ISO and The Exposure Triangle

Rounding out the three-part series on the exposure triangle, we arrive at ISO.

This setting is often the most confusing for beginners simply because it is hard to relate to a moving function on a camera. What ISO is referring to is the camera’s (or film’s) sensitivity to light. The sensitivity is related to the user in a number scale with higher numbers increasing the sensitivity. Setting your camera to an ISO of 800 will make it more sensitive than a setting of 200. This also holds true for film with the major difference being that the entire roll of film is consistently the same ISO while digital cameras allow for adjustments between each shot.

ISO carries with it a unique marker, just as shutter speed and aperture does. As ISO sensitivity is increased you will begin to find areas of your images becoming speckled or grainy. What is happening is that a higher setting is introducing noise into the image. Digital cameras adjust the ISO by increasing or decreasing the gain to the sensor and, just as too much gain distorts audio recordings, distortion becomes evident in photography. How much noise and at what setting this becomes evident is dependent on the quality of the camera and how well the processor can handle the gathered information.

The noise artifact does carry over to film but is more often referred to as grain and is sometimes sought after by the artist. Some photographers seek out a specific grain effect for their images and will choose a film that inherently adds grain. It is certainly true that digital artist can choose to capture images with grain but I prefer to take as clean an image as I can and, if I wish to have grain, add it in post processing.

The exposure triangle is comprised of Shutter Speed, Aperture, and ISO. Al three points work together to determine the exposure of any given image. Adjusting any one point on this triangle has an impact on the exposure and another point would need to be adjusted in compensation to maintain an exposure. When it comes to determining what your exposure is to be it may be helpful to remember that every point on this triangle is about gathering the right amount of light to generate your image. Mastering each point will require practice, observation, self-critique, and time. Every photographic scenario requires the photographer to make choices around this triangle to capture a properly exposed image while creating the desired effect. What you as the photographer and artist must choose is the correct combination.

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