ISO

Definition of ISO

Is the scale used to measure film speed or how sensitive the film is to light. ISO stands for “International Standards Organization”. They have set a standard measurement for film speed. In digital photography this is sensors sensitivity to light.

ISO and Exposure

The higher the ISO the more sensitive the sensor will be to light. The advantage of shooting with a higher ISO is that you can shoot in less light such as when you are in doors. This allows you to shoot with a smaller aperture and a faster shutter speed.

If you need to increase your Depth of Field so that more of your subject is in focus you will need a smaller aperture. This means you will need to either choose a slower shutter speed or increase your ISO.

If your shutter speed is too slow and your subject is moving or you can’t hold the camera steady enough to get a clear image, you can either choose a bigger aperture or increase your ISO.

ISO and Noise

The down side of a high ISO is that you will see more noise so your images will be lower quality. Depending on your camera and your preference, the ISO that gives you an acceptable amount of noise will be different. You will find that an ISO of 100 is considered normal and has a low amount of noise.

On my first digital camera an ISO of 400 or more would be too noisy for what I like. On my newer SLR I find that I can have an ISO of 800 or more would be too noisy. Every camera is different and sometimes noise is unavoidable.

Long shutter times also have an effect on noise. This is because sensors pick up stray light, especially at high an ISO.

Conclusion

High ISO allows you to take photos in less light as well as use slower shutters speeds and smaller aperture. This comes at a cost of having noisier images.

Getting a good quality image at the right exposure is achieved by getting the correct balance of ISO, shutter speed and aperture. You need to know the pros and cons of adjusting each setting.