ISO

ISO is actually technically misleading. ISO refers to a standard defined by the International Standard Organization. It was initially defined for analog film cameras and refers to the sensitivity of the photographic film. Lower ISO's mean that the film needs longer time for correct exposure (also know as slow burn films). Higher ISO numbers indicate that the film needs shorter time for correct exposure. Translating these terms into digital camera has been done only a few years back. ISO for digital camera depends on sensor sensitivity and sensor noise. But the basic concept remains the same, how fast the sensor is able to capture an image with the correct exposure. An ISO rating of 100 is used for normal sunlight and is the default for most cameras. An advantage of digital photography over analog is that the ISO rating can be varied on the fly, rather than rewinding the film, taking it out and putting in a new film with different ISO rating. Usual ISO ratings in digital photography is 100, 200, 400 etc.. (power of 2 * 100). ISO rating is usually used in conjunction with shutter speed and apperture to gain a desired effect.Increasing the ISO rating while keeping the shutter speed and apperture would cause over exposure, which is sometimes done when we are using a camera for specialized photography, especially during night. In that case, make sure that it is tripod mounted, since movement of camera or object can cause blurring (unless that is the desired effect of course). Usually for sports and wild life photography we use a higher ISO rating, since we need a faster response time.