Digital Camera Web Guide - Digital Photography

What is the ISO Setting In Digital Cameras

ISO stands for International Organizationfor Standardization (ISO). The ISO number is a numerical scale representation of light sensitivity. The lower the number, the less sensitive. The higher the number, the more sensitive.

Why is ISO important when taking pictures?
 Your digital camera will take a measurement of the light entering the lens. If the ISO is set to a low sensitivity number such as 100, it will require a slower shutter speed and/or a large aperture (allowing more light to enter the lens) to record the image. On the other hand, if the ISO is set to, for example IOS 800, a more sensitive setting, it will take less time to record the image, therefore it will require a faster shutter speed and/or smaller aperture.

In low light situations, if you set your digital camera to Auto, it will select a higher, more sensitive ISO setting usually.

The Pros and Cons of a high ISO setting.

The Pros of using a ‘faster’ ISO setting (of 400 or more):

• A higher ISO will allow you to take photos at a faster shutter speed than if it was taken at 100 ISO for example.
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  The shutter speed is too slow to freeze the movement in this image. Selecting a 'faster' ISO would have helped.

  Taking photos with a higher ISO setting will help you take photos with less blur which is the result of too slow a shutter speed or ‘camera shake’ – movement of the camera when the actual photograph is taken will result in a blurry photo. The more you zoom in on a subject the more apparent the camera shake. So if you have you use your zoom in low light it’s best to select a higher ISO setting to allow for a faster shutter speed.

• In a low light situation where you may not wish to use the flash, such as at a concert, a party, or at a fireworks display for example, setting a higher ISO will allow you to capture the perfect image with a reduced risk of the image turning out blurry, again due to camera shake.
• Some cameras have the option to select an Auto Hi ISO number, which is good if you know you’ll be facing a low light situation but don’t want to use the flash, or perhaps you like the ’grainy’ effect very high ISO numbers produce. See Cons for more on this.

The Cons of selecting a higher ISO setting:

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  Look how much noisier (grainier) the 3 other pics are compared to the one taken at ISO 100.

  In old photos taken with black and white film (and in colour too) the grainy photos sometimes looked great and the affect could be appreciated, but in the world of digital cameras, as you crank up the ISO you are making the sensor more sensitive to light and this causes ‘noise’. It’s the electronic equivalent to the grain you see in such photos. If you don’t want this you will have to use a powerful flash to make up for the lack of ambientlight, then you may be left with harsh looking photos.

ISO and ASA – what’s the difference?
ASA stands for American Standards Association, there also the DIN number system which was a German standard. There was a British Standard too, but all have either been dropped or moved over to the current ISO system.

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