t appear to have the same problems. What’s up with this? Do I just have a cheap magnifying glass, or do our eyeballs have some crazy reverse-engineerable technology?
It’s kinda hard to see the edge of your own vision. You have to stare straight ahead, but concentrate on observing what is off to the side or slightly behind you. It gets pretty fuzzy out there, so I’d say it is indeed a bit distorted. 'Course, I’m trying to see it out of the edge of my eyes, which means that not only do I have to “look out of the side of my eyes,” I can’t use any part of my trifocals. --wait, I just held my glasses up to the side of my face. Weird.
The lenses in your eyes do reverse the image, as all true lenses do. Your brain does the work of making everything normal again.
Based on a few quick tests on my brother’s eyes I don’t think you really can look out the edges of your eyes, your irises don’t seem to get all the way to the edge. Get someone to pull your eyelids open and watch while you try to look all the way to the left and right (or vice versa) to see. Don’t know if this really explains anything…
Kerinsky
OK, I gotta know. Why is this step necessary?
Umm, when you move your eyeball, the lens moves with it. Trying to see the edge of it’s field of view doesn’t involve looking in a particular direction, but increasing your perception of what is going on at the periphery of vision. AFAIKT there’s no noticiable chromatic abberation or “rainbowing” out there, nor is the much in the way of distortion. The distortion at least is probably there, but with a well designed lens system it can be moved well outside the angles covered by the users visual field. On the other hand, you can look through a loose lens at all sorts of angles that the lenses designer never intended to produce a undistorted image. The lens of the eye has been evolving for a long time and even in primitive trilobites, where the lens is made of a calcite sphere, aligned along the non-birefringent axis, the lens material is doped with impurities to minimize the spherical abberation ! I’ve no idea how the human eye handles chromatic aberation (the change of focal length with frequency) but the lack of rainbows suggest that it does.
I don’t buy the “you can only look at the center of the field” argument. It’s true that the eye has much higher resolution at the center of the field, but the field of vision is pretty big - you can see almost 180 degrees without moving your eyeballs. You’d notice if, for instance, a white streetlamp at the edge of the field became a rainbow, or if a straight line appeard to be curved.
However, the eye isn’t an isolated instrument; the brain compensates for many of the “defects” of the eye, e.g. the fact that the image is upside down. So the brain can and does compensate for the distortion. I’m not sure if it’s possible to compensate for chromatic aberration, but I don’t see why not.
Also, the eye is a far more sophisticated lens than the piece of glass you can buy at a store. If I remember correctly, it’s a non-spherical surface (spherical is easier to manufacture but has aberrations), and even has a varying index of refraction.