Lens converters are used for modifying the focal length of the on-camera lens. They screw on to the end of your camera lens and give your lens added magnification. If your lens converter is 2 it will magnify your lens's focal length by that amount, so a 50mm lens will now work as a 100mm lens. Because converters are attached to your on-camera lens, any optical problems the converter or on-camera lens may have could be magnified by the combination of the two. These problems could include lens flare, ghost image, field curvature and aberration. Because of this, you should only use a lens converter if the on-camera lens cannot reach the desired focal length. Some converters will block the camera's flash sensors, so flash will be unavailable and some may also block the viewfinder. Converters start at about $50.