ISO is a measure of a camera’s sensitivity to light. It is an important element in the triangle of exposure, along with aperture and shutter speed.

In film photography, ISO referred to the speed of the film, with higher ISO films being more sensitive to light and lower ISO films being less sensitive. In digital photography, ISO is a setting on the camera that can be adjusted to control the sensitivity of the image sensor.

Higher ISO values correspond to a higher sensitivity to light, which means that the camera will be able to capture an image in lower light conditions. However, increasing the ISO also increases the amount of image noise, which can degrade the quality of the image. Image noise appears as grainy or speckled areas in the photograph and is most noticeable in the shadows and darker areas of the image.

ISO can be adjusted on most digital cameras by turning a dial or using a menu setting. It is usually expressed in numbers, with lower numbers corresponding to lower sensitivity and higher numbers corresponding to higher sensitivity. Common ISO values range from 100 to 6400, with some cameras offering even higher values.

In general, it is best to use the lowest ISO possible in order to minimize image noise and maintain the highest image quality. However, in low light situations, it may be necessary to increase the ISO in order to capture a properly exposed image. It is important to find a balance between image quality and the need for a higher ISO in order to achieve the desired exposure.