Photography 101 - Part 1 - Understanding Exposure

Picture an ordinary garden hose. One end of the hose is attached to the spigot on the house and the other is lying in a bucket. Your goal is to fill the bucket with the exact amount of water that fulfills your creative vision. If you don’t add enough water, it will be under filled (under exposed) if you add to much, it will be over filled (over exposed). With water in a bucket, it doesn’t get much more complicated. No matter how you fill it, you still have just water in a bucket.

With photography, the how is just as important as the how much. Let’s take a skinny hose and turn the water on. The water barely comes through and it takes a while to fill the bucket. That’s a slow hose. Now replace it with a fat hose. Turn the water on just the same amount but look how fast it comes through. This is aperture. Open your lens up wide and you have a fat hose. Stop it down and you have a skinny hose. With this, you can control how fast you fill up your bucket with light… I mean water.

With either the skinny hose or the fat hose, you can fill the bucket the same amount by changing how long you leave the water on. If you have a skinny hose, you let the water run longer than if you have a fat hose. This is shutter speed. A fast shutter speed turns the hose on for an instant and doesn’t let much water go through. A slower shutter speed lets the light flow for a while.

The other thing to consider is your water pressure. Some faucets can barely muster a drip while other gush. With a lot of pressure, you can fill that bucket up even if you have a skinny hose and don’t keep it turned on very long. This is ISO. Crank up the ISO and you crank up your water pressure.

Aperture (hose thickness), shutter speed (how long you let the water flow), and ISO (water pressure), work together so you can fill your bucket the same amount but in different ways. A fat aperture combined with a fast shutter speed may get you the same amount of light (water) as a skinny aperture and a slow shutter speed. If you crank up the water pressure, you can get the same amount with both a skinny aperture and a fast shutter speed. Whenever you change one of the three, you can change the others to end up at the same place… a bucket full of water.

But, as I said above, in photography how you fill your bucket matters. Next time in this column, we’ll discuss how these different ways affect the final look of your photo.