April 13th, 2015
The third, and last, aspect of exposure is sensitivity. In film cameras, different films have different sensitivities to light. In digital cameras, sensor sensitivity can be changed on demand. This sensitivity is called ISO. Often, low sensitivities (ISO 100-400) are used when light is abundant, and high sensitivities (ISO 4000-12,800). [These values are true for a 5D Mark III, and vary by the camera used) Now, from this it looks like cranking up the ISO is an easy way to get more light. Unfortunately, that's not the whole story. High ISO's confer noise, due to the way that they amplify light hitting the sensor.
Better cameras (with higher quality sensors) confer less noise at comparable ISO levels. This is due to their improved signal to noise ratio. For instance, the 5D Mark III has basically imperceptable amounts of noise all the way up to ISO 1600, and minimal noise up to ISO 6400. The same cannot be said for point-and-shoots, and camera phones, which often see much more noise at much lower ISO values. This makes high ISO values useful, but they must be used with caution, and can result in spoiled shots.
Below is a successive series of ISO levels. The first set is at ISO 100, the second at ISO 4000, and the last at ISO 12,800. Notice the increasing amount of noise across each set. The image to the left in each set is the original, and the one on the right is a cropped version to better isolate the noise differences.
Thoughts on sensitivity? Take a moment to leave your thoughts in the comment section below.
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