Photo Hacks: For beginners: Understanding exposure in 3 steps. Step 3: understanding ISO.

There are 3 factors which determine the exposure of a photo: ISO (International Standards Organization), aperture and shutter speed.

ISO is the level of sensitivity of your camera to available light. The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera.

The ISO scale typically starts at 100, and continues to double: 100, 200, 400, 800, 1600, 3200, 6400. Each step between the numbers doubles the sensitivity of the camera. For example, ISO 200 is twice more sensitive than ISO 100. It means that it needs two times less time to capture an image.

At lower ISO numbers photographs will be clean and crisp.

With increased sensitivity, your camera can capture images in low-light conditions without using a flash. But higher sensitivity adds grain or “noise” to the pictures. Digital photography is composed of lots of little squares (the grain) which come together to create an image. Sometimes (at higher ISO numbers) those little squares in the image become slightly visible and this is referred to as “noise”.

Every camera has so called “base ISO”, which is the lowest ISO number that can produce the highest image quality, without adding noise to the picture. On most of the cameras the base ISO is typically 100 – 200. As a general rule, the lower the number, the better the quality of the photo.

How to determine what ISO number to use?

ISO 100-200: great for shooting outdoors in daylight. Your photos will have the most clear details and the best quality.

ISO 200-400: good for slightly darker conditions (in the shade, at the cloudy day or indoors with bright light).

ISO 400-800: good for shooting with a flash indoors.

ISO 800-1600: good in low light conditions where flash is prohibited.

ISO 1600-3200: it’s used in extremely low light conditions, it’s impossible to avoid “noise”.

A low ISO number would give a low exposure and a high ISO would give a high exposure. This is much easier to demonstrate using photos. The photos are displayed in the following order: auto mode, 100, 200, 400, 800, 1600, 3200, 6400. The aperture (f/4.5) and shutter speed (1/320) remain constant, only the ISO is changing, so you can clearly see its effect on a photo.

The ideal exposure is shown in the fifth photo, which was taken at ISO 800.