Home » Visual & Performing Arts » Photography » Exposure: Getting it Right Everytime, Part III

Exposure: Getting it Right Everytime, Part III

© Wendy Folse

In the previous two articles on controlling exposure, we have covered various ways to use film choice and shutter speed in order to get the correct exposure settings. In this article, we will talk about the third way, and possibly the most popular way of controlling exposure by using the aperture setting to control the amount of light. The aperture setting controls the amount of light that reachs the film plane in order to expose the film. This corresponds to the circular opening in the diaphragm and is marked with the f-stop numbers on the barrel of the lens. This is what most people associate as the f-stops.

When we talk about gaining an f-stop or losing a stop, it is this principle that we are referring to. The shutter speed is marked in parts per second. The aperture settings are marked as f/5.6, f/8, etc. In between each f-stop marking is considered a half-stop, so that if you want 1/4 less light to enter you can set the f-stop marking between two whole f-stops. When you open one full f-stop (go to a smaller number)you are doubling the amount of light that enters through the diaphragm. When you stop down or close one full f-stop, (go to a larger number) you are decreasing the light by half. Remember, half down and double up.

Aperture

In several previous articles, we have covered the use of aperture to control the exposure in very creative ways. If it helps go back and re-read those articles. Aperture as it pertains to getting the correct exposure refers to the size of the opening of the diaphragm. This is what controls how much light is allowed to enter and expose the film. The shutter speed controls how long the diaphragm remains open and the aperture refers to how much it opens. Remember, both the aperture setting and the shutter speed setting control the total amount of light or exposure.

Shutter speed + Aperture = Total Exposure (Film speed refers to how much total exposure the film is capable of recording.)

When the aperture is opened, the f-stop number is lower. When the aperture is closed down, the f-stop number gets larger. This confuses people perhaps more than anything thing else. A simple trick to help you remember the concept is to think of the diaphragm as a pizza and the f-stop number as the number of slices. Don't over think it. If a pizza is cut into 11 slices then the slices are smaller. If it is cut into four slices, then the slices are larger. The f-stop numbers are based on fractions.