Most lenses’ focal length – or, to put it another way, how far zoomed in the lens is – is the most significant feature. The focal length of a lens is measured in millimeters. There are several lenses that only have one focal length. Prime lenses are what they’re called. Zoom lenses, on the other hand, cover a wide variety of focal lengths. Check the focal length first when you are buying a new camera lens. If you need a variety of camera lenses, you can check Viltrox brand.