KV37 43mm Fader Variable Adjustable ND Filter ND2-ND400 - Ultra-Slim & Multi-Coated Nano-Klear

The filter is thick but it is also larger than 67mm so the effective area is less affected by the thickness. I used Fuji 18-135mm lens to test this filter. When I set the focal length to 18mm (27mm Full frame equivalent) , I did not notice any vignette caused by this filter. Another test I did was set fixed aperture and shutter speed. Only thing that would vary was ISO. I then turned the filter to each ND level on the mark. I could clearly see the ISO keep moving up as the ND index went higher. When I compared the JPG results, I notched not much difference among those shots in term of brightness, color, or sharpness. So I would say that the filter is consistent within its intended stops. With these results, I would give this filter a go. With such a small package for 10 stops of ND, I definitely will throw it into my bag in travel.

Love it. Easy to use. Points must be used for correct alignment. Moving to the Min/Max mark creates the "X" you see in some photos. This is pure user error. I've done it myself. What I love about the variable filter is that I can set this filter to the lowest setting on my lens, set up and focus my shot, and then crank it to the maximum setting to capture my shot. The filter does not need to be removed to set up a different composition.

Photo: Nikon D7100/ Sigma 18-250mm
Iso 100
Shutter 1/6 sec
. f/4.5 (I think)
Nd - highest setting

Was rushing to take this shot as I was being eaten alive by black flies. So I screwed up my aperture and cranked up my shutter instead to get an acceptable exposure. I also had some condensation on my lens when I unscrewed the filter so there is a haze to the top of the image. Should have used f/11+ and a 1 second exposure but the water still mixed well.

I'm becoming a fan of K&F Concept lens filters. This is my third filter from them and so far I've been extremely impressed with the glass.

CONSTRUCTION
The filter attaches to my lens smoothly and comes off without binding. The frame is machined very well with a semi-rough coating that makes for a secure and confident grip on the filter while adjusting it. Adjustment is very smooth with quite a bit of resistance and won't change if you happen to brush up against it. You can gauge the VND effect with markings on the edge that range from "MIN" to "MAX" with a series of square dots that gradually increase in height.

VND filters tend to be thicker and can cause vignetting with shorter focal lengths. K&F's solution to this is to make the filter slightly larger than the lens diameter. This works great to prevent vignetting but it means that you can't use your existing lens cap. Using a lens hood is theoretically possible but the larger size means it'll be very difficult to set up even if it fits.

I have another K&F filter set that came with really nice machined caps. With the larger front ring diameter that doesn't fit your lens cap that would have been a great add.

TESTING

This filter is specified to produce 1.5 to 10 stops of light reduction. I measured approximately 1 1/3 to 12 stops of light reduction with no visual artifacts such as the dreaded "X" effect you get with some VND filters. The filter imparted a slight warm cast (~300K) that remained consistent throughout the range getting slightly warmer only at maximum.

K&F state that the filter markings are not calibrated. I measured the effect under relatively controlled conditions and found that the VND effect isn't linear but instead starts off slowly but increases much faster as you approach max. Because of this adjustments at higher strengths can be quite tricky.

I would have really appreciated calibrated markings to make adjustment easier, but since it doesn't have this feature I measured the approximate strength and made a chart.

MIN
Solid 1-4 = 1 1/3, 5-6 = 1 2/3, 7-8 = 2, 9-10 = 3, 11 = 4
Hollow 1 = 5, 2 = 7, 3 = 12
MAX

You can ignore the Min and Max markings since they don't produce any meaningful changes.

SUMMARY

With this filter you're getting great neutral glass that's comparable to much higher-end products at a much lower price point. Even with minor negatives it's a fantastic all around value. Highly recommended.

PROS
Minimal color cast (+300K)
Adjustable from ND3 to ND1000 (1.5 to 10 stops)
Multilayer coatings for glare reduction, resistance to skin oils and easy cleaning
Does not vignette
Graduated markings from 'min to max'
Threaded front ring

CONS
Filter is larger than the lens diameter
You can't use your lens cap or lens hood
Markings are not calibrated
VND effect is decidedly non-linear and tricky to adjust at higher strengths

After I needed a new gray filter for my DSLR, I decided on this model and was not disappointed. I am an amateur photographer. Pros may have different needs, but I wasn't disappointed.

That thing is ridiculous! Received it yesterday and took it out today for some waterfall pictures in a small creek nearby. That was around 5 o'clock in the afternoon. Nice bright sunny day. I was able to shoot 20 second shots with no problem and could have done longer. I got some nasty flares on some of my images but I think that was my problem as I was shooting towards the sun and it's not on all of my images. I'll have to try again and take a picture with the sun behind me and see how it works. But for the price, there's no reason not to have one for each of your lenses. Very happy with it. And it is beautifully made of metal and screws in smoothly.

My wife and I are picked up a couple electric scooters and I thought it would be good to mount our GoPro and get some video, so filters are very nice accessory that can make a big difference. This filter is just amazing well made, such high quality and beyond. Perfect all the way around. Screws on to my camera enclosure perfectly. Filter adjusts very smoothly and it's surprising how wide a range it has. i am no photography expert, so sure it will take me some practice to get it down.

Filter comes in a nice plastic case to protect it. I only wish it came with some kind of lens cover to protect the lens when it's out of the case. I can just take it off each time, but would be nice to leave it on.

Very nice filter, price is good, gladly recommend.

long exposure. At first I hardly used it, now I'm a big fan. I looked around and found the perfect tripod (carbon fiber Manfrotto, great too). When that caught on, I mentioned to my friend that I was planning on getting waterfalls with a slow shutter speed and he said, "You need an ND filter, don't you?" I knew there was a trip to Letchworth coming up this weekend. That evening I went to Amazon, made a purchase and found this product. Perfect size for my Zeiss 50mm and 35mm!

Didn't really get a chance to play around with this ND filter until I got to Letchworth and wow I was blown away! The crisp rolling ring and crisp black tone make this such an incredible product. So worth the price! I'm blown away by how it doesn't affect the quality of my shots that my lenses can achieve.

Now I love long exposures. With my light tripod and my filter I can only grow.

I've attached an image of a covered bridge in Cuyahoga Valley National Park taken with this filter. It was an eight second shutter speed.

This is my first variable ND filter and Im very happy with it. I got the 67mm version because its a very common size and I already have three lenses that it could fit. Plus with adapters, I can get my smaller lenses to work as well.
The filter. Overall its great. Metal construction with a very smooth ring.
The stops are marked on the ring and the overall construction is very good.
Again this is my first variable ND and so far I'm enjoying it very much.
Price is affordable too.

I almost gave up investing in an ND filter because I wasn't willing to shell out $200 or more for a few waterfall shots. Stumbled upon this one and loved it. I took it with me on my trip to Italy and it gave some phenomenal shots in full daylight. It worked great both with 30 second exposures of waterfalls and when I just needed it to block out the haze of the rising sun on the top of St. Peter's Basilica. Sure, there may be a shadow around the edges, but the overall quality of photos this offers is worth it.

I bought the K&F Concept ND filter for my Sony Alpha 7 III. I use the 67mm version.
The filter arrived the third day. Everything was well packed and undamaged.

The processing is really impressive. Very clean glass and no scratches or anything like that.
The intensity of the ND filter can be continuously adjusted from ND2 to ND400.
I took a few test photos with the filter and am absolutely satisfied.
The only drawback for which there is a star deduction: At the maximum filter level you have a bluish shimmering X in the photo. This is a bit annoying, but if you turn the intensity down to just below the MAX level, it disappears again.

All in all, you can't go wrong with the ND filter from K&F Concept. At a reasonable price you get a universal ND filter. I give it a clear buy recommendation and because of one shortcoming 4 stars.
I hope I could help :-)