The PL-C 52WII 52mm Drop-In Circular Polarizing Filter from Canon is designed for use with the EF 300mm f/2.8L IS II USM and EF 400mm f/2.8L IS II USM lenses, which accept rear-mounted drop-in filters. The filter is rotated from a ring on the outside of the filter mount. You do not have to remove the filter to use it. The glass is secured within a strong metal frame that slips in and out of the rear mount with ease. The degree of polarization can be seen through the viewfinder of your camera as you rotate the filter. Circular polarizers help to reduce reflections and glare by filtering out light that has become polarized due to reflection from a non-metallic surface.
See recent price change history for the Canon PL-C 52WII 52mm Drop-In Circular Polarizing.
Please provide the webpage address of the PL-C 52WII 52mm Drop-In Circular Polarizing product page at the store (the page showing the product and its price).