Avoid Digital Noise
Digital noise is comparable to the “grain” you sometimes notice in film photography, as you see here in this noisy photo. Not only do noise and film grain look somewhat similar, but they are also caused by similar factors.
Both are accentuated by high ISO levels, for example. ISO is a measure of your camera’s sensitivity to light, which you can increase to take photos in low-light situations. You’ll always have some noise in your photos, even at your camera’s lowest ISO; but the higher you crank the camera’s ISO, the more noise that results. Long exposures are also major contributors to noise: The longer the exposure, the hotter your camera sensor gets–and all that heat contributes to digital noise in the final image. It’s rarely a problem in daylight, but long exposures at night can fill your photos with noise.
So how do you avoid digital noise? In general, shoot with the lowest ISO possible. You might need to bump up your ISO when you’re shooting indoors without a flash, for instance, but don’t crank it all the way to ISO 1600 when ISO 800 might do. Just increase the ISO until the shutter speed is fast enough to take a sharp photo, which is usually something like the inverse of the focal length.
Here’s an example: If the lens is set to 100mm, you can probably get a fairly steady shot with a shutter speed of 1/100 second. Likewise, though longer exposures can lead to extra noise, you can fight back by turning on your camera’s built-in noise reduction. Many cameras have an noise reduction feature that kicks in automatically or is applied to only certain types of noise. If none of these features works for you or is available in your camera, you can always use your image-processing software to help reduce the noise.