I'm preparing example photos for a lecture I'm giving on digital photography at the SparkArts: Digital Arts Festival, October 12, 2007.

These were created to illustrate the noise caused by high ISO settings. One common mistake I see is people setting their cameras to high or auto-ISO, causing noisy images, when they could have created terrific, clean images just by adding a little light to the scene, or letting a little more light into the camera.

ISO controls the gain of your sensor's light sensitivity. Think of it as a volume knob for light. Turning up the ISO boosts the volume of the light, but it doesn't change how much light actually struck the sensor, just like boosting the volume of your stereo doesn't change the volume your music was recorded at.

In other words, if you didn't get enough light in the first place, boosting your ISO is going to brighten the image, but it will also raise the volume of random background noise, which shows up as little multi-colored dots.

Even in a properly exposed high ISO image, you'll find that the image isn't as sharp as it could be. Digital noise obscures fine detail. The image has lower contrast, because raising the noise floor reduces the available dynamic range. Shadows and blacks are not as deep as they could be, and that makes colors appear to be less rich, too.

These examples are straight from the camera with no photoshop, and no level, color, or contrast adjustment. I created two images, and made detail crops from them to illustrate the points.

ISO 3200:

ISO 100:

ISO 3200:

ISO 100:

ISO 3200

ISO 100

As you can see, an ISO boost should be your last resort. So what do you do first?

• Add more light to the scene - turn on a lamp, open some curtains, or set up a flash (off camera!)
• Open your aperture wider (smaller numbers)
• Lower your shutter speed as low as you can go without motion blur from camera shake. For me that's typically around 1/30th of a second, but many people find that 1/60th of a second works better for them.

I don't like to use high ISO settings for my professional images, but never say never. If you have a choice between grainy photos or no photos of a cherished memory, go ahead and boost that ISO!