Pentax 600mm f/5.6 smc PENTAX-A* 645 ED (IF) Manual Lens for Pentax 645, Black {49} with Built-In Hood

A (A Star) ED IF:designation for high performance lenses with Extra Low Dispersion Glass and Inner Focusing on long lenses. The IF mechanism moves only a few lens elements while focusing to minimize lens extension, maitain good weight balance, assure smoother focus ring operation and allow a shorter minimum focusing distance. 600mm/5.6 ED IF SMC Pentax A* Weight: 169.6 oz, 5.3 pounds WITHOUT case. 49mm filter size. Minimum Focusing Distance: 16.1 ft (5 m).