Announced December 2003, the SMC DA 16-45mm f/4 ED AL lens was Pentax's first lens specific for DSLRs with APS-C size sensors with a reduced image circle in comparison to their 35mm lenses during that time. The SMC DA 16-45mm f/4 ED AL also maintains constant maximum aperture throughout the zoom range. Its focal length is equivalent to 24-67mm focal length in a 35mm format. The SMC DA 16-45mm f/4 ED AL concerts Extra-low dispersion glass element and two aspherical elements promoting top quality imaging production. The lens offers Pentax's Quick-shift focus system ensuring swift shifting from autofocus to manual focus using the focus ring.