Variable ND filters are primarily used when filming, as long exposure times must be used there. In order to have the right exposure at all times, it is important that you can adjust the ND filter. Inexpensive variable ND filters usually have a yellow tinge. This, of course, falsifies the white balance and the image effect. Unless you want it that way. I still like to use variable filters though. Especially for long exposures on water. But I've often been annoyed by the falsified color effect. The ND filter reviewed here is clearly not one of the cheap filters. It also comes in a very nice case when it arrives and it even has a handle that allows you to adjust it very comfortably on the camera. As you can see from the pictures, the color effect does not change. Aperture, shutter speed and ISO were the same in each case. Only the filter was adjusted. I think you can easily see the quality of the filter there.
In general, I would like to warn against turning on the filter too firmly or slightly crooked or using it at sharply changing temperatures. It happened to me several times that I couldn't get the filter off anymore. This was then only possible with the appropriate filter clamp.
I didn't have any problems with this one though.
I really like it. But that should be the case, as it also costs significantly more than the inexpensive league.
5 stars.

I love it! Just buy it!!

Delivery was very fast. The filter is well made. Instantly screwed on the optics and tried it out. Make its darkening without an X image, as a stroke from min to max. Color image is almost without color cast and is very close to that if it were without a filter. TOP. The only thing you can complain about (it's probably heavy from various optics and their threads) is that the control lever does not point upwards when screwed on. It also works without the lever. The autom. Focus, as with my Sony AX100 camera, can sometimes be lost when set to dark.
Still, I highly recommend K&F, even though it costs more than most. Cheap filters can't keep up with that at all.

The first impression of the ND filter is very good, the materials and workmanship look high-quality, the thread runs smoothly in my lenses and the adjustment itself is very pleasant. I really like the fact that the adjustment range is limited in both directions by a stop, so that accidental overturning is prevented.
The filter also does a good job in other respects, I was unable to notice any color cast or irregularities in the darkening in the entire adjustment range.
The price of currently 94.99€ is not particularly cheap, but in my opinion it is absolutely justified.

There are filters with infinitely variable adjustment options. They're good, no question about it. But if you want to reproduce very specific - exact - settings, an ND filter with latches is better suited. Because if you've made a recording with a specific ND set, you can make all kinds of other settings, but when you need it, you can easily have the same desired setting. Exactly the same one! I can therefore recommend the filter - regardless of whether you are a professional or an interested amateur.

When it comes to photography, I'm more of a layman. The filters from K&F Concept have always been praised and recommended by various well-known photographers. I was able to test this filter here. Top workmanship. Top quality. Turning is slow, but that's okay for me. Better that way than it slipping all by itself. The price is of course not low but you get a lot in return. I think the optical performance is great. All in all 5 stars.