The three light management controls in our cameras are shutter, aperture and ISO. Each has a secondary, or “side” effect that relates to sharpness in our pictures. Understanding what those side effects are, and learning to detect which is causing the blurring in our images is the first step to getting sharp pictures in the first place.
Motion blurring is the result of movement of either the subject, or the camera, or both while the shutter is open. If the shutter is open for a short time, the blurring is less. If it’s open a long time, the blurring is greater. Think of shutter speed as cutting “slices of time”. The thinner the slice, the less motion blurring you’ll see in your image. Motion blurring can easily be confused with Focus blurring, except that motion blurring usually has a direction (imagine the camera moving from left to right or up and down). Also, blurring due to camera movement should affect every pixel in the image the same, wheras focus blurring often affects only part of the picture.
Focus Blurring sometimes happens just because we fail to focus properly berfore taking the shot. Focus blurring can also be the result of a shallow “Depth Of Field”. Certain combinations of lens length, distance from the subject and wide aperture settings can create blurring in the foreground and background.
Noise is sometimes mistaken for blurring, but really it’s a pebbly distortion that’s associated with high ISO settings. Because higher ISO’s are used to get better exposures in low-light situations, shots after dark or in dimly lit rooms tend to be noisy. Interestingly, noise in film cameras happens because of a chemical reaction in the film. Noise in digital cameras happens because of electronic static from solar winds (the ISO adjustment is really just an amplifier, not unlike a volume control in radios). Despite this difference between film and digital, noise looks almost exactly the same in both film and digital finished images.