Aperture is one of those words that scares a lot of people.  It’s something that a lot of us know is there but don’t want to deal with.  After all, that’s why we bought an automatic camera.  But aperture is something that every photographer should be aware of, amateur or not.  It is one of the cameras functions that set out limitations for every photo we take.

The aperture in a camera is a function of the lens.  It works the same way that the iris of our eye works.  If you haven’t already experienced this phenomenon in science class then grab a flash light and go to a mirror.  First turn out all the lights and wait for a few seconds.  Turn the lights back on and look into the mirror.  Your pupils should be wide open.  Now, quickly, shine the flashlight right into your eyes.  The pupils will close up pretty quick.  This is because your eye is monitoring how much light it lets in, taking only what it needs.

This is the exact primary function of a lens’s aperture.  An automatic camera will have a light sensor that measures how much light is entering the lens.  In a situation where there is a lot of light it will close the aperture to a finer point because it doesn’t want to over expose the picture.  For photos taken in doors or even at night, the aperture will be opened up.

This function of the aperture works hand in hand with the camera’s shutter.  Imagine that the camera has an option to keep the shutter open—thereby exposing the film or CCD to light—for anywhere from a hundredth of a second to an entire second.  That means the shutter can open and close really fast or really slowly.  If too much light enters the camera during any one of these scenarios the picture would be exposed too much.  Now let’s get back to the aperture.  If the camera’s aperture is opened wide then a lot of light can get in and the shutter won’t have to be open as long.  Conversely, if the aperture is closed to a fine point then not as much light gets in and the shutter will have to be open longer.

Before the days of automatic exposures a photographer had to do a bit of math to determine the best way to balance these things.  These days the camera does most of the work for you.  But it isn’t always right!  Why?  Because the aperture also affects the focus.

Imagine a billion rays of light racing into a lens.  The narrower the opening, the more focused those rays will become.  In practical terms this means if you took a picture of a person with a wide open aperture then the person may be in focus, but everything in front of them and behind them may be blurry.  The more the aperture is closed, the finer the light entering the camera becomes and, in turn, more things get focused.  All of a sudden the person is sharp as is the fence behind them and the tree, etc. 

The aperture, therefore, acts as both a technical means of taking a photo and a way of adjusting the pictures aesthetics. 

Note as well that in photography the aperture is represented by numbers known as F-stops.  The higher the F-stop is, the more the aperture is closed.