This filter is really good quality, both the glass and the general manufacturing. I got the 82 mm filter, and had no problems screwing it in. The fixed piece is a few millimeters thick, so it’s easy to grip and has some textured areas that make it easy to screw onto the lens without spinning the moving part.

The outer rotating filter works extremely well. It’s easy to move, but definitely holds in place well, unlike some other variable filters I’ve had in the past.

My favorite feature is that the ND values are marked on the filter at 2, 4, 8, 16, and 32 stops. It’s variable in between those, but super easy to hit a starting point if you know approximately how many stops of light you’re trying to offset.

The K&F Concept filter is a solid build, with some really good features that you don’t see on every variable neutral density filter. It’s a thoughtful design that’s well-executed.

My first impression was...for the money...it's not half bad.
But that impression slowly evolved...
Build is very nice...plenty of grip. But in attaining a nice grip, you get a fat frame.
I went with the 82mm filter to place on my Sony 135mm f/1.8...probably the best lens I have.
I could not put the lens hood on with the filter attached. I have a Polar Pro and I can have the hood attached. Deal breaker? No, but I like to have options whenever I can...so that's a ding.

It comes close to the Polar Pro in color cast...almost. There is some there but for the money...quite acceptable.

What is not acceptable (to me) is the loss of sharpness. It's definitely taking a hit...if you look.
My 135mm is razor sharp...to a fault. I shot this K&F against my Polar Pro for sharpness.

The Polar Pro looked just as sharp as shooting without any ND filter on...and sort of what you pay for.
The K&F reduced the sharpness...in focus mag...I was never happy with what I saw...you think it's almost there...and you go past it (the sweet spot). You go past it because it is NOT there.

I would pass on this filter. If you need something razor sharp in the image with blur around it (typical usage of an ND).

The color cast part was very good...almost gone.

But the overall softness in the filter...is a no go...for me.

K&F Concept is a brand that slowly crept up on me and now I seek out their stuff for a good quality alternative to the expensive name brands. Their stuff is typically made high quality at a price that won't break the bank. This is no different. Filter is great quality and I enjoy using it for some unique daytime shots that I couldn't get without it.

I’ve been a fan of K&F Filters for some time now, and have come to appreciate the consistency and the quality of the brand. The majority of my lenses live their lives with K&F UV protective filters on their front element.

Like many others, as the caliber of mobile phone imagery and videography have improved to levels of near professional quality, I’ve begun to concentrate more energy into taking advantage of those attributes, not to mention the portability.

In hand, the K&F Concepts Variable ND2-32 filter does give the impression of quality. In fact, I own the same K&F variable ND filter in a larger size, 67mm. All modern quality optical glass is coated to reduce reflections with K&F following that convention; the 24 multi-layers of anti-reflection coating the seller asserts are appealing and evident to behold.

A variable ND filter works in a similar manner to a CPL, that is, there are two-rings, one that attaches it to a lens and the other that is turned to control the degree of transmission from more or less light, effectively allowing control of exposure. With that in mind, the K&F filter has a comfortable amount of thickness along with knurled edges on one of the rings that allows for ‘sure-footed,’ precise control while being rotated. K&F has not skimped on material or fabrication.

A ND filter, whether variable or not, is used to reduce the amount of light reaching a light sensitive material. In videography, it is generally to follow the convention of a low ISO and a low shutter speed. In still photography, to allow for the use of a wider aperture in bright light situations. In either case, the benefit of the K&F Concepts variable ND filter is that the transitions between minimum and maximum light reduction are not stepped, but infinitely variable between its 2 - 5 stop range. In other words, one can set their camera to the desired settings, then rotate the light reducing transition ring to achieve the desired exposure. Also, adding a second, fixed ND filter to the lens, for example an ND8, effectively increases the K&F variable ND from its 2 – 5 stop range, to 6 – 10 stops, a range of needed light reduction not uncommon when shooting video in bright sunlight.

There are two conventions for stating the amount of ND a filter provides, Optical Density Number, stated in thirds, with each third being a stop of density, for example .3, .6., .9, etc would be 1, 2 and 3 stops. The other is Filter Factor, the convention used by K&F. The Filter Factor rating is based on the actual amount of light reduction between stops, and is related to the inverse square law of light transmittance. Simply put, for each doubling of the FF number, there is a reduction of one stop of light. So, in the case of the K&F Concept ND2 – 32, you have 0 – 2 = 1 stop, 2 – 4 = 2 stops, 4 – 8 = 3 stops, 8 – 16 = 4 stops and 16 – 32 = 5 stops. And so on.

The K&F Concept Variable ND2 - 32 Filter comes from a trusted manufacturer, is high quality in both fabrication and materials, and serves very well the need for which it's designed. That is, by facilitating the means by which the standard video convention of keeping shutter speed and ISO low, can be followed. It does this by precisely reducing the amount of light in brightly lit scenarios. In other words, it allows some control over otherwise uncontrollable circumstances.

ND Filters come in many shapes and sizes. Some in square shapes that you can slide into a filter holder.
I prefer the round filters for easy screw-on. All you have to do is rotate for brightness or darkness. This one is great for just that.

I have little experience with ND Filters and though this is only 1-5 stops it is a great start.
Additionally, it gives me far more options to shoot in bright sunlight.
The anti-scratch means I don't have to worry about damaging the filter while experimenting.

I haven't pixel peeped, but I see no degradation in images taken with this filter. Range of the neutral density filter is ND2-32. Exposure is consistent throughout the frame; I see no vignetting or artifacts caused by the filer. The filter itself appears to be well made; dots are on the side of its outer ring noting the different ND levels, but I felt no clicking or notches. It is easy to use, especially with a mirrorless camera.

I’m a better photographer when using this ND filter as I can take advantage of camera features that normally would not function in bright light

So, the ND filter itself seems good quality. I got this for my old 35mm film camera and my vintage lenses which have a lot of 49mm outer threads, but looks like I’ll be looking elsewhere.
I have other K&F filters which I like and work well, but I can’t for the life of me understand why they would design this one like this.
Maybe this is specific to the 49mm filter since it’s a smaller diameter, but on this version the outer threads on the filter are larger than 49mm, meaning that the lens cap designed for a lens with… say… a 49mm filter…. Doesn’t fit. So if you want to use it you’ll have to find another lens cap (what size? Maybe 52? Trial and error because it isn’t marked on the filter!) or constantly be taking it on and off while walking around, which makes it effectively useless.
Simple solution? INCLUDE A LENS CAP THAT IS THE CORRECT SIZE, K&F! I have other VND filters for my larger lenses that are designed like this but they came with the appropriately sized cap.

In terms of build quality, this is a pretty good filter. The threads are good for a budget filter and do not bind easily. The adjustment ring is a little stiff but still pretty easy to maneuver. There are also hard stops at the beginning and end of the filter's range to prevent you from over-rotating.

Unfortunately, this is another poor showing from K&F in the area of optics. To the filter's credit, there is almost no color shift and no vignetting or x-pattern within its functional range. However, there is a major loss in sharpness that, in my testing, is the worst at the middle of the filter's range and improves slightly at the beginning and end of the range.

You could film with this filter if you had to, and you would get OK results as long as you don't crop your footage at all, but clarity and overall image quality are going to fall off quickly if you do try to crop in. I would only use this filter as a last resort, and my personal recommendation would be to spend a little more money to get a Freewell VND for around $100 that in my testing has virtually no loss in sharpness or clarity.

The image attached to this review shows a 100% zoom where the photo on the left was taken with no filter and the photo on the right was taken with the K&F VND at approximately the middle of its range.

This ND2-32 filter has a neat trick; instead of endlessly turning the filter round and round, trying to find the correct density, the movable frame of this filter has a notched stop! The filter markings are only painted dots, rather than setting numbers, but it is easy to figure out that the base setting is ND2, with dots at ND4, ND8, ND16 and ND32. Performance is great, too – the green-tinted filter cuts IR and UV, providing a neutral light transmission for improved color values and the multi-coated filter glass is distortion-free. At 67mm, the filter is noticeably heavier than others I have used, but it is robustly built. For photography work in the ranges this filter provides, it is most definitely the one I keep ready-to-hand in my kit!