Sigma 28-300mm f/3.5-6.3 Macro Lens for Pentax SLR Cameras It incorporates 2 pcs of Low Dispersion SLD glass. It also has 4 pcs. Of Aspherical lenses to produce a high level of optical performance. This lens has a minimum focusing distance of 19.7" (50 cm) in all focal lengths. euipped with a macro mechanism for close-up photography at 300mm telephto with a reproduction ration of 1:6 this lens is eqipped with a "zoom lock" to prevent the zoom setting from being changed inadvertently.