Beecher's Handouts >

Exposure > 10 - ISO

Again, the sensitivity of the sensor to light is called ISO.

ISO is the International Standards Organization.

They set standards for manufacturers to follow, such as the diameter of DVD discs.

A smaller ISO number, say 100 or 200, means the sensor is less sensitive to light.

You need lots of light to use a low ISO.

However, the quality of the photograph is better.

Higher ISO settings, such as 400, 800, 1600, are increasingly more sensitive to light.

Higher ISO settings enable you to photograph with less light.

But, the quality decreases as the sensitivity increases, due to noise.

Noise in digital photography corresponds roughly to grain in film.

Noise consists of specs of inappropriate colors (color noise) and specs that are brighter or darker than they should be (luminosity noise).

When using higher ISO settings, noise will be increased.

Noise is most visible in areas of a photograph that have a similar color or tone, such as shadows.

Many cameras will increase the ISO setting automatically if the light is dim.

If you prefer to change the ISO setting yourself, use your camera menu to disable this feature.

Here are some of the reasons for using different ISO settings.

Situation	Use Lower ISO	Use Higher ISO
Not enough light		•
Need to use a faster shutter speed, such as when using a zoom lens at 300mm		•
Want highest quality blacks, such as when doing night photography	•
Want the best color	•
Want less noise	•

The photograph below was taken at an ISO setting of 200.

The lower photograph was taken at an ISO setting of 1600.

ISO 200

ISO 1600

You can see degradation in the color in the bottom photograph.

In the enlargements below, you can better see this deterioration in color fidelity.

You can also see the increase of noise, most easily seen in the shadow area.

ISO 200

ISO 1600

ISO Setting

Numbers

Attributes

Low

50, 100, 200

Less sensitive

Less noise

High

400, 800, 1600, 3200

More sensitive

More noise