One of the tricks you can pull off with a decent mirrorless or DSLR camera and a tripod is a long exposure shot. What we mean by that is anything longer than you could practically shoot hand-held – so all the way from 1/3rd of a second up to minutes and beyond. Being able to dial in your exposure time is often accomplished using a combination of ISO and aperture, the lower the ISO and smaller the aperture, the longer the exposure will have to be. However it’s not always desirable to rely on the aperture/ISO balancing act to fine-tune your exposure time and it’s for this reason that photographers use ND filters.
Having a decent ND filter or two in your bag is pretty much essential if you’re a landscape photographer, because they enable you to control exposure time without having to compromise your aperture or ISO settings. Traditionally those ND filters come in individual strengths and sold according to the number of stops of light that they block. That’s fine, but light is constantly changing and you often find yourself switching ND filters in and out as the amount of natural light in the scene changes. All of which makes a variable ND filter, in which you can dial in the number of stops you require, a great idea.
Mastering the Light
The K&F ND2-ND400 is a 9-stop variable ND filter. This means you can dial-in any ND ‘strength’ between ND2 (1-stop) and ND400 (9-stops). This variable design is accomplished by using two pieces of polarised glass sitting on top of each other. As you rotate the front piece of polarised glass the image becomes darker and darker until you reach the maximum number of stops for that filter.
Let’s say you’re shooting an image at f/8 that the camera has metered for one second with no ND filters on the lens. If you dial in the variable ND filter to its base ND2 the camera will now meter for four seconds, stretching out your exposure time without having to change ISO or aperture. If your naturally metered one second exposure is dialled in for ND400, the camera would meter for about eight minutes. Therefore with a variable ND like this one on your lens you have a huge amount of flexibility in getting the light hitting the sensor at exactly the levels you want.
I’ve had a couple of variable NDs over the year and I have to say that the K&F ND2-ND400 is the nicest I’ve used. The adjustment buckle is curved to fit the finger making it much easier to dial in the right ND number by rotating the filter in the same way that you would a circular polariser. It’s also much slimmer than my old ND filters which means that even with my super-wide 10-24mm wide open, there’s no vignetting from the edges of the filter.
When I tested it I didn’t observe any colour cast from the filter and its Japanese-manufactured glass. I also great appreciate the scratch-resistant design because my filters always seem to suffer from scratches and dings from being taken on and off and thrown around in the camera bag. If you’re a bit clumsy like me then you’ll also appreciate the Nano coating which is resistant to finger-prints. The only drawback to these filters (and it’s true of all variable NDs) is that if turn the dial past the marked end-point at ND400 the polarised glass will go out of alignment and you’ll see heavy vignetting on either side of the frame. It doesn’t hurt the filter in any way – in fact you can rotate it a full 360º if the mood takes you – but you just need to be aware of it when you’re dialling in the number of stops.
If you’ve been frustrated by ND filters in the past and don’t enjoy all the faffing around that comes with switching out the glass then a variable ND like this is the way to go. These K&F filters are reasonably priced and suffer from none of the drawbacks (such as a noticeable colour cast) of other entry-level filters. The K&F ND2-ND400 takes up virtually no room in the camera bag, can be purchased for lens threads between 62mm and 82mm and comes with a great little leather case to protect it when it’s not in use.