I purchased the K&F Concept Variable Neutral Density ND Filter ND2-ND400 (9 stops) with Rotating Ring to be able to use a fast ND with different densities.The packaging is very well made, solid container and not bulky. The glass filter feels light and the ring to increase/decrease density is smooth. It has no end stop block.To test it at its best, I tried it with three different lenses on Nikon D750 (full frame) camera : 20mm, 35mm and 85mm.- 20mm: in the photos taken with the filter there is no particular loss of sharpness, it introduces a slight warm dominant easily solved in post-production. As for the X-shape problem, it occurs quite marked using the filter beyond the marked ring. On the other hand, using it within the marked marking the problem is little present. See attached image.- 35mm: in photos taken with the filter there is no particular loss of sharpness, it introduces a slight warm dominant easily solved in post-production. As for the X-shape problem, it does not occur as pronounced as in the previous one, but vignetting is present especially when using it to maximum effect. See attached image.- 85mm: in photos taken with the filter there is no particular loss of sharpness, it introduces a slight warm dominant easily resolved in post-production. As for the X-shape and vignetting problem, they do not occur to any great extent. See attached image.Optically, therefore, the filter is of good workmanship and provides excellent results, I would have preferred, however, a start and end with blocking so as to avoid possible errors. Considering also that K&F produces filters of other type but with magnetic attachment I think it could be an additional plus for this filter.The quality/price ratio is correct according to the performance provided.I enclose additional photos of the packaging and two shots at the sea.

I had been meaning to buy a variable ND filter for my 24-70f2.8l for a while. When I heard about K&F filters; having tried a 3xnd filter kit pack that I was impressed with; especially at the price. I looked at K&F's other products and found this more than reasonable price ND filter and had to give it a go.

The filter is shipped from China; so its not something to order if you are in a rush - but when it did arrive I was blown away by the quality of the presentation. The filter was packaged inside a well designed; expensive looking, cardboard outer package and then a hard plastic inner with a foam sheet to allow it some protection.

On opening the pack one disadvantage to this filter immediately manifested itself; the front element isn't 77mm so your lens cap won't go back on the lens with the filter mounted. The filter mounted smoothly onto my lens. The variable darkness is achieved by rotating the front element; as you would a circular polariser. The K&F filter spun smoothly but with enough resistance to keep the darkness you set so knocking it won't change the setting. One disadvantage to the design is the filter doesn't have coded ND values so there is a bit of guesswork to get the right exposure for stills.

I tried the obvious and took an image of a plain white wall at various ND settings; and there was some minor differences in the brightness of the photo - it was a bit lighter at the edges of the frames. At its darkest on long exposures; the 6d went red shift but this is correctable in Lightroom (and made much easier if you use a colour checker passport.) If you zoomed in on the plane white background you could see some variations in darkness; and ultimately pixel peeping at maximum darkness a mesh. That said taking pictures of something more interesting than a wall the effect was lost in the detail of the image.

I rarely shoot video so for you dear reviewer; I shot some test video of the same white wall. I don't have any fancy video editing software and just watching the video back in lightroom; the darkening effect was pretty uniform across the photo. As with stills if there were any criticism it is very minor and that the corners show up brighter than the centre of the frame. The majority of the frame being uniformly dark. There was no patterning showing in the video.

Using a standard ND filter definitely gave a more even darkness to stills but I am planning 3 long trips this year and carrying 5 ND filters everywhere felt like a chore. Now I just need one. If i could I would ding 1/2 a star for the front element size not being 77mm but its a minor inconvenience in the scheme of things.

I bought this filter to reduce the amount of light entering through the camera lens and to improve the overall look of outdoor video. The filter lets me control overexposure and it works very well. The filter attaches easily to my camera lens. The filter also come in a protective plastic case and a cleaning cloth which is a nice touch. I’ve come to expect good things from the K&F Concept product range and this is no exception.

I tried this filter on my Sigma 17-50 and the result is really amazing. The product looks great in its really high quality packaging and is easy to carry in your pocket. The photographic rendering is of a high standard for a low price. I find the tongue very interesting, it allows a better grip at work.

This is a great filter,Have several k&f filters and the quality is fantastic,Overall a recommend buy

Good quality product with very good metallic feel.

Made the purchase receni so I'm still testing it.

One thing I am worried about is not to over spin it as from other reviews I have seen some of them distort the image.

Quality, Glass, stop selection. Excellent filter optically superior, image quality, and light control superb.

If you know who this brand cap is it will fit this filter. I just so happen purchase much lens from a buyer who included this cap with it and it totally fits perfectly. But your normal cap will not.Anyway I love the filter it does a great job just be aware of the cross viniette.

I like this ND filter a lot.

very surprised by the quality of the filter, it's professional nothing to say. The materials are good and the glass superb. The adjustment wheel is very fluid and makes it easy to change the density of the filter. no longer need to have 4 different filters. ability to shoot video in broad daylight at the widest aperture. I love it! it also comes with its small carrying case which is very solid and allows you to transport it easily without being afraid of scratching it