In order to understand the exposure we need to look at each of them individually. But before we do that, a little something on the side. On the mode dial of your camera where you see the symbols A(v) S M P or Adep there is also a little green square which represents automatic. This is a no no if you want to become a creative photographer. Automatic means that the camera chooses the setting for you and you just point and shoot. Those symbols represent what we call the creative modes. The other little pictures are the idiot modes which we don't use either.
So let's take a look at the three modes of the exposure triangle.
1. Aperture
Aperture controls how much light reaches the sensor. To me the aperture setting is the most important of the three because it allows you to control depth of field or as I like to call it, depth of focus. This allows you to set how much of your image will be in focus. A shallow depth of field is when on a portrait the background is beautifully blurred out with only the person's face in focus. This gives a lovely image image as the background clutter is blurred into an abstract milky kaleidoscope of soft colour. In order to achieve this a small aperture number or f-stop is used. Whether the aperture is large or small is immaterial, what you need to remember is that a small f-stop gives you a small or shallow depth of focus, i.e. only a small portion of the image is in focus as you see in a portrait of a person. To achieve a large depth of focus you do the opposite by using a large f-stop number, i.e. a large portion of the image is in focus as you often see in a landscape photo. This mode is important with creative photography as it allows you to control what is in focus or out of focus. What you also need to know about aperture numbers or f-stops is that a small number lets in a lot of light and a big number lets in a little light. Remember this. Most times I will shoot on the A(Nikon) or Av(Canon) mode as this gives me control of the aperture while the camera selects the shutter speed.
2. Shutter speed
Shutter speed controls the length of time the shutter is open. This allows you to control the sharpness of the image. An action photo needs a fast shutter speed in order to freeze the shot. But if you want it blurred to simulate speed then a slower speed will achieve that level of creativity. When shooting on the S mode the camera will control the aperture while you choose the shutter speed. What you need to remember is that a fast shutter speed i.e. 1/125 to 1/1000th of a second lets in a little light and a slow speed lets in a lot of light.
3. ISO
This is really simple as it controls the sensitivity of the sensor and is a last resort when you can't let in sufficient light with the aperture or shutter speed settings. There are times when you can't select use a wider aperture as this will make the depth of field to shallow so it's necessary to increase the ISO level. The same goes for the shutter speed. The downside is that the higher the ISO the more noisy the image.
Now, how does the exposure triangle work? There are times when you want to take a shot of a wind surfer twisting through the air. This means you need a fairly fast shutter speed. Because he is moving a shallow depth of field won't work as part the surfer may be out of focus so you need a large f-stop number. If you remember, a large f-stop number means less light and a fast shutter speed also means less light. So you have a problem.
The important thing here is that you want a fast shutter speed to freeze the fast action. You can do one of three things. Slow down the shutter speed which won't work as you need to freeze the frame. Secondly, you can increase the amount of light by choosing a smaller aperture f-stop number. This won't work as only a small portion of the image will be in focus. The only thing left to is to increase the sensitivity of the sensor to the available light by increasing the ISO level. This lightens the image and allows your fast shutter speed and large depth of field.
The way exposure triangle works is that it if you change one of the three settings it will affect the others. I must emphasize here that the exposure triangle is most effective when using the manual mode so you have full control of all three settings. By being aware of these three aspects of your photography you will be able to increase your creativity. Happy shooting!
