Let there be light!

Now that we've gotten the basic idea of how photography works, we're well on our way to moving into the digital realm. But, before we move on, I think it's important to first get a good general understanding of how the human eye functions. So let's put our physcist caps back on, and talk a little bit about light and the human eye.

Despite the constant nod to the great evolutionary wonder that is the human eye, our eyes are far from being perfect. The interesting thing is that, as you'll see, the limitations of our eyes make things easier to create technologies that are not perfect, but good enough for us mere mortals. =) So let's start with the basics.

The mechanics of our eyes are quite similar to that of the camera (Hmm... I suppose I should say that the other way around ^^;). We have the pupil which is equivalent to the aperture, and its size is controled by the iris which contracts and expands to control the amount of light that is let through. At the back of our eyes is the retina that contains a bunch of photoreceptor cells that take on the role of the film. There are two types of light-sensitive receptors.

The first type of receptors, found mostly in the center of the retina, is called cones. Cones operate primilary under high light conditions, and although they are not very sensitive to lights, they take on the important role of granting color sensitivity to our eyes. Next we have the rods which primarily operate under low light conditions. Rods are much more sensitive to light than the cones, but can only sense gray-scale. The amount of each type used at any given point in time depends heavily on the amount of light present.

So, let's talk about lights. Human beings can only interpret a small portion of the entire electromagnetic spectrum. The current guess is that we have evolved through the years of being exposed to the sun as our primary light source, and so we've become accustomed to being sensitive to wavelengths of the photons found in sun light. This range of colors are referred to as our visible spectrum and spans from lights that h