Di%3A Digitally Integrated Design%2C is a designation Tamron puts on lenses featuring optical systems designed to meet the performance characteristics of digital SLR cameras%2E%0D%0A %0D%0AThis lens employs an IF %28Internal Focusing%29 system that maintains the overall length of the lens during focusing%2E Uses two LD %28Low Dispersion%29 glass elements that effectively compensate for chromatic aberration%2E Provides high%2Dcontrast%2C outstanding image quality and a soft out%2Dof%2Dfocus background effect%2E Super performance series provides high performance through outstanding design specifications%2E%0D%0A %0D%0AFEC %28Filter Effect Control%29%3A Features the new FEC %28Filter Effect Control%29 function that enhances operational ease of Polarizing Filter use%2E The new Filter Effect Control is designed to rotate the filter to the desired position while the hood is attached%2E This is accomplished by turning the FEC ring that in turn rotates the portion of the filter mount where the filter is mounted%2E