The K&F concept variable ND is the perfect, lightweight filter for my ZV-E1 vlogging setup. It’s slim and light enough to not throw off my gimbal balance wether it’s on or off. It offer me a run and gun way of controlling my light without sacrificing my shutter speed and aperture. I like to stick to the basic rules of obtaining cinematic quality video, and this is one of the best ways to do it. There are way more expensive options out there that are endorsed by big name YouTubers, but they also come with a big price tag as well. To me, that marginal improvement is not worth the price. This filter is plenty good. Your colors will still be saturated, the corners will not suffer and you will not see any weird effects in your video, like cheaper brands will give you. This variable ND from K&F will stay on my lens when I’m outdoors.

I love the quality of this ND filter. It's built really well, east to install and works great. It comes in a nice case to keep it safe and the threading is very solid so it seeks it will last a long time. I recently used it to shoot on a very bright, sunny day for a work event at around 12pm so it saved my photos from being blown out.

In the past, I have only used ND filters with a fixed light reduction. While a fixed light reduction filter is far less complicated and, thus, less likely to add reduce image quality, you have to have several of them in varying strengths if you want to be able to use them in different lighting conditions and end up with the same camera settings. A variable ND filter allows you to adjust the light reduction without changing filters.

This one is machined very nicely and rotates smoothly. In my initial testing I didn't notice any image degradation. It does appear to add some warmth to the image but that is easily adjustable in photo editing. I have to do additional testing to see if the black X will be an issue. (The listing did point out that this variable ND filter can produce the black X when used at higher densities. There are more expensive variable ND filters that say they don't produce that affect.)

By nature of the way they work, a variable ND filter is larger in diameter than the lens it is attached to so the normal lens cap doesn't fit. This means you'll have to buy a larger diameter lens cap if you want to use one when this filter is mounted to your lens.

This is a versatile tool to add to my camera bag. I'll do some additional testing and, if I notice any issues, I'll update this review.

I found this to be a good filter at a reasonable price. I did note a mild, almost imperceptible color shift, a touch of vignetting, and a bit of softening at higher filter strength. None of these issue were show stoppers in my opinion and the filter was very suitable for stills. Most of those issues washed out in post processing so they didn't matter for me.

Typically when I need both a CPL and an ND filter that's two parts, this makes that one part and that makes my life easier in a lot of ways.

If you need a simple solution at a good price point this could work for you.

I don't use ND filters a lot, so I found the idea of a single screw-on filter that could substitute for several fixed ND filters to be appealing. I had read other reviews of this filter, with mixed opinions, so I did my own evaluation in which I was looking primarily at three things:
1. Color cast
2. Artifacts
3. Sharpness

I added the last one (sharpness) because of some comments another reviewer had made.

I tested the variable ND filter in a studio setting with the camera on a tripod and fixed settings for ISO, white balance, f/stop, and focus. I took images at 6 settings spaced across the range (MIN to MAX) and have included the images here.

Here's a summary of my opinion of the performance on these three criteria:
1. Color cast - GOOD. The color balance remained quite uniform over the majority of the range of the filter (see photo). The color cast took a giant step in hue (to blue) at the MAX setting. This would be entirely correctable in any image processing software, but in combination with the other considerations, I don't plan on operating close to the MAX setting.
2. Artifacts - VERY GOOD. I did not encounter any artifacts that resembled color clouds or the dreaded "x". However I didn't push it past its MAX setting, which is where some other reviewer encountered these problems. Didn't expect to use it outside its intended range so I didn't test it there.
3. Sharpness - OK. This was my biggest surprise. I wasn't even intending to check for this, but the degradation in sharpness and contrast over much of the range (with the exception of the lowest values of ND) was notable in the sequence of images I took. (See photo). It was serious enough that I'd be careful using this much higher than the 50% point between MIN and MAX. Perhaps this is just a by-product of using higher ND filters -- I don't know for sure. I don't have any high-end ND filters to compare.

The build quality and packaging are good. I particularly like the filter cases that K&F provides, they are easy to use.

CONCLUSION: This will be a useful filter for me, but because I know of the limitations and their effect on image quality, I can make some informed decisions about how where to operate this filter and what to expect. Post-processing will certainly improve the image quality and might be needed.

I now have 2 lenses with 82mm filter size that I use often for everyday and wide angle photography. So I need an ND filter for them. The K&F Concept 82mm Variable ND2-400 9 stop variable neutral density filter is pretty hefty. Nothing thin or lightweight on this variable ND filter. There is a triangular index marked on the fixed ring and dots on the rotating ring for min to max light reduction scale. Unfortunately, these markings fall at the bottom of my Nikon F mount 24-70mm f/2.8E lens, but it lands on the top on my Nikon Z mount 14-30mm f/4s lens. It would be useful to have this center at the top on both lenses to calibrate the light level changes.

With the 9x light reduction, this filter was even able to photograph the recent annular solar eclipse with 2 additional stops under exposure to see the partial ring of fire effect. But for other bright summer days, dialing to 4-6x reduction is mostly what I need for landscape photos. With a tripod and manual exposure settings or small f-stop on aperture priority, I can get the desired rich landscape scenes. Or with manual exposure or slow shutter speed on shutter priority, I can get the misty effects from waterfalls or flowing water ways or blur effects as cars or Ferris wheels in daylight.

I've not seen optical issues with this ND filter as I don't thread this over any UV/protective or polarizer filter already on the lens. I always put this ND filter directly onto the lens without anything in between that can cause adverse optical effects which is not the fault of this filter. I don't see any unusual lines, vignetting or aberrations or uneven lighting issues.

This is an economical variable ND filter that can cost 2-3 times more to get the less than 1-9 stops performance.

For the price, you get amazing quality seriously. The metal feels amazing and the turning action is so smooth, it’s a bit stiff but for precision it’s perfect

This K&F variable ND filter (ND2-400) is a nice budget choice filter that works good and won't break the bank. There are no hard stops on the adjustment ring and will spin either way endlessly. Other than that the filter is made well and comes in a nice case. Take note (as description states) that you will need a larger lens cap to put on the end of this filter if you plan to keep it on and want to add a lens cap. For instance I have the 72mm version of the filter and it requires need a 77mm lens cap. Yes they mention it but I think they should include the corresponding lens cap with the product based on the filter size purchased. You should also know that ND filters do not work like magic you have to understand all of your camera settings and the environment you are shooting in otherwise you may get poor results and blame it on the filter when it is actually just your settings that are wrong. It takes practice to get the proper settings for long exposure photography and every camera and lens combo will have different settings and results. I have always been happy with any K&F filter (and other products) I have purchased and this one is no different.

The build quality is pretty good. The rotation of the lens is smooth with a little resistance, which is helpful to more precisely set the ND level you want. The surface is clean and coating looks nice. There are clear marks on the dial to show the max and min levels. But the whole dial can rotate 360 with no hard stop. On the optical part, there is obvious pinkish tone on pictures but it can be easily corrected if you shot in raw. When rotating pass the marked range, you will run into big, dark middle and bright corners results, which are really unusable. But if you stay in the marked range, especially the lower section, the results are more consistent. Round ND's like this are more convenient and easy to use than the square ones. So I will take this filter to travel.

Son de buena calidad, pero si los pones al máximo nivel producen viñeta al igual que la X. Si lo usas hasta nivel 7 van perfecto. Entonces no son malos pero para tenerlo en cuenta.