Telescopic sights are favored for obvious reasons – it is impossible to see the kill zone of the furthest targets clearly with the naked eye. Another advantage of high-magnification scopes is their ability to act as a simple range-finding tool. At very high magnifications, most scopes have a very shallow depth of field, and one can accurately focus on a series of targets at known distances and mark the scope for future reference. In competition you simply focus on the target and deduce the distance from the marks you made on the scope's focus control.