I always get filters w/ non-slip design when it's available. It makes a huge difference. I compared it w/ Hoya HD2. I shot these w/ Canon M50 w/ Nikon 35-70mm f/2.8 AF ZOOM-NIKKOR.
1) No filter. 2) K&F. 3) Hoya HD2.
Sure, it's not a great test but I can't tell any difference between all 3 of them. The Hoya was optically as good as K&F except it was very staticky that I had to return it. I didn't like it's not non-slip either. The K&F is not staticky at all and very easy to clean. When there's no reflection, it looks like there's no glass inside the ring. Kind of like magic. It's very well made.
I use it on my Zeiss 50mm f/1.5 Sonnar T* ZM. There's no play and it fits perfectly. Very happy about the purchase.

This filter just helps keep the gunk off the front element. This protection helps keep the lens from slowly getting micro scratches and ruining the whole lens. Easier to replace a filter then a lens.

Just got a new lens, needed a 77mm filter to protect it. I'm not going to sit and tell you this glass is better than some other glass. I just got it, and I'm not an optics expert.
But, I will tell you the packaging was beautiful, the filter case- one of the nicest I've ever seen. It is circular- and holds multiple size filters with grooves in an internal bracket. So much nicer than the big clunky square filter boxes I've got from other brands.
But- the killer was the filter being so thin- and that it has 2 areas that are gnarled, for you to grab it- while the rest is smooth- a really nice feature.
Seems right at home on my Canon RF24-105/4 L IS USM.
Didn't notice any difference in speed of focus- or aberration- but, again- I'm not a lab.
I'm pretty happy with this brand. Didn't expect to be.

I bought this filter with no knowledge of the company. I still don't know anything but what I have observed: it seems to be quality construction and, most importantly, I took it out shooting and the clarity and visual performance of my favorite Nikon wide angle lens remains just as superb as ever. So, it's a quality filter at a very good price.

I first purchased the K&F Nano Series filter for one of my lenses. I believe it was for my Nikon 80-200mm F2.8 D ED lens. That lens produces really sharp images at distance and is not a close focus lens, even noted by Nikon. I bought the lens used and it came with a beat up UV filter. I was getting ghosting and when I removed the filter the ghosting was significantly reduced. I ended up buying several more for my other lenses. I also use B+W filters too. Well made filters as well, but a little more costly. The K&F is by no means a $100 filter, but for the price it does what I need. I especially like the nano-coating that resists grease and water. Worked well when I was photographing at the beach. Easy to clean the sea mist off without smearing.
We really do not need UV filters anymore with digital since UV does not interfere with the sensor like it did with film. I simply use them to keep from having to clean the front elements of my lenses all the time. I feel reducing that to a minimum will prevent potentially scratching the element. I know there are a few schools of thought on this topic, but I just do what I am comfortable with. From what I read and can tell the filter is glass and not plastic, which is nice these days. I have them on all my lenses now and happy with them.

The lens is so clear that when I opened the package, I thought they had mistakenly sent me just a ring. It took several attempts of rolling it around in the desk light to see that there was actually glass in there. And talk about CLEAR photos! No UV haze what-so-ever! No ghosting, no aberration. I wish K&F Concepts also made lens converters. I need this level of quality at this affordable price!

I purchased this for a camera that I seldom use. It still is a valuable collectors item that I want to keep in excellent condition and that means I needed to protect the lens. I only have filters with the Zeiss "T" coating constructed of German Schott glass on the cameras I use frequently, because I consider them the best multicoated filters that I can afford but, I cannot spend that kind of money for a camera I use infrequently.
Any camera that is threaded to accept a filter deserves the protection that comes with a mounted filter in front of the actual camera lens. I would rather risk damage to the AR coating on a filter that can be easily replaced than risk damaging the actual lens on any of my cameras from cleaning, and exposure to airborne dust or chemicals.
This brand of filter came carefully packed and the filter holder included with the filter is well designed and provides excellent protection for the filter when it is not on the camera lens because I am using a different type of filter. This filter has multiple AR coatings on both sides of the filter and after comparing the results of identical pictures with the same camera using this filter and one of my prized and now unaffordable Zeiss "T" filters I can say that I can see no difference in the results. I am sure an optical lab could document some differences, but in the real world, I can see no differences when comparing the test pictures I captured through this filter and the Zeiss filters I have used.
This design works so well, I will slowly replace the older non Zeiss filters I have on my older lenses and cameras with these newer designs.

Excellent filter for the price. I think every lens should have a polarizing filter, so bought this for my new lens. I can't tell you how nice the glass is....just buy it and see what you think. I don't think that you will be disappointed at this price-point!

Both lenses are Sigma lenses with 2 different brands of UV filters on them. The lens on the left is my 150-500mm with a filter made by another brand. The right is my 150-600mm lens with the K&F filter. The lens on the left looks a little hazy, while the K&F filter does not.

Does not decrease image quality that I can tell. You can feel that it is weather sealed, but I'm not testing it to see if it truly is.

Comes in a plastic case

So far, no complaints.

Finely machined. Nice to handle. just the right amout of friction turning the knurled ring. Good gradient on the polarizer, very distinct. Some loss of light but images are crisp. Good price for a nice, clean piece of glass. Very low profile. Fits my retractable lens camera with no interference. ( Panasonic DMC FZ 28 ).