UV filters are perhaps the most popular type of lens filter, with many photographers using them to protect the front element of an expensive lens. Unfortunately, there’s a huge range in the quality of UV filters out there. I wanted to put together a methodology to test UV filters, and other filters, more precisely. Today, I’ll be performing those tests on the K&F Concept Nano-X 67mm UV filter.
Table of Contents
Intro to the K&F Concept Nano-X UV Filter
The K&F Concept Nano-X UV filter is a thin UV filter that has some sort of 28-layer “titanium coating” feature that is supposed to reduce flare and maintain sharpness. When I was testing it, I certainly didn’t notice any loss of sharpness with my unaided eye.
This filter comes in a nice case with a non-slip rubber holder inside. This design also fits smaller filters securely, and the rubber holder prevents the filter from rattling around and scaring rare owls. That will come in handy if I ever find a rare owl.
Color Accuracy
The first and most noticeable problem with some filters is a warming or cooling effect. I test this using a relatively constant light source on a Calibrite Color Passport target, checking the white balance settings with and without the filter in multiple trials. From these trials, a 95% confidence interval can be generated for temperature and tint modification:
The way to interpret these graphs is this: the color temperature change was just on the edge of statistically significant, and the average change was a cooling effect of about 24 Kelvin. Basically in the real world, you will not notice much of a change, and any slight change will be easily correctable. Not bad! As for the tint, the change was effectively zero.
But we have to dig a little deeper. Even if a filter changes the white balance a little, correcting it can still result in color inaccuracy in the individual color channels, even if white tones are corrected back to white. (This is especially prevalent in JPEGs, but can also be visible in raw files if it is significant enough.)
So, for the next color accuracy test, I measured the distortion of RGB and CMY colors in degrees on an HSL scale, as well as on two skin tone axes. This test is slightly affected by the lens used. In this case, I tested it with the Nikon 50mm f/1.4 Z, a lens which I’ve found to have minimal color inaccuracies.
Again, these bars represent the 95% confidence interval of the difference between the bare lens and the filter. It’s good if the bars contain zero, bad otherwise, and the strength of the effect is represented by the numbers. The units are in degrees, and typically if the effect is less than 0.5, it will be unnoticeable.
Since all the bars contain zero, with very small effects besides, this filter is pretty much perfect for color preservation. Even the distortion in the first skin tone is well below the threshold of being a problem photographically.
Flare and Contrast
All filters interfere with the light coming into the lens, and it’s just a question of how much.
Unfortunately, it’s very difficult to come up with a measurement of flare that is comparable and meaningful in all situations. That’s because each lighting situation will be different, and each lens also is prone to different sorts of flare that can be even more exacerbated by the filter. Nevertheless, I can say that in a variety of situations, I found the flare to be well-controlled with this filter. In a worst-case scenario test, with the lens already flaring, I compared the before and after contrast reduction once the filter was added. Here are side-by-side images showing the visual difference:
It’s not too noticeable, but there is a slight effect if you look closely in the bottom right corner, which is where the light source was coming from. And here is the corresponding confidence interval of the difference between the lightest bottom square and the darkest:
So, there was a meaningful loss of contrast with a small effect of about 3.2 luminosity units in the HSL scale. Therefore, in the worst of situations, such as slightly off-axis light like sunlight blasting into your lens, taking off the filter will likely improve your contrast a little.
Finally, I did measure the vignetting, which was nonexistent at 50mm, although I did not have wider focal lengths to measure.
Conclusion
Overall, the K&F Concept Nano-X UV filter performed well in my tests. It has excellent color accuracy, no meaningful loss in image quality, and only a slight reduction in contrast in more severe backlit circumstances. It’s also a well-made and durable filter that comes in a nice case. Especially considering the low price, this is an easy filter to recommend. (Prices range from $32 to $53 depending on the size that you select.)
If you’re interested in this filter, consider buying it through one of our affiliate links support the rigorous testing that we do at Photography Life! And be sure to select the correct filter size to match your lens:
My biggest problem with this filter is that it’s backordered at most sizes. If you don’t want to wait for yours to arrive, you may want to check Amazon or Adorama to see if they have the size you need in stock:
I hope that you enjoyed this review! I’m looking forward to testing more filters soon, including with some new testing methodologies that I’m developing. What about you? Do you want to see more filter reviews or scientific comparisons like this one? Feel free to let me know what else you’d like me to test!
I never invested in this item, which is useless to me as long as the lens hood is permanently mounted on the lens. I’ve never had any breakages and I prefer to have one element less.
When I was a newbie I was told that Vivitar series 1 uv filters were the best. I didn’t know any better back then. When I eventually changed them out, I went with a brand that B&H sells called Chiaro, which comes in several series ranging from inexpensive to very expensive. They have differing characteristics, and you get to choose what you want in a uv filter. I use the T98 series, which are not cheap but don’t break the bank. I’ve never noticed any issues with them. I don’t think that they impair my photos in any way. Since you are planning to test many types of filters, I suggest that you test one or more of the Chiaro line.
Would love to see a comparison with the NiSi AIR UV’s, it’s a claimed 99,6% transmitance vs 99.9%. I’ve been using the NiSi’s with a Nikon Z8 and a Z 180-600mm and I can’t find any loss of detail while using the filter, even searching at 200%. Did you test for “sharpness” with the K&F UV filter? These X-series are quite good, and for a stupid low price.
If there’s interest, I should be able to test filters for sharpness in our usual lens-testing lab while Jason runs other tests on them! My expectation is that most modern filters won’t lose significant sharpness, but I’d be interested to see analytically.
The biggest problem I’ve had with filters (including K&F) is the phenomenon where the cheaper ones get stuck to each other or step up and rings (I’ve read this is a metal thread contact problem, especially with aluminum). Usually time in the freezer and a wrench solves it but it’s a pain. I’ve never had this problem with B+W. So optically I think many filters are equivalent but there is something to be said about build too.
Good point. I don’t typically stack filters or use step-up rings, but your information leads me to believe that more rigorous physical tests would be useful in the future! I will see if I can incorporate some.
Yeah aluminium threads suck, the metal is to soft it might get stuck if you apply enough pressure. Top shelve filters use brassm which is more expensive, but much more durable.
Yeah, it’s worse when the filter spins. I got a K&F variable ND for shooting video and it got stuck on my step up ring. What really sucked is that I didn’t apply a lot of pressure to put it on the ring, but spinning it to adjust the ND strength got it stuck. That was a challenge to get off, to put it mildly.