These newly designed teleconverters feature optical construction that allows them to be used with lenses down to a focal length of 150mm with excellent results. However, they really shine and deliver optimum results in overall definition with focal lengths longer than 300mm. Tamron's teleconverters are designed to maximize the peak performance of the master lens. Relative illumination is significantly improved resulting in better overall contrast and resolution across the entire image field. In addition, chromatic aberration and astigmatism are better compensated for by virtue of the use of higher-grade glass materials and more sophisticated design techniques than used in universal-type teleconverters.