I was afraid I would have problems being a variable ND with rare effects, and zero problems. Neither on the corners, nor at ND400, the truth is that a pleasant surprise for its price. It may have a little green tint, but with a correction of nothing in the Premiere I fixed it, between 5 and 10 points on the dye tab towards magenta and you're done. Highly recommended, you just need to have a cap like the ND2 and ND32 models that are the ones I usually use.

I got to try this filter for my Sigma 17-50, and the result is really amazing. The product looks great in its really great quality packaging and easy to carry in your bag.
The photographic performance is at a high level at a low price. I find the tongue very interesting, it allows you to have better grip during work.

I purchased the K&F Concept Variable ND Filter Neutral Density ND2-ND400 (9 stops) with Rotating Ring to be able to use a fast ND with different densities.
The packaging is very well done, solid and space-saving container. The glass filter is light and the ring to increase/decrease the density is smooth. It has no end stop lock.

To test it best I tried it with three different lenses on the Nikon D750 camera (full frame): 20mm, 35mm and 85mm.
- 20mm: in the photos taken with the filter there is no particular loss of sharpness, it introduces a slight hot dominant that can be easily solved in post-production. As far as the X-shape problem is concerned, it is quite marked using the filter beyond the marked ring. Instead, using it within the marked marking, the problem is little present. See image attached.
- 35mm: in the photos taken with the filter there is no particular loss of sharpness, it introduces a slight hot dominant that can be easily solved in post-production. As far as the problem is concerned, X-shape is not as marked as in the previous one, but there is a vignetting especially in the use with maximum effect. See image attached.
- 85mm: in the photos taken with the filter there is no particular loss of sharpness, it introduces a slight hot dominant that can be easily solved in post-production. As far as the X-shape and vignetting problem are concerned, they are not relevant. See image attached.

Optically, the filter is well made and provides excellent results, but I would have preferred a start and end run with lock in order to avoid possible mistakes. Also considering that K&F produces other types of filters but with magnetic connection, I think it could be a further plus for this filter.

The price/performance ratio is correct based on the performance provided.

I attach more photos of the packaging and two shots to the sea.

I absolutely LOVE this filter. It stays on my zoom on my camera all the time!

The handle to change filter level is easy, the filtering itself looks great and lets you get that perfect shot without switching filters. We took a trip this weekend and this filter never left the lens. If you take pictures outdoors, do yourself a favor and pick this up. No fiddling with any filters in your bag. Just turn dial it in and go.

Very surprised by the quality of the filter, it's from the professional nothing to say. The materials are good and the glass super. The adjustment wheel is very smooth and makes it easy to change the density of the filter. No need to have 4 different filters. possibility to shoot video in full day at the largest aperture. I love it!
It also comes with its small carrying case which is very sturdy and makes it easy to carry without fear of scratching

K&F Concept is synonymous with quality. I already had other filters in kit, albeit quite old and with several years of service behind me. By virtue of my imminent photographic journey, I decided to opt for something new, always relying on them. I will tell you in detail what, in my opinion, are the pros and cons of this new product of theirs.
First of all, the packaging is really great: the box is made of very strong cardboard, impossible even to fold, and then the magnetic opening is very pleasant. The filter is stored in a leatherette case with magnetic closure and not plastic, which gives the product a finish that we can call 'premium'. Inside, wrapped in a protective bag, the filter. It is a fairly heavy piece, already to the touch it gives a great impression. The body is made of aluminum, the glasses are of excellent finish. Very thin (and this is good because this reduces any loss of sharpness), waterproof and scratch-resistant. Very pleasant (and very useful!) the orange little thing you need to change the intensity of the filter itself: the only drawback is not having a limited stroke during rotation, but it's not a big deal, since the limitations ND2 and ND400 are indicated right on the end of the filter itself. In any case, the filter was built in such a way that, even if you go beyond the limits, the annoying 'X' shadow does not show up. For the time being, I had the opportunity to try it only in the city on a somewhat ugly day, in the coming days I hope to integrate this review of mine with other shots in the mountains.
Who is the filter addressed to? Surely for those who love landscape photography or for those who want to do long exhibitions in the city (remaining within the limits of 9 stops): of course, the product is not the cheapest on the market, but that's enough try it for a while to understand that it's worth every penny you spend. I'm not a photography

The filter is of good quality and fills the desired expectations.

Works fine on my canon lens. I don't use ND's much but nice to have in my kit just in case especially now that I live in a much much brighter place. (sotuhwest more sun)

This is a great product. The packaging is super and it sets onto the lens excellently. I love it!

Nice product