Amazon.com : 52mm Pro Series Multi-Coated High Resolution Digital Ultraviolet Filter for Pentax smc DA 50mm f/1.8 Lens, Pentax DA 18-55mm f/3.5-5.6 AL WR Zoom Lens : Electronics
Amazon.com : Altura Photo 52MM Lens Filter Kit - Includes 52MM ND Filter, 52MM Polarizer Filter, 52MM UV Filter - UV, CPL Polarizing Filter, Neutral Density for Camera Lens with 52MM Filters +
ProOptic 52mm Digital Essentials Filter Kit PRO-FL-52-KIT - Adorama
Phone Lens Kits 37/52mm CPL ND32 Full Color Filter
SmallRig MagEase Magnetic CPL Filter (52mm) 4216
Moment 52mm AntiGlare CPL Filter (600-099) - Moment