This is a review of a 77mm K&F Concept Nano-K Series ND2-32.

First impressions are that this is a very well-made filter for the price. The body is machined from aluminum, with a matte anodized finish. The threaded rear ring is nicely knurled. The rotating ring has very fine knurling on the front edge. There are varying sized dots on the edge indicating the number of stops (1-5) of exposure reduction. Numbers would be a little nicer, but the dots are not hard to figure out.

The rotating front element is larger in diameter than the rear. This should minimize any vignetting with wide-angle lenses. However, if you expect to stack filters on top of this, be aware that the thread diameters are different. On the 77mm version, the diameter of the front threads is 82mm.

The filter threads into the lens smoothly with no signs of binding as you often see with inexpensive aluminum framed filters. Once mounted, the front ring rotates smoothly, with hard-stops at 1 and 5 stop positions. The total rotation from the minimum to maximum position is a bit less than ¼ turn.

The 1 to 5 stop range is good for bright conditions where you need a slower shutter speed to sync with fill flash, or a wider aperture to better separate the subject from the background. If you need super long exposures for super silky water effects, K&F makes a variable 2-9 stop version, as well as 16 and 20 stop fixed ND filters.

The stop marks on the filter rim appear to be pretty accurate. Using aperture-priority mode, the shutter speeds were very close to the expected progression. Starting at the 5-stop setting, the speeds were 1/8, 1/20, 1/40, 1/80 and 1/160. And removing the filter yielded a speed of 1/320.

Coloration is the downfall of many ND filters. Through a DSLR viewfinder, this filter seems to add a subtle greenish-yellow cast. Surprisingly, in my test images this coloration is visible only at the lower density settings. By the 3 stop mark, the color balance is quite neutral. Overall, not a bad performance.