Lenses of modern digital cameras are increasingly trimmed for sharpness and imaging performance, which is of course good on the one hand, but also brings with it a dilemma, namely that motifs often appear hard and rich in contrast and pictures somehow lack a certain charm. To soften this modern "look" a bit, to make motifs a little softer, highlights to be diffuse and a little softer, that's what effect filters like the Nano-K Black-Diffusion from K&F Concept are intended for and are particularly popular with cinegraphs . But photographers also benefit from such filters, as portraits, for example, get a pleasant, somewhat dreamy look without losing too much sharpness. The diffusion effect comes into its own when a light source, such as a window or lamp, is in the field of view. At first you will have to experiment a bit to find the optimal filter strength for the desired look. The K&F Nano-K Black Diffusion ¼ I tried is, in my opinion, ideally suited for gaining initial experience, since the diffusion effect is already very effective thanks to the filter strength of ¼, but there is still sufficient sharpness and contrast . In terms of both feel and quality, there is nothing wrong with the K&F Black Diffusion. The filter is very well made and has a flat profile to avoid vignetting. The thread is cleanly worked and smooth-running. I didn't notice any noticeable color shifts or vignetting. Tip: I always buy filters according to the largest lens diameter in my inventory and fit the filter via step-up rings, on the respective lenses on which I want to use the filter. This has the advantage that you only have to buy filters once and even if large filters are of course a bit more expensive than small ones, it is worth it in the end because step-up rings do not cost much. It may also be worth buying a complete set of such adapter rings with different diameters.