I don’t know how many times I’ve seen folks post really blurry or grainy photos on Facebook or other social media sites. It’s become so common that I’m amazed and thankful when I see a well-focused and well-exposed photo posted. The makers of those photos probably don’t understand why their phone cameras create such mediocre images, especially considering phones commonly use an eight megapixel sensor. The cause of the mediocrity comes from what the users of those built-in cameras don’t have: control over the triangle of exposure.
The triangle of exposure refers to the three things that DSLR users, and often users of point-and-shoot cameras, can control. I’ll call it the triad from now on.
The first element of the triad is ISO. This refers to the sensitivity of the sensor, and many new to DSLRs may not know that they can change it. The method of changing the ISO depends on the camera model, but the shooting menu usually allows the photographer to change it relatively easily, taking less than a minute. In the film days, we changed the sensitivity of the camera by changing to a different film ASA speed. The American Standards Association (now ANSI) developed that standard in the 1940s. In 1974, the ISO standard combined the ASA and the DIN (Deutsches Institut für Normung) standards. Typically, a photographer would use a 100 – 200 ISO for daylight, and increase it for darker situations. At this writing, DSLRs commonly go up to 6400 ISO, which allows the photographer to shoot in substantially darker settings. So, why wouldn’t a shooter always use the highest ISO rating the camera can handle? The higher the ISO, the greater the digital noise; in this case, noise refers to the graininess or blotchiness of the resulting image. The heat the pixels generate at higher ISO settings causes distortion of the electrical signal that those pixels produce. In film, the higher speed films generated graininess.
Second of the triad is shutter speed. A longer shutter speed allows more light to strike the sensor. A shutter speed of 1/60th of a second lets in twice as much light as 1/120th, for example. But, the longer a shutter stays open, the greater the chance that it will create motion blur. This only makes sense; the longer shutter speed allows more time for the subject and the photographer to move during the exposure. Generally, a photographer not using image stabilization can avoid motion blur with a shutter speed inversely proportional to the focal length of the lens. So, a photographer could hold a 50mm lens stable enough to use a 1/50 shutter speed, whereas using a 250mm lens would warrant a 1/250 speed. The photographer can use motion for artistic advantage, where he or she follow a fast moving subject with the camera, blurring the background. Race photographers commonly use this technique. Star trail photography, such as my example below, also take advantage of motion. In this case, I mounted the camera on a tripod and opened the shutter for about 27 minutes, resulting in the semi-circular trails.
Aperture fills out the final element of the triad. This measures the opening of the lens in proportion to the the length of the lens. As an example, f/2.8 on a 50mm lens would result in an opening of about 17.85mm, whereas the same aperture at 100mm would measure 35.7mm. The higher the f-stop number, the smaller the opening because the f-stop number divides the length by the aperture (f22 for 50mm results in a 2.27mm aperture, and a 4.545mm opening at 100mm). Many photographers tend to open up the aperture to increase the light to the sensor because it creates fewer issues than increasing the ISO or slowing down the shutter speed. Increasing the aperture (smaller f-stop numbers) diminishes the depth-of-field (DOF), which basically means that areas in front of, and behind, the subject will fall out of focus. Like motion, a photographer can use this to artistic advantage. The artistic use of low DOF, or out of focus areas in a photo, is commonly refered to as bokeh, which originated as the Japanese word boke, and commonly pronounced BOH-KAY or BOH-KUH. The downside to using larger apertures to achieve nice bokeh is that the photographer runs the very real risk of getting part of the subject out of focus. This happens most often with subjects very close to the lens, such as macro photography.
So, in order to make your DSLR photography not look like it came out of an iPhone, remember to use the triangle of exposure.