So don't forget that along with f/stop and shutter speed, ISO is an important element of exposure control. When the light level in the scene requires a shutter speed slower than 1/250 second, the camera will automatically kick up the ISO to maintain that shutter speed. Here's how it works: In aperture-priority operation, for instance, choose ISO control and set a base shutter speed of, for example, 1/250 second-meaning that you don't want the shutter speed to go below that setting. Selected Nikon D-SLRs offer auto ISO control, a feature that will maintain a selected shutter speed range. The scale on which that sensitivity was measured was 100, 200, 400, and so on, with a lower number indicating a lesser sensitivity to light. Fortunately, many Nikon D-SLRs, using Nikon's EXPEED image processing concept, are capable of image capture at high ISO settings-800, 1600, 3200 and even higher-without noticeable noise. what is iso in photography Back in the film days, ISO was often referred to as ASA, and it referred to the level of sensitivity of film to light. More accurate it measures the sensitivity of the image sensor. With digital photography, the equivalent is noise. ISO expresses your cameras sensitivity to light. With film cameras, using a higher ISO film, such as ISO 400 to 1000, often resulted in noticeable grain. The solution for both instances: boost the ISO to increase the sensor's sensitivity to light. Or, in the case of photographing a concert performance, the widest lens opening and slowest hand-holdable shutter speed may not enable enough light to reach the sensor.
But when the situation calls for a shallow depth-of-field and, thus, a wide lens opening, and/or a fast shutter speed, that combination may not allow enough light to reach the sensor. In most cases manually setting the f/stop and shutter speed, or using one of the camera's automatic exposure controls (aperture- or shutter-priority, for example) is all you'll need to do.
The ISO setting is one of three elements used to control exposure the other two are f/stop and shutter speed. For digital photography, ISO refers to the sensitivity-the signal gain-of the camera's sensor. High ISO film was called fast film-it required a shorter exposure than a low ISO film. The higher the ISO rating, the greater the film's ability to capture images taken in low light. ISO originally referred to the sensitivity of film-it's "light gathering" ability.
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