APERTURE!

The primary function of a camera lens is to capture light. This is achieved by two main components, shutter speed and aperture.  Aperture is the size of the opening of the camera lens and is expressed as F-stop (for example F2.8 or f/2.8). The larger the F-stop number (f/value) the smaller the opening on the lens is going to be and therefore less light will go through the lens (leading to a slower shutter speed). A larger f/value is ideal in situations with lots of light since the lens opening is smaller and less light goes through the lens. The smaller the f/vaule the larger the opening and the more light that will go through the lens (leading to a faster shutter speed). This is ideal in low light situations because the lens opening is larger.
RULE OF THUMB
-large f/value = small opening = less light coming in 
-small f/value = large opening = more light coming in

f-stop = f/6.3      shutter speed = 1/1000 sec.

 
f-stop = f/29      shutter speed = 1/40 sec.

look at the difference in the two photos. one might think that all i did was change the focus but all that i changed was the aperture. the first has a small f/value so the opening in the lens is larger and more light is coming in that is why the shutter speed is so fast. The second has a greater f-value therefore a smaller opening in the lens so less light is coming in and the shutter speed has to be longer.

NOTE!!! DO NOT SHOOT A PHOTO AT LESS THAN 1/60 sec. WITHOUT A TRIPOD OR SOMETHING TO KEEP THE CAMERA STILL. if one does then the photo will most likely come out blurry!! a person can NOT hold still for that long without moving.

Aperture and DOF
DOF = depth of field.
The DOF is the distance in which the objects seen are in focus.
There are times when one would desire a great DOF (where things close to the camera and far are in focus, aka landscape and one wants the greatest amount of things to be focused, crisp) There are also times when one would desire a shallow DOF (when one thing close up is in sharp focus but the back round is blurry and out of focus). By using aperture one can manipulate DOF.
RULE OF THUMB
-Small aperture (BIG f/value) = great DOF
-large aperture (SMALL f/value) = shallow DOF

f-stop = f/5  shutter speed = 1/1600

f-stop = f/11   shutter speed = 1/320 sec

f-stop = f/32   shutter speed = 1/30 sec (note the back flowers are not crisp in focus because i did not use a tripod…ALWAYS USE A TRIPOD when shooting under 1/60 sec)

look at the difference in the photos in the first only the one flower is in focus. In the second a little more is in focus and in the third the most is in focus (had i been using a tri-pod it would be completely in focus). The higher the f/value the more is in focus. again i did not change my focus just changed the f/value

RECAP!!
-large f/value = small opening = less light coming in + great DOF
allows one to use a slow shutter speed (allows one to depict motion) on a sunny day
-small f/value = large opening = more light coming in + shallow DOF
allows one to use a fast shutter speed and isolate the subject by blurring back round.

TEST YOUR KNOWLEDGE!!
put your camera on AV (aperture priority) and take a photo with multiple elements (something in front, middle and back) and change the f/value and take another do this from the lowest f-value to the highest. you might not see the difference on your camera but on the computer you will. so go out and experiment with your new knowledge of aperture!!