The Human eye is an organ that can distinguish between 10 million colors.   That does not take into account that some of us have what is known as  "taste" and others are challenged in this area.  Never the less, we are  blessed with having two eyes placed on the front of our heads. This gives  us Binocular vision.  Our two eyes work together with our brain for the  perception of depth.  This skill turns out to be rather handy.   Our eyes  have a pupil, which adjust how much light gets into our eye.  We can see  fairly well in bright Sunshine as well as darkness.  In a very short span  of time our eyes adjust to severe changes in light intensity.  A dynamic  range of about 20 f stops is possible in a healthy human eye.  {an f stop  is a precise measurement of the opening of a camera lens}   So far so  good.  I bet your impressed with yourself right about now.  I'll also bet  that you take your eyes for granted until there is a problem to panic  over.  Then there is something called peripheral vision.  Us humans can  sense movement while looking straight ahead.  Very handy if you are a  hunter gatherer, or driving your SUV on the turnpike.  The human eye is  often compared to a camera lens, and in fact is similar.  Similar, but not  the same.  You see our eyes are attached to our brain.  Once our brain  gets information from our eye, it searches its memory for something to  compare the image to.  We find objects either familiar or unknown based  upon our memory.  In fact your brain can fill in the blanks for you.  It  does this more often than you might think.  You are driving home late at  night, you are on your block.  You navigate your street with the full  knowledge of where the curves are, and where the potholes are too.  Often  you really do not see the detail, you just know where everything is and  your brain puts those puzzle pieces where they belong for you.  We also  have to ability to recall images from memory.  We can see a vivid image of  pure white sand and gentle ocean waves, blue sky, and gulls circling if we  choose to.  Don't forget our dreams, moving picture memories as real as if  they just happened.  Law enforcement authorities are very familiar with  just how unreliable eyewitness testimony can be. There's that brain again filling in the blanks for us. 

Camera lenses are wonderful inventions modeled after the human eye.  They  see lots of stuff.  They are very limited when compared to our eyes.  I  frequently change lenses when photographing a scene.  I'll use 300mm to  narrow and move closer to a subject, and then switch to an 18mm for a wide  view.  My eyes can do this with little effort.  I have to make a decision  about f stop for my camera.  Do I want everything in the photo sharp?   I'll then use a small f stop to gain depth of sharpness.  Do I want to  blur a background?  Then a wide open f stop is the answer.  My lenses  capture everything in their field whether I want them to or not.  There is  a difference between what my eye is looking at and selecting, and all that  is in the field of view of my lens.  When I make a successful photograph  it is because I've taken time to "see" rather than just "look".  Most  times my decision making process involves eliminating subjects from my  viewfinder rather than adding them.  This is due to the fact that my eyes  can zoom in and see a Cardinal in a tree for instance, appreciate its  beauty, be able to describe it in detail, and not know what kind of tree  the bird was sitting in.  My eyes did see the tree, and its leaves.  My  brain discarded unwanted information, and retained only what I was  concentrating on.

I walk several miles a day.  Its good for me.  Walking allows me to be  guilt free when asking for a second bowl of pasta. It also is an  opportunity for me to exercise my awareness muscles.  As I walk I  practice the art of seeing, and being aware of as much as possible.  It  also makes me thankful for the gift of vision.