The smc FA 645 120mm f/4 Macro Lens from Pentax is a medium format, manual and autofocusing, short telephoto/portrait prime lens that provides a 35mm equivalent focal length of 96mm when used on a Pentax 645D or 77mm on a film 645 camera. The super multi coating (SMC) significantly increases the amount of light transmission. The lens offers a 1:1 magnification ratio and focuses as close as 15.4". The focus limiter can be used to set the focusing distance range for increasing the speed of the autofocus. The maximum aperture of f/4 can be stopped down as far as f/32. The lens was developed using computer-assisted optical design technology for a high degree of precision. It uses a floating mechanism and an independently-moving aperture mechanism. It also features extra-low dispersion (ED) glass to correct for chromatic aberrations, helping to deliver sharp imagery with high contrast and clarity throughout the focusing range.