Aperture sights, also known as peep sights, range from the ghost ring sight, whose thin ring blurs to near invisibility (hence ghost), to target aperture sights that use large disks or other occluders with pinhole-sized apertures. In general, the thicker the ring, the more precise the sight, and the thinner the ring, the faster the sight.[1] The image to the right shows a shooter's eye view of the sight picture taken through large and small diameter apertures. The large diameter aperture provides a much brighter image of the target, and the ghosting of the rear ring is evident. The smaller aperture, while providing a much darker image of the target, provides a much greater depth of field (see pinhole camera for an explanation of this effect), yielding a much sharper image of the target.[1] The theory of operation behind the aperture sight is that the human eye will automatically center the front sight when looked through the rear aperture, thus ensuring accuracy.[1]
These sights are used on target rifles of several disciplines and on several military rifles such as the M1 Garand, the No. 4 series Enfields and the M16 series of weapons along with several others. Peep sights are very effective in poor lighting, and have found favor with a few hunters who hunt in heavy cover.[citation needed]
