2: "Correct Exposure"

I still haven't been able to get good examples that demonstrate the importance of learning to use your camera in manual mode. I am eager to move on so I will briefly say that in order to consistently create both correctly exposed and creative photographs, you must use the manual setting on your camera. The do-it-all auto setting will not always produce a good picture, which often leads to frustration. This is not to say that learning to use the manual settings is not at times also frustrating, but it will pay off as you become more efficient at it.

Vintage DeSoto in Teton, Idaho

This brings me to the topic of this post: correct exposure. There are 3 fundamental parts to a photographic exposure. They are shutter speed, aperture and ISO. These are often referred to collectively as the photographic triangle.

Shutter Speed: How much time the camera's light sensor (film) is exposed to light. It is expressed in seconds or a fraction of a second (1' or 1/60).

Aperture: The circular opening that controls how much light is allowed to enter the camera and the depth of field of the exposure.

ISO: Controls how sensitive the light sensor is in the camera. Bryan Peterson describes the ISO as the number of worker bees that are sent out to collect light and then bring back to the camera. The more bees you have, the quicker all the light is gathered and brought back. Unfortunately, as you increase the ISO, or the number of bees, you also get more "noise" as they return to the camera, which results in a grainy photo.


A correct exposure is obtained when these three settings are balanced with one another. If the ISO is increased, then the aperture and/or the shutter speed must be changed to maintain a correct exposure. Think of a three seated teeter totter. It would be shaped like a peace sign without the circle around the edge (see pic below). When this teeter totter is flat with the ground it is causing a "correct exposure" and everybody on the totter would be at the same height. If a lighter person was to get on one of the seats then the other two seats must be sat in by a combination of people that balances out the teeter totter to again be flat with the ground. This is how a correct exposure can be obtained with any combination of shutter speed, aperture, and ISO.

photo credit