A picture formulates at the back of the eye. The amount of light let into the eye helps form the picture depending on how sensitive to light your eye becomes and how much available. During low light conditions your eye increases its light sensitivity. While it decreases at brighter conditions. When you go from a dark room to a bright room, your eyes adjust decreasing the light sensitivity to deal with the brighter room. On cameras this light sensitivity is called ISO.
What is ISO?
ISO stands for International Organization of Standardization. Basically this organization created a standard for the light sensitivity number. This allows you to go from camera to camera using the same numbers for light sensitivity. Instead of saying the whole thing, International Organization of Standardization of light sensitivity, we call it ISO, pronounced eye-so.
ISO numbers typically range from 100-12800 on a camera. Some cameras can go even higher. The lower the number the lower the light sensitivity. While higher the number increases the light sensitivity. In a bright situation, like a sunny day, you could possibly use a lower number. Though in a low light situation, like inside, you might want to use a higher number. Remember that all this depends also on your shutter speed and aperture.
How to use ISO
While being able to increase or decrease the light sensitivity can help get the picture you want, there is something else to remember. The higher the ISO number goes the more grainy the picture looks. A grainy picture is also called noisy. A noisy, or grainy, picture looks like a non-working television covered in white noise. The picture can look unfocused. To avoid the grainy look, I avoid setting my ISO higher than 1600. To keep a clear picture, try not to go too high on ISO. You can also adjust the shutter speed or aperture to let in more light.
ISO helps create the image you wish to capture. For example, on a sunny day if you need a fast shutter speed and small aperture to capture freeze frame sports, you can increase the ISO to keep a clear image. On the other hand, you can lower ISO if you need a larger aperture for a portrait. Shutter speed and aperture with ISO help to create the image you want to capture.
Notice how overexposed the picture becomes as the ISO number increases but the shutter speed and aperture stay the same.
ISO is the camera’s light sensitivity. The lower the number, the lower the sensitivity to light, while a higher number has a greater sensitivity. Since ISO stands for the International Organization of Standardization, you know that the light sensitivity numbers will not change with each camera company. This makes it easier to help others learn and capture pictures. With shutter speed and aperture, ISO creates the exposure triangle. When all three are used you can create beautiful pictures.
Note: The photos used in the example come from my personal collection. Please do not use them without referring back to me.