This K&F Concept filter is thoughtfully designed and well manufactured out of quality materials. The CNC aluminum rings are a non-reflective matte black finish that easily and smoothly screw into the filter mount of my 24mm Nikkor lens. This filter is a thin mount design and showed no signs of vignetting for this lens.

I like that the five stops of continuously variable ND values are marked on the filter, in stops, with white dots between the extreme ends that are marked for minimum and maximum effect. The adjustment ring turns very smoothly and has just the right amount of resistance so that while easy to turn, it will stay in place where you want it to. The ring only turns between the minimum and maximum points and does not over-travel. The lens mount ring is easy to grip and has some textured areas that make it easy to screw onto the lens without spinning the moving part. The filter adjustment ring has a different texture so it is easy to manipulate by feel without getting the functions confused.

I set up a camera equipped with my 24 mm and this K&F variable ND in place, on a good stout tripod. I did test exposures with no filter and then one shot at each of the demarcated positions. Six exposures taken wide open on aperture preferred automatic. I saw no issues in the final results to blame on the filter. I have owned dozens of filters in my fifty years of professional photography and this is the best filter I have ever used. It reminds me of the very expensive B&W filters that I used to prefer. That said, it is brand new and I cannot predict how well it will stand up to use and age.