I tested the variable gray filter from K&F on a Tamron 28-200mm F/2.8-5.6 DI III RXD lens and a Sony SEL-20F18G, on a neutral white background.
Since I already use fixed ND filters from K&F and am quite satisfied with them, I was curious how this variable filter would perform.

Advantages of the variable gray filter from K&F:
- Significantly less expensive than purchasing multiple fixed density filters.
- Takes up less space and weight.
- When filming, among other things, smooth aperture transitions can be realized without post-processing.
- Pleasant feel.
- Handle for adjusting very well solved.

My conclusion: The filter from K&F achieves good results especially at low stops between 1.5 and 4 f-stops. Beyond that, however, the uneven light distribution at the edges of the image increases. This becomes more noticeable the shorter (e.g. at 20mm) the focal length is. At 10 f-stops, the X-effect then also becomes visible. The color fidelity is not really neutral and has a slight yellow cast, but can be easily corrected afterwards via the white balance in RAW images. An assessment of the set density via the scale on the filter is only roughly possible, which makes it almost impossible to calculate the exposure times manually. However, modern cameras like the Sony a7 series can reliably calculate the exposure time through the filter. To be fair, it must also be said that the aforementioned weaknesses occur to a greater or lesser extent with every variable gray filter. Therefore, my recommendation for ambitious photographers is to rather rely on ND filters with fixed density. In the range of 1.5 to 4 f-stops, however, the variable filter from K&F is quite usable for qualitatively good photo shots. Especially for filmmakers, the K&F should be an attractive filter, at a reasonable price. In my opinion, the disadvantages are less important here. The processing is successful in every respect. The filter can be operated well, without accidentally touching the glasses with your fingers.

Rating: 5.0 from 5.0

Quality of workmanship: ⭐️⭐️⭐️ ⭐️
Variable: ⭐️⭐️⭐️ ⭐️
Suitability for practical use: ⭐️⭐️⭐️ ⭐️
Material texture: ⭐️⭐️⭐️ ⭐️
Price: ⭐️ ⭐️ ⭐️ ⭐️

I was allowed to test the variable ND filter (gray filter) ND3-ND1000 of the brand K&F Concept.
For me it was the first contact with a variable filter.
Accordingly, I was over the large width of the setting of 1.5 - 10 f-stops by just moving the hand lever.
As an amateur photographer, I use a variety of filters up front that I carry with me on occasions like our vacations. It may not be the same for others, but I always sweat blood when changing screw-on filters in the middle of the field, scrupulously careful not to paw at them with my fingers. As of now, the camera case is a bit lighter and it stays with a single filter. I like that already very much.
But the filter was also already delivered in a valuable box, in which there is a noble bag as storage for the filter. I guess every hobby photographer is very happy about such a noble gift. But before buying, you need to know the diameter of the lens thread you are using. In my case, I ordered the filter for my normal lens that requires a 58 thread size. On the other two lenses, 63 filters would then be used.
In testing, I was thrilled with how easy it was to adjust and the quality of performance and workmanship is exemplary. Only, it would be nice if the setting had a min-max limit. So I had to always once briefly direct an eye on the lever, whether it is also in the adjustable range.
But this is complaining at a very high level. In any case, I am happy about this great filter and that the eternal change finally has an end.

Conclusion:
Very well made, variably adjustable ND filter (aperture 1.5 -10). Recommendation!

I hope that I could be of some help to you with my review. Thank you!

The filter is huge.
7.4mm thick and 159gr weight, designed probably more for outdoor use.
Multi coated surface (28 layers), filter made of glass, scratch resistant, waterproof,....

You get a shock when you hold it in your hand for the first time.
There is a scale in the front that shows the approximate values, all of this is easy to grip on the frame itself or adjustable with the small handle that is screwed on.

The filter rotates completely, i.e. at the end / ND1000 comes a tiny step before it goes up again. Because there is no stopper, you have to be quite precise to get the highest ND value.
Even though it is of course the common design of these filters, I don't find this particularly practical or easy to adjust. You really have to pay attention, the scale doesn't really help there because the highest effect comes after the ""1000ND"" entry. And a little bit of rotation further, the ND decreases again.

Optically everything is ok, I could not notice any major / disturbing color changes - at least nothing that one would not have expected with this type of filter.
With and without the filter, the image remains sharp.

The whole thing comes in a plastic bag, where the filter sits loosely inside, without any further cover - again, I'm rather the friend of the closable plastic covers, but ok.

For 80 euros you get a good tool at hand.
For me, not the optimum, but that is complaining at a high level.

The KF Concept gray filter is - as usual from other products of the brand - high quality processed and comes in a safe and practical case.

Thanks to the special coating of the Nano-X series, there is no unwanted light interference in the image during use. In addition, the resistance to scratches increases, which I can really confirm here. Especially when I'm out in nature, I often come into contact with dust, dirt or other obstacles, which so far have not been able to cause any damage to the filter.
Here, the excellent functioning dust and water resistance of the filter is also to be emphasized!

As expected, the imaging performance of the filter is very good. The aperture stops can be precisely adjusted and are a blessing for my 28-75 2.8 lens. This allows for longer exposures with the aperture open and great bokeh in bright daylight. In terms of image sharpness, I couldn't notice any differences in images with and without filters. Only color-wise, there is a slight distortion towards warmer hues. But that's nothing that can't be cleaned up in post edit.

The filter can also show its strengths in the video area. Thanks to the stepless change of the aperture steps, as well as the easy and smoothly operable adjustment mechanism, smooth and quiet aperture transitions can be realized here. Especially with older cameras, this is a great advantage!

For such a performance, every hobby photographer should also be willing to dig a little deeper into his pocket. With this filter, the price of currently around 80€ is definitely worth it! That the image does not remain unaltered is clear from the outset with such filters. Since these changes but here compared to competing products but really keep within limits and can be subsequently ""wegbearbeitet"", this is not a point of criticism for me.

Accordingly, full 5 stars and a clear buy recommendation on my part.

NEEWER has in my opinion once again brought a product on the market that makes you wonder - at least me!

The filter is delivered in a bag that is not quite practical in my opinion. Why not so practical? I'm more a fan of these hard cases, where the filter can be put inside. But is personal feeling, nevertheless, I did not want to let it go unmentioned.

The installation of the filter is kept very simple - filter out of the case, screw on and off you go. I use the filter on a Tamron 24-70mm 2.8f G2 and there this fits perfectly. No canting, or anything like that. What I've gotten used to: do not tighten the filter so much that you can not get it off later ;-) happened to me once, then never again *just saying*.

The filter quality I consider high quality and good. Well solved I find the rotary control to turn the ND filter in the desired position. A well thought out concept to not accidentally get your fingers on the glass.

For my purposes, as I use the ND filter, absolutely sufficient. The image quality is really great with filter in my estimation!

Price performance I find good and fair. I have had good experience with the filter!

The KF Concept gray filter is, as I have come to expect from the brand, very high quality workmanship. This is delivered safely packaged and comes in a beautiful and practical case.

Thanks to the special coating of the Nano-X series, it is ensured that no light interference is present here and it should also be more robust against scratches. Of course, there is still no absolute protection for it. The imaging performance is top and everything looks good even through the filter. The only negative is the representation of colors, because they are somewhat distorted by the filter.

However, the filter is not cheap in any case, but I am very satisfied with it all around.

I'm using the 52mm variant on a Sigma C 35mm/1.4 for Sony and consequently can only say something about it.

In brief:
(+) good sharpness and color fidelity
(+) good workmanship and feel
(+) improved adjustment by grip lever (no problem even in cold weather with gloves)
(+) stepless and versatile
(+) nice and practical leather bag for storage

The first question I had was how the sharpness and color fastness would be with the variable ND filter. Here I have made in the past with other products so bad experiences that I ended up using these filters only in extreme emergencies. You can achieve such beautiful results with ND filters. Wouldn't it be nice not to have to carry around 5 different filters and still get good results?

Besides the use in filming, the filter is for me especially for long exposures (eg at the water) and open-aperture shots in sunlight of interest.
In all three cases, the filter can be used well. The only thing you have to be aware of is that you can no longer use the lens hood due to the small handle lever.
The operation works so well with this lever that you can also use and change the ND-FIlter while filming. On the tripod one notices then also no shakiness.

The SHARPNESS is surprisingly good and also color changes / color casts / etc. I could not determine. Therefore, there is already a big plus here.

The ND value can be adjusted continuously. Thus, however, the actual value is not recognizable. There is a scale with small squares, which are in the right place even when the filter is screwed on - but this does not replace an exact indication. So if you want to be a hobby mathematician and calculate exactly how to adjust exposure time and aperture, you will have a hard time.
For me personally, however, this does not matter in practice. I simply take a few minutes more time and, in case of doubt, achieve the desired result by trial and error.
Particularly when filming, however, I can already see in the live view what the result will be and here the filter only serves to adjust the final exposure for me. It fulfills this purpose very well.

The workmanship is of high quality. The filter is not the lightest or thinnest, but seems very robust, goes easily but not too easily and especially the thread can be screwed on without the hooking and canting, which one has otherwise often with filters. The screwed handle element underlines the high-quality condition of the filter and supports the already pleasant feel once again in a special way.

I also find the stylish leather case successful. It is designed to be quite valuable and the filter can be taken out of the bag easily and without fumbling through a simple mechanism. to do this, you simply pull on a strap on the side, which runs through the bag and thereby pushes the filter upwards.

Conclusion:
Good filter that delivers surprisingly good results and is very pleasant to use.
The workmanship and quality leads to a very good price-performance ratio.

ND3-1000 is already a range. How accurate this is, however, I can not say specifically.

The build quality is very good and the small ""handle"" to turn I like. The FIlter is also quite heavy, so it can be adjusted well.

But what always bothers me with many variable filters is that there is often no stop at the min and max value. So also here.
As long as you move in the range of 3-1000 I could not find anything negative in the image quality. But if you go further than 1000, you see the infamous "X" on the lens. Within the normal range, however, I could not detect it.

I already have a variable ND filter, but I am not satisfied with it because the dial is stiff and the results do not meet my expectations.

Already sworn off ND filters I came across a product review for this K&F filter, which convinced me so much that I ordered this filter for my new lens (Tamron 35-150mm 2-2.8f).

Already with the packaging (high quality cardboard box with magnetic holder) and then the insert decorated with gold and then the leather bag for storage has gradually introduced me to a high class product. The filter was delivered dust free, has visible coatings and a really usable adjustment wheel to dynamically adjust the filter. The screw thread is flawless and the first results are much better than the tests with the rather simple filter.

I am satisfied, but expect this performance at such a high price. Highly recommended!

I already know other filters from K&F and was allowed to request this one for testing.
The packaging alone makes a good impression and when you open it, it continues with the case. That already makes something. But well, it is about the filter. The filter itself is a variable filter from ND3-1000, which is quite a range. I've never had a variable ND filter before and was skeptical at first if it would really work. But yes, it works.

The filter itself makes a high-quality impression. It can be screwed onto the filter thread of the lenses without any problems and can also be removed again. Adjusting the filter works wonderfully with the orange lever on the side. From the image quality I could not determine any losses.
The price is quite high, but for that the filter is also very well made.