What Is an ISO Setting?

The name "ISO" comes from the Greek word "Isos," meaning "equal."

In film photography, ISO setting specifies the film's sensitivity to ambient light. In digital photography, the ISO setting indicates the image sensor's sensitivity to light. The higher the ISO setting is, the more sensitive the film or sensor is to light.



ISO setting is also known as ISO speed. The term "ISO" refers to an international standard set by the International Organization for Standardization (ISO).

Range of ISO Settings

The most common ISO settings are 100, 200, 400 and 800, but some advanced cameras have settings as high as 3200.

Lower settings are appropriate for daytime photography with full sun. Higher settings, such as the 400 to 800 range, are ideal for outdoor evenings, or low-level indoor lighting. A higher ISO setting results in a faster shutter speed, which is better at capturing fast movements (e.g., sports or dancing).

Adjusting the Camera's ISO Setting

On cameras that allow manual settings, you normally change the ISO setting by rotating a dial or pressing a series of buttons, as specified by the camera manual. Cameras set to "Auto Mode" will automatically adjust the ISO setting to the current lighting conditions.

Effects of ISO Settings

A digital image comprises millions of tiny squares. Certain squares occasionally appear as a different color, producing "noise." An ISO 100 setting results in clean, well-defined images with little grain or noise. An ISO 800 setting allows you to photograph in low light, and capture faster movements, but typically results in a slightly grainy or noisy image.

The same is basically true of film; the higher the ISO setting, the grainier the photo tends to be.

Breaking the Rules

Experimenting with a higher ISO setting can add a gritty or textured look to finished images, according to the Digital Photography School. Photographers wishing to create or enhance a specific mood can adjust their ISO settings to achieve this and other unusual effects.

References

• International Organization for Standardization: Discover ISO: ISO's Name
• Digital Photography School: ISO Settings in Digital Photography
• Digital Photography School: Moving Toward Manual Settings: Understanding ISO (A Beginner's Guide)
• SLR Photography Guide: What is ISO Setting on Your Digital SLR
• Cameratown: Quick Guide to Understanding ISO "Speed"

Resources

• Picture Correct: Photography Exposure Basics
• Digital Photography School: Use a High ISO to Create Grainy Shots