The continuously adjustable iris disc enables optimum focus adjustment. By opening and closing the iris, the shooter can see the sharpness and focus of the target changing. The best results are achieved in the range 1.0-2.0. Ranges above 2.0 can be helpful if a shooter has his eye far away from the rear sight, for example when shooting in a standing position. Below 1.0, the iris aperture may appear not perfectly round and unsharp. However, this is just a physical effect which occurs as a result of the small diameter. If you check the iris at its smallest setting with a magnifying glass, you will see that the aperture is perfectly round. These extreme small ranges are barely used.