This is a TEST REVIEW for the item sold on Amazon with the description: K&F Concept Nano-K Magnetic Filter, CPL Circular Polarizing Filter with Nano Coating for 77mm Lens (Cleaning Cloth Included). This is a CPL filter (polarized light is controlled by rotation around its axis) that is very comfortable to use thanks to its two-part threaded anchor ring and the filter with magnetic outer ring. The threaded ring is installed and then it can be removed with a simple grip and pull on its contour (which has a ribbed texture for a better grip) and to fix it again, then present it on the ring and position it until you find the magnetic pull and its anchor in a well-adjusted position. In terms of performance, they stand out outdoors in good sunlight (indoors and artificial light is imperceptible) and outdoors very shady. Therefore, it is usually useful when shooting landscapes, especially in areas where an area of sky or clouds appears, or where light is reflected in rivers, springs, lakes, etc... or in reflections with a metallic effect. Depending on the orientation in which the ring is rotated, the image becomes slightly darker or brighter, attenuating the sunlight and taking on a greater or lower color saturation (when rotated on the magnetic system it sounds a little like a rubbing squeak, but as is usually used in photo and video recordings, the position is first sought and then the recording is activated, as this does not affect the tone of the recordings). I made an edited video with some image changes in the same shots, with the CPL polarization ring only partially rotated. The images appear with a higher hue but less luminous, which is why it is advisable to adjust the gain of the light meter a little, because if we rotate the ring when we are in manual mode or in the preferred aperture or speed control modes with respect to it, the recording speeds and apertures vary respectively, and personally I like images that are a little more vivid both in colors and brightness, but without annoying reflections. Due to its very good price/quality ratio and its ease of installation and replacement with filters from the same “Magnetic Adapter Ring” magnetic attachment ring system, its thin “Slim” mount that prevents vignetting on square lenses, its good presentation in a protective box and the special cleaning cloth included in the set, my rating for this K&F Concept filter is: “5 STARS” = [* * * * * *]. I hope you find this review helpful, Best regards. The disadvantage that I forgot and that I noticed later is that on CANON lenses with the EF series front caps, they do not attach with the filter installed or with the filter removed, since the filter is a narrow format (SLIM), the retaining tabs of the lens front cover do not engage with the profile of the filter or its support ring. To be able to put the cap on, you must also remove the threaded ring and store the set in the box.