I have been wrestling with how to present this information, because there is so much already available. It is photography 101, the basics, plain and simple. My goal is to present some more in depth, deep dive information to really get people thinking about photography in a different way. I am going to start by introducing exposure value.
The exposure: what is it? How is it controlled? Most cameras have some form of a light meter to gauge how much light is in a scene. Another way to express this is with the words: luminance or exposure value. These are essentially measurements of how bright or dark a scene is. A camera can capture a certain range before things are completely black or completely white. Somewhere in between completely black and completely white is middle tone grey. The actual value for middle tone grey is 18% grey.
Exposure value (EV) is based on this scale of luminance. A camera is essentially trying to make everything a middle tone grey. The range of a scene, however, can vary anywhere from pure black to pure white. Digital cameras show this information in the histogram. A light meter has a scale of plus EV and minus EV with the middle being zero. This zero point is where the exposure value is calibrated to achieve middle tone grey.
Underexposed scenes will tend to lose information in shadows and blacks. This is referred to as clipping. Clipping is when the exposure value is insufficient to capture information. Overexposing a scene can also result in clipping in highlights and whites. The goal is to have the sensor capture a scene that is not completely black nor completely white, rather more toward the middle tone grey range. Again, this is where the needle reads zero on the scale.
There are essentially three ways to control the exposure value: aperture, shutter speed, and ISO. Each one of these settings controls how much light reaches the sensor to create the exposure. Aperture is the physical opening of the lens that light passes through to reach the sensor. Shutter speed is the duration (time value) that light is allowed to reach the sensor. ISO (was referred to as ASA for film speeds) is an increase of the sensor’s sensitivity to light.
The combination of aperture, shutter speed, and ISO is often called the exposure triangle. This is due to the balancing act of changing these settings to achieve the correct exposure value. The exposure triangle can also be used to create certain aesthetics in photographs. I will be doing a series of posts that dive deeper into each setting over the next couple weeks. Stay tuned!