And the bigger or smaller hole will affect the amount of light entering the camera, striking the film, CCD or CMOS. A certain amount of light is required to give a correct focus... something that is not too bright or too dark. Since throughout the day, and in door, the amount of light available is not the same. So the camera has to determine what is the shutter speed, and size of aperture needed to get that required amount of light on the film, CCD, CMOS. Big Aperture/hole more light, and vice visa... So... If you want some blur background thingy, you set a small F-stop (Big aperture)... So more light is getting in right? So what to do? Open the hole for a shorter period... which means a faster shutter speed. If you Set camera at Aperture Piority... You choose the Aperture (Big hole BLUR blur or small hole sharp sharp) and the camera will decide what is the shutter speed required to correct expose the image... In other words, allow the right amount of light in.