The important thing with filters is that they don't degrade image quality, and also that they have no colour cast or flaring on final images.

As a pro photographer these are more important for me than most, and luckily these work perfectly.

He likes it as he has just started learning photography as I am his teacher.

I think that this is another great offering from K&F Concept, the filter is blemish free and fits perfectly on the lens, with the thread making it a quick process to put on and remove if required. I have bought several Lee and Cokin filters in the past and this seems to offer just as good service as the more expensive brands

Great service nice product

Have 4 of these in 77mm, 67mm & 86mm. For the price, they're good, have no noticeable image quality issues, easy to wipe the water off of. They do scratch fairly easy so depending on your usage you may need to replace them yearly, and when used without a lens hood in sunlight or directly into the sunlight you get blue ghosting (could be worse, but I remove it when shooting towards the sun).
But quality vs cost, these are definitely the best option.

I had used a popular UV filter before. It's not bad. Only under certain conditions would there be glare or aberration. For the most part, it worked fine. But it still bugged me. So I ordered this K&F UV filter. WOW! What a difference! The glass is SO clear you can't tell it's in the housing! And that is how clear my photos became with it on! Definitely worth the price difference! All my filters are now K&F brand. The quality is outstanding!

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.

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 am usually against UV/haze filters as I am concerned about their effect on image quality. However, I plan to use my Sigma 150-600 DG DN Sport (Sony E-Mount) in pretty harsh conditions such as coastal bird photography, surf photography, and sports. So, I caved and purchased this filter to provide protection for the lens front element.
However, given that this K&F filter would probably be considered "mid-tier" in terms of price, I wanted to test if it in fact had any effect on image quality. The attached image of a $20 dollar bill was taken under the same exact circumstances - 600mm at ISO 100, tripod with OS off. As you can see from the screenshot taken in the compare view of my photo editing software, the image on the right (with filter) is clearly sharper with better contrast.
I'm shocked! I had fully expected to remove the filter when I wanted a better image. Now I can leave it on 100% of the time, and easily wipe off any splashes or dust without worrying about scratching the front element. Strong recommend!

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.