This K&F Black Diffusion filter is an excellent piece of kit. It reduces contrast, making the blacks slightly greyer, and provides a soft bloom around the highlights. There are four strengths of filter available; from weakest to strongest, they are 1/8, 1/4, 1/2, and 1. This 1/8 filter is the weakest but it still makes a noticeable difference to the look of the images that you shoot with it.

I was able to test this side-by-side with a Tiffen Black Pro Mist filter, and the results of each filter are extremely similar to the point where I can't really see any difference in the image, and I certainly couldn't say that either one is better than the other. Both frames are made of an aluminum alloy, and I feel that any aluminum frame can benefit from a little grease, even if it's just grease from the skin of your fingers that you rub over the threads. More expensive filters have brass frames which tend to be a lot smoother and don't stick. The K&F filter has about 1.25" of deep machined grooves on each side of the filter, which provide excellent grip for your fingers to hold when screwing/unscrewing the filter.

One aspect in which K&F is the clear winner is that the K&F filter case is far superior to the Tiffen case; the Tiffen case is a square case in which the filter sits loose on a piece of styrofoam, whereas the K&F case is superbly designed to hold the filter very securely in place with a clever system of rubber grooves that can accommodate different filter sizes.

This does have a filter thread on the front so you can stack another 77mm filter on top of it.

Overall I find this to be an excellent quality filter that is pretty much on par with the quality of Tiffen filters. It's a useful tool to have in a camera kit and is worth investing in.