K and F Concept® filter, slim HD neutral density grey filter, size: 37 mm. Multiple adjustments possible, fader variable ND filter, from ND2 to ND400 adjustable filter plus cleaning cloth for lenses

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.

This works great on my BMPCC and with the 12mm Samyang lens I have :D

I am using this ND Filter for my sony alpha a6000 with kit lens. product quality is very good but unfortunately it doesnt seem to fade properly with the kit lens I have. Check out the picture. Maybe I dont know how to use this filter. Any advice? I have given this product 4 starts only because of the quality of the build.

A good starter ND filter. It's helped me out on several shooting occasions. Would recommend for someone looking for something basic that does the job.

"The filters are double-threaded, so you can stack your lens cap and other accessories as needed."They are double-threaded but the thread has a larger diameter. I can't attach other filters and the lens cap do hot hold in place.Also, there is the 'black X' problem on the higher settings.