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.

Great clarity and protection for my lensp

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 took a beach vacation recently and wanted to protect one of my favorite primes from salty air and sand. The results were flawless, I didn’t find any chromatic aberration or fringing. The metal threading is a real plus which provides a secure fitment for peace of mind.

Use it as a protective filter, no noticable degradation on the sigma 150-600 FE.

Protection for P900 lens

Added protection for my new camera.

works good fits good price good would buy again

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

Used for Sony A7c camera