Compare this to the water bucket scenario. You have a 1 gallon bucket (compare to film sensitivity) that you have to fill in 2 minutes. You open your faucet to 1/4 open (aperture) and let the water flow for 2 minutes (shutter speed) but the bucket is only half full at the end of 2 minutes (underexposed). So to fill the bucket you have to change one of the variables. Either the faucet opening (aperture) or the time of water flow (shutter speed). Since we said that you had to fill the bucket in 2 minutes you will have to change the faucet opening (aperture). We need twice as much water in the same amount of time so we open the faucet to 1/2.

   Hopefully you have been able to follow along and I have not made to confusing so far.

Things to consider when setting your exposure controls.

   When you change your aperture or your shutter speed you are changing 2 qualities of the image other then proper exposure, Depth of field (aperture controlled) and motion blur (shutter controlled).

   With larger aperture settings (smaller numbers) you get less depth of field or less area in sharp focus. Therefore f2.8 would have less area in sharp focus then f5.6. I have a related article on this site about selective focus you should read for a better understanding. Click here to read it.

   With shutter speed you control how much motion blur there is in your image. By selecting the proper shutter speed you can pan the camera with a moving car to get a sharp car in the image and everything else would be blurred by motion or you could stop a tennis ball as it crosses the net by using a fast enough shutter speed. One thing to remember about shutter speed is that I believe camera shake ruins more pictures then anything else. This comes from hand holding a camera at too slow of a shutter speed. As a rule of thumb, never hand hold a camera at a slower shutter speed then the reciprocal of the length of the lens. In other words, if your using a 100mm lens then never hand hold your camera at a shutter speed slower then 1/100 of a second. Use a tripod.

   Now take these considerations and go out and practice using them. It doesn't matter what you photography, just do it at different settings and study the results.