No doubt you have heard that one of the most important things about taking a good photograph is getting the proper exposure, and that to get that exposure there are three settings on the camera that need to be considered. These three settings are: Shutter speed, Aperture and ISO. Many people trust the camera to select these settings to get a properly exposed image, but are often disappointed with the results. Here is a description of what I mean by each of these terms:
- Exposure- The amount of light that the film or digital sensor receives during a shot.
- Shutter Speed- How much time the film or sensor receives light.
- Aperture- The opening within the lens that determines how much light passes through the lens to the sensor. The smaller the aperture (or opening), the larger the f stop number will be.
- ISO- How sensitive the film or sensor is to the light it receives.
- And most importantly, Properly Exposed- the amount of light the film or sensor receives during the shot to achieve the results that you the photographer want to get.
The three settings (shutter speed, aperture and ISO) and their relationship to each other is sometimes called the Exposure triangle.
I have struggled to find the right analogy to express the relationship between these three settings so that I could explain it to my wife and others. For people like me who are comfortable with mathematical equations, it is like this:
with A = Aperture, I = ISO, S = Shutter Speed and E = Exposure. I you adjust one part, like increasing your shutter speed, then you have to adjust either ISO, aperture or both to still get the proper exposure.
This isn’t a particularly good way of explaining exposure, especially to a young person that may struggle with math, so I have come up with this explanation:
A person wants to get a good overall suntan. To do this will depend on three things: how sensitive the person’s skin is to the sun, how long they are out in the sun and what strength sunscreen they use. The person’s skin sensitivity is like the ISO. The higher the ISO, the more sensitive the film or sensor will be to light. How long the person lays in the sun is the equivalent to the shutter speed. Finally the strength of the sunscreen is like the aperture. The higher the SPF of the sunscreen, the less UV light reaches the skin, and the smaller the aperture (higher f stop number), the less light reaches the film or sensor through the lens.
Remember, it is you that will decide what the ‘proper’ exposure for your images are. Understanding these settings will help give you creative control over your images to express what you envision.
Here is the same shot with 3 different exposures. Which is correct? It all depends on what you want
Text and Images © Ted Griffith 2014
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