Whoa! Big question! I don't think I can get into ALL of the
similarities and differences, but here's a few to get you started...
Both the human eye and a camera use something called a lens. In
fact, they both use the same type of lens - a converging lens.
Converging lenses are like the ones in magnifying glasses - they work
to make an image look bigger. This is why you can see the details in
something even if it's on the other side of the room. One thing about
lenses is that they can only focus on things that are the same distance
away from them. This is why your eyes can focus on things that are
close to you or far from you; just not at the same time. Cameras are
the same way - you can only focus them on things that are the same
In the camera, the lens focuses the light onto a piece of film. The
film has chemicals in it that basically trap the image on it, making it
permanent. Instead of film, your eye uses something called a 'retina.'
The retina has lots of little tiny things called 'rods' and 'cones' all
over it. These are basically tiny antennae that tell your brain about
the light that hits them. The rods tell your brain if there's light in
a certain spot or not (a bit like a black and white photo) and the
cones tell your brain what color the light is.
There is one spot on the retina, though, that has no antennae at
all. This is the spot where the nerve leaves your eye to go to your
brain. At this spot, you can't see anything at all - it's called your
'blind spot.' This is one of the reasons that you have two eyes; what
you can't see with one eye you can see with the other. Unlike your
eyes, cameras have no blind spot, so they only need to have one lens.
Another important thing about seeing light is that you have to be
able to control how much light gets in... otherwise, you couldn't see
things in a brightly-lit room because you'd be overwhelmed by how much
light there is. Your eye controls how much light gets in by changing
the size of the pupil - the dark spot in the center of your eye. The
more light there is, the smaller your pupil becomes, and the less light
gets in. Many (but not all) cameras also can adjust to let different
amounts of light in. This way, your outdoor pictures don't look washed
out and your indoor pictures don't look too dark.
An interesting thing that I learned about pupils is that your pupil
will also change size depending on what sort of mood you're in. But you
sure can't tell the mood of a camera just by looking at it! Is it happy
or is it sad? Hard to say...
There's lots of other similarities and differences between the eye
and the camera, but I'm not going to try to explain them all. For more
information, you can check out How Stuff Works
on the web. They have LOTS of good information on all sorts of things about both the eye and the camera. Good luck!
(republished on 07/29/06)