The focal length changes the angle of view in an image. The longer the focal length, the smaller the angle of view and the greater the magnification.Get more reach with what you have. Check the compatibility of your lens with the teleconverter chart.Check the compatibility of lenses with your camera make and model.See how a lens performed using the Modulation Transfer Function (MTF) Chart Guide. The MTF is just one criterion used to evaluate lens performanc.earn about the state of the art technology put into Sigma lenses to ensure high quality images, Need more information on a lens? Cross reference all the specs using the lens chart.