XN21 52mm ND8 (3 Stop) ND Lens Filter HD Fixed Neutral Density Filter, Ultra Slim Frame Import Optical Glass Nano-X Series for Camera Lens

The lens filter looks good. Fits well on my nikon 50mm f1.4 ais lens.

As a photographer, I try really hard to make sure I’m only using gear that is reliable. K&F has done a great job of being a reliable company for budget-friendly camera gear. I have some of their other pieces of equipment and I continue to be impressed by both their dedication to superior build quality and attention to detail in their products. I found that the filter screwed right onto my lens without any issues and I was also able to remove it without any problems. Unfortunately, I wasn't able to capture a long-exposure because I don't live near any waterfalls and at the time when I got this filter, the weather really wasn't cooperating with me much. I did, however, hold the filter up to the lens without screwing it onto the lens so that I could see the difference between the image with the filter and without. With this type of test, you can clearly see a correctly exposed image and one that is darkened quite a bit with showing only the ‘hot’ spots of light in the photo. I did take a few shots with the filter installed and I noticed that there was no edge vignetting issues and because the glass is high-quality, I didn’t notice any ghosting either. All in all, this is a really nice option for a budget-friendly ND lens filter.

Got this to reduce overexposure with the Canon 17-40 4L wide lens. Pretty happy with the results so far, and it is definitely great for long-exposure shots. I have been K&F lens filters for a few years now, and they have been my primary ND filters.

Decent fixed nd filter

The K&F Concept filter arrived in a round protective case that seems to be universal as it'll fit many sizes of filters.
The filter itself is visually high quality and has knurled grips placed on opposite sides of the filter to provide good grip. The filter is very lightweight due to the aluminum frame construction and thin glass. The filter is very low profile to minimize vignetting but still has threads for stacking other filters.

The aluminum frame is also this filter's greatest weakness. Unlike my other ND filters with brass frames which attach and detach easily, the lens threading on the K&F seems to be so far out of spec that it grinds and binds terribly when trying to attach it to a lens. I was able to partially thread this onto the lens so I could test it out but never did fully attach it as I was afraid I'd damage the lens.

In terms of optical performance it reduces the light by the specified three stops (a 1/8 reduction). The MRC coating on the filter cleans easily and I didn't see any significant evidence of glare so the coating is doing its job in that regard. Many of these types of filters impart a color cast depending on the materials and coatings used - for example B&W's Schott glass is well known for imparting a yellowish cast. The K&F filter is very neutral in that regard - while it does impart a bluish-green tone to the image it's so slight that it's nearly unnoticeable. The most neutral filter I own is a Breakthrough Photography X4 ND filter, and this one is very nearly as good at 1/6 the price tag.

I really wanted to like this filter. It has decent optical performance, and it's low profile enough that it's useful as a stacking filter. Unfortunately, the threads on my sample make the filter practically useless which isn't good at any price.

I would rate this filter 5 stars for the optics and 4 stars overall if the filter threads were OK. Other than the threads I think this filter performs well enough optically that if you get a good sample it's a fantastic bargain.