I recently picked up the K&F Concept 2-in-1 82mm Black Diffusion 1/4 & Circular Polarizing filter, and overall, I’m really happy with it. The materials are top-notch—both the metal frame and the glass feel very high quality, which is reassuring for regular use.

In terms of light reduction, it cuts about 1.1 stops of light based on measurements I took using a professional light meter. While it wasn’t a lab test, I measured it in a fairly controlled environment, so that’s something to keep in mind if you're concerned about exposure adjustments.

One thing that surprised me is that the filter isn’t as color-neutral as I had hoped. Using a professional spectrometer (colorimeter), I noticed it introduces a slight green cast. This is especially worth noting if you're shooting under lighting that already has a green tint (like certain nonprofessional fluorescent lights). It’s not a dealbreaker since color shifts like this are easily fixable in post-production, as long as you're aware of it and know how to compensate.

As for the Black Diffusion 1/4 effect, it’s exactly what I expected. It adds a nice soft glow to the highlights without messing with overall clarity or sharpness. There’s no weird texture or unintended effect, which is great. The filter keeps the image quality under control while still giving that subtle misty effect.

One of the best things about this filter is the space it saves in my camera bag. Having both the diffusion and polarizing effects in one filter means I don’t need to stack multiple filters, which can lead to vignetting on wider lenses. It’s a smart and practical 2-in-1 solution.

It also comes with a very nice protective case, plus a couple of cleaning tissues, which is a nice bonus to help keep it in top condition.

Despite the slight green cast, I think this is a very good filter. It’s a smart space-saving solution, and the Black Diffusion effect is subtle and well-executed. Just be mindful of the color shift, and you’ll be set!