The Eyes Have It

Addendum: Mike writes (click here) about cameras that take 1,500 megapixel photographs. Strap one of these babies onto my head and give my eyes a break. Thank you for the information Mike.


Have you ever blown up one of your digital photographs so you can see the pixels, or a film photograph so you can see the graininess? Some are grainy or pixelated even without having to be blown up much. The better the camera (or the better the film) is , the better the resolution of the photo is. No brainer.

This past winter I found myself driving across the Arizona desert and marveling at just how much information the eye was able to take in. On a part of the road with a clear view of the road and terrain 20 miles ahead, I was able to take in probably something like 400 square miles of desert in one glance. And all of it in rich vivid detail. I started thinking about photo resolution and realized that our eyes are pretty damn phenomenal. Of course you can't blow up what your eyes see to observe the graininess of your vision, but a photograph couldn't possibly have taken in all that my eyes could see in the Arizona desert with anywhere near the same level of detail.

I've often wondered since then just what the resolution of our eyes is. I remembered vaguely that our eyes have what are called cones and rods and that these are the light receptors. I had no idea how many of these there were nor what their function was. I assumed one type sensed black and white while the other sensed color, but that was as far as I considered.

I decided this morning to read up on it. I found an in depth article on this ( A Big Look at the Eye ) which told me everything I wanted to know. Our eyes are each 120 mega pixel receptors. The highest resolution digital camera is 39 mega pixel by Hasselblad (this gets debunked above). Most consumer cameras are in the 6 to 8 mega pixel range. Most professionals use 10 to 12 mega pixel cameras. So our eyes are each 3 times as sensitive as the most sensitive camera made (although I wouldn't be surprised if NASA and spy satellites have better), and up t0 20 times as sensitive as the cameras most of us use.

The eyes have 120 million rods and 7 million cones. I read that and figured the rods must be for color since there are lots more colors than there are shades of gray. I was wrong. each of our eyes has a retina with 120 million sensors of shade. These sensors are extremely sensitive - apparently much more sensitive than any sensor in your camera. The 7 million cones are sensitive to color. Cones can see red green and blue - though there are far fewer blue cones for some reason and it is theorized that the brain must compensate for this.

The rods see shades of gray but they see these shades best in blue light. They can't see in red light at all. This explains the apt use of red instrument readouts for night vision. At night your rods are busy in their hyper-sensitive night vision mode and red glowing instruments can't be seen by the rods so they don't lose their sensitivity as they would if they saw white light. It also explains why roses are brighter than green leaves in daylight while the green leaves are brighter in twilight (click here).

Rods are one thousand times as sensitive as cones to light. On the other hand cones provide much higher visual resolution. But cones are more sensitive to movement. Guess that's why we get spooked by something moving in the bushes at night. And rods are more predominant in our peripheral vision so we can see dim stars at the edges of our vision only to have them disappear when we look straight at them.

Our eyes are pretty complex. I've mentioned a few of the things I read that intrigued me. I'm still just as fascinated by our eye's ability take so much in. I think I would really hate to be blind.