I have always opted for the mountable type in the past for the sake of simplicity but the disadvantage of these is that you cannot stack filters without introducing heavy vignetting to the edges of the image. So when K&F Concept asked me if I'd like to review their Square Filter System and a couple of their Pro range filters, I thought it would be a great chance to see for myself what the pros and cons of this setup are.
The bundle I was supplied with includes the square filter system itself, an ND1000 Pro series filter and an ND8 graduated neutral density Pro series filter. The ND1000 is K&F's version of the classic Big Stopper style of filter pioneered by Lee and the ND8 grad is a classic design and must-have filter in pretty much any landscape photographers kit bag.
The filter system itself comes in two main parts - the adapter ring, which screws onto the front of the lens itself, and the filter holder which then clips onto the adapter ring. This kit is supplied with eight adapter rings (49/52/58/62/67/72/77/82) catering for most of the common lens thread sizes. I used the 77mm and 72mm on my 10-24mm and 100-400 respectively. The filters themselves are supplied in hard-wearing leather cases which are ideal for keeping the glass safely in a kit bag.
Once you've mounted the adapter to the lens, you can attach the filter holder. This easily clips onto the adapter using a convenient lever latch system. You can insert the filters into the holder while it's on the camera, but I found it much easier and more convenient to slot the filters in first and then clip them on. The filters are held in place using secure rubberised grooves - there's no way a filter will ever come loose once they're inserted as the grip of the holder is extremely firm. That being said, the filter holder has been designed specifically to rotate freely on the adapter ring so that you can correctly align graduated filters and circular polarisers.
I was impressed by the quality of both the filter holder and the filters themselves. The holder is made from black-sandblasted CNC-cut aviation aluminium which is both light and extremely rigid. I have no doubt at all that this will cope well with being chucked inside my camera bag and the wear-and-tear associated with sitting on the front of the camera in hostile environments such as at the coast.
The ND1000 filter supplied in this bundle is the sort of filter that every landscape photographer should own. It enables you to photograph long exposure shots even in full daylight, rather than having to wait for the reduced light at either end of the day. This offers a lot of flexibility and opens up a whole range of possibilities for cool shots.
I decided to put the ND1000 to the test by shooting in full daylight - in fact I shot not long after midday on a largely cloudless day when the the sun was completely unobscured. With the filter on my X-T4 with the 10-24mm lens I was able to shoot anywhere between 1 and 30 second exposures in full daylight. For the longer exposures I stopped the lens down to f/16 at ISO160 and this gave me exposure times of between 8 and 10 seconds which are ideal for shooting those milky-water shots where everything's smoothed out and splashes are reduced to haze. For the shorter exposures, I opened the aperture up to f/4 at ISO160 and this game me exposure times of between 0.5 and 1.5seconds. These sorts of exposure times are ideal for capturing waves mid-splash.
10-stop filters like K&F Concept's ND1000 started out life as something of a niche product, but they have become much more popular over recent years as they mean you can shoot long exposure images all day long. Furthermore the square filter system of this set-up enables you to stack filters - there are two available slots, so there is nothing stopping you from adding an ND grad (such as the supplied GND8 filter), a circular polariser or indeed stacking ND grads.
When it comes to ND grad filters, which are used for correctly exposing bright skies in landscapes, the type you use will depend on whether you have a cropped or full sensor camera. On a cropped sensor camera, a hard ND filter (like the one supplied with this kit) is a better choice than a soft one because the transition area of the filter will occupy a much larger portion of the frame than on a full frame sensor camera.
The filters are all coated with a special anti-reflective coating, which is important as you cannot mount a lens hood while this filter system is attached. I found the anti-glare capabilities to be excellent and once I'd imported the photographs into Lightroom I did not observe any problematic colour cast. White balance is easily corrected in post so this isn't a huge issue when shooting RAW anyway.
It's important to note that the K&F filters are made from highly polished optical glass manufactured in Japan, not the resin design, as used in some systems. In testing I found that this meant there were no issues with clarity or contrast and I was pleased with the neutral tones in the images I shot.
The only issue I have with the K&F system is that there is no way of locking off the filter holders rotation and so you have to be careful of misalignment on ND grads or circular polarisers, before taking the photo. However since you're highly unlikely to be using these filters hand-held, rather than on a tripod, it's certainly not a deal-breaker. Taking the filter holder on and off was extremely easy and can be accomplished one-handed if you hold the camera upright.