Your Digital SLR and Light Sensitivity - dummies

By Doug Sahlin

Your digital SLR camera has an option to determine how sensitive the camera sensor is to light. Digital cameras are the same as film cameras in that light sensitivity is determined by ISO rating. The advantage of a digital camera is that you don’t have to change film to change ISO ratings.

When you increase the ISO rating, you increase the camera’s sensitivity to light, which means you can shoot with faster shutter speeds in low light situations. Increasing the ISO setting also increases digital noise, which is prevalent in shadow areas of your image or in large areas of similar color, such as the sky in a landscape picture. Digital noise doesn’t look good and degrades the quality of your image. If you own a high megapixel camera with a sensor that is smaller than a 35mm frame of film, the images are more susceptible to digital noise when you increase the ISO setting. You also end up with more digital noise when you take a picture with a shutter speed slower than 1 or 2 seconds.

If you own an image-editing application like Photoshop Elements or Photoshop, you can purchase a plug-in to clean noisy images.

When you increase ISO, you run the risk of creating an unusable image. How far up you can crank the ISO depends on the camera and its age camera. The sensors on newer cameras are more efficient and produce less noise than older ones.

The only way to be sure is to take test shots of the same subject in the same lighting at every ISO setting on your camera. Make sure you have some shadow areas in the scene you’re photographing. Download your test shots to your computer, open them in your image-editing application, and zoom in to 100 percent. Digital color noise shows up as tiny specks of color in the shadow areas, and luminance noise shows up as gray clumps in the shadow areas. When the amount of visible noise in an image is unacceptable to you, note the ISO setting and never exceed the next lowest ISO setting on your camera.