Many optical devices utilize refraction in order to perform various functions, such as lenses. The most common type of lens we see is the converging lens, which is what telescopes and microscopes use. The converging lens, also known as the convex lens (because it curves outward), does exactly what its name implies. It refracts parallel rays of light so that they would converge (meet) at the focal point. It would also refract rays of light that passes through the focal point (on the same side as the object) parallel to the principal axis on the opposite side. Rays of light passing through the optical centre (middle of the lens) will continue to travel forward seemingly uninterrupted.