Introduction
If you’ve shot cinema, or even enthusiast level video, you know the importance shutter speed has on the visual charm of your films.
In photography, shutter speed can often be an afterthought unless aspiring to freeze fast motion, induce blur, or produce long exposures for visual effect. Outside of those use cases, often a photographer’s direction is just to keep it within a specific safe range.
Cinema, however, is different. Ever noticed how when you started out in video, or purchased your first GoPro, how awfully ‘digital’ the image looked? People jump straight to learning log colour grading, or adding crop marks to try and pro up the image, but in almost all cases, this digital look is due to shutter speed.
Shutter angle in film
When shooting video, shutter speed is rarely referenced, and instead we look for the shutter angle, aspiring to get it as close to 180 degrees as possible. You see, shutter speed is an absolute term, defining the duration in which the shutter curtain remains open (or partially open) for, whereas shutter angle is a relative term that corresponds to the actual frame rate of the film, and is usually double.
For example, for a film shot at 24fps, to maintain a 180 degree shutter, you would need to shoot at 48fps to achieve this. There’s a multitude of reasons for shooting with a 180 shutter, but the primary purpose is to obtain the smooth & cinematic motion blur synonymous with Hollywood and indie cinema. This property is one of the major contributors that will make your films look like they were shot and produced professionally.
The two examples below show two clips with identical framerate shot at two different shutter angles that visually represents the effect this has on motion.
Why neutral density filters?
Exposure has three primary elements referred to as the exposure triangle. ISO, aperture, and shutter. With variations in ISO affecting dynamic range and visual noise, and aperture controlling visual depth of field, in photography you’d usually adjust your shutter speed to compensate for fluctuations in exposure. But as stated above, shutter speed is now a major component of the ‘look’ we’re going for. We can vary our ISO and aperture to combat minor changes in scene brightness, but often these are selected out of necessity or required aesthetic.
Naturally, there’s room for a fourth component in the exposure triangle, and that is neutral density filters. Think of them as sunglasses for your camera, that can control how much light makes it to your sensor, so you can focus on how you want your shots to look rather than compromising aesthetic for exposure.
K&F Concept ND2-ND400 Neutral Density Filter
For a couple of weeks I’ve been using K&F’s Nano Series Variable ND, providing up to 9 stops of light reduction, and advertising slim frame, multilayer coating, scratch resistance and no x-pattern, a common problem with variable ND’s due to their dual polarising construction.
Prior to being introduced to the K&F model, on my Blackmagic Pocket Cinema Camera 4K I was using the 82mm Zomie Vari-ND, which left a lot to be desired and a skeptical view on Vari-NDs when compared to the reliability of the square and rectangular filters placed inside matte boxes. The K&F model has very clearly undergone elaborate R&D, as a lot of the shortcomings found on the Zomie and other entry level ND’s are mostly absent in this model.
Side profile of the K&F Vari-ND, showing the raised orange putter for simple operation.
The green reflection of the filter’s nano-coating, preventing internal reflections.
The design
Immediately after taking the filter out of the box, the construction quality was instantly apparent. The chassis is made from high quality metal, with the variable ring having a user-removable orange putter to assist with precise control, whilst also providing an extra measure to prevent fingerprints from accidental contact on the glass which is a huge plus.
Frame & vignetting
The filter frame, although still thing, is not as slimline as other filters on the market which originally had me concerned for vignetting, however the filter’s outer diameter is substantially larger than comparable filters with the same nominal diameter, which completely removes the frame from the lenses field of view, even when shooting at the widest setting of 24mm. This is a great design that I wish more manufacturers pursued, and gives you the confidence to be able to shoot at any focal length throughout the range of your lens.
Nano coating & flare
What really stands out is the nano-coating used on the glass to prevent internal reflections and glare. One of the major downsides of using a Vari-ND is their impracticality to run inside a mattebox, as being able to adjust the density on the fly can be fiddly in the cramped space of the hood. No matte box means no protection against incidental light striking the lens, and can quite often wash out or ruin your shot as you deal with light leak and flare circles. Since acquisition of the Blackmagic camera, I’ve had to actively avoid shooting into bright light sources like the sun, as the blooming from my previous filters would be unusable, creating a very poor quality image. Not too dissimilar to what you’d get out of an iPhone.
In our recent episode of Plant People linked below, a large portion of scenes were shot in the direction of the sun, with a lot of light striking the surface itself. I found under nearly all conditions that the filter performed flawlessly, controlling bloom and flare patterns almost as good as the naked L series 24-105mm f/4L IS lens itself. This was a very welcome discovery, and something all filmmakers will require.
Packaging
Like most of the new content from K&F, the filter comes in a nice hard cardboard magnetic box which has a satisfying snap as you open and close the latch. Boxes are often tossed aside and thrown to the trash, but I’ve found myself holding on to the K&F variants for long term storage on camera shelves. The pouch provided to store the filter in is a nice touch, but as mentioned in previous reviews, feels slightly lower quality being made of faux PU leather. The quality however is still fine for its purpose, and is more than enough to keep your filter safe, even if thrown precariously into a bag and forgotten about. They’re a nice throw in.
Light reduction
In use, the filter itself did exactly what it was advertised. It provided the full range of light reduction written on the box, however the “No x-pattern” claim was optimistic as predicted. Given this is a dual polarising filter as mentioned above, this isn’t surprising, nor disappointing. Especially as there’s roughly 7 stops of usable reduction before any shot destroying X bands enter your image. By this point, it’s safe to jump to the next of the dual ISOs found in the BMPCC4K making this a complete non-issue.
ND2, the lightest setting whilst reflecting direct daylight.
ND400 notice the nano coating reflecting the incoming light.
ND2 with no ambient light reflections. Notice no colour cast from nano coating.
ND400 blocking almost all transmissible light. Perfect for high base ISO cameras.
In camera is where this all really matters. Where there’s foreign glass in front of you lens in the place of a filter, there’s a risk of colour cast. This risk increases exponentially the darker the filter gets, as more light can be rejected at uneven magnitudes across the various wavelengths. So far, 2 weeks into using this filter I have found the colour contamination is almost non-existent, and is very consistent throughout the range. Overall there’s a VERY slight shift toward green, but correctable by 2-3 points of tint in the on-camera white balance setting. A slight tint shift is uniform across all filters I’ve used, some worse than others, and I’d say the K&F is operating on the barely noticeable end of the spectrum.
Unfiltered lens exposure and colour. Captured from Atomos Ninja V monitor.
With K&F ND filter mounted and set to approximate 4 stop reduction.
Usually when using an ND filter, i’m between the range of 2-5 stop reduction. The above shots off the Atomos Ninja V monitor show the indistinguishable colour shift from the filter, as well as the effectiveness of uniform light reduction across the scene.
Conclusion
Neutral density filters are a must have tool in any filmmakers kit, and a Vari-ND is one of those products you’ll wish you had if you don’t, and be grateful for every time you use it if you do. Their versatility, compact size, and overall aesthetic bring professional level video to something even as rudimentary as a budget DSLR or Mirrorless camera. K&Fs execution of their Vari-ND is one of the best on the market for the price, and has the image quality and features of their much more expensive competitors.
For the money, you can’t go wrong, and at this stage I’d even struggle recommending a better option, even with an unlimited budget. Check them out at the link below and be sure to select the filter thread that suits your largest lens, as it’s easy to step down a size with adapter rings, but impossible to go up.
Be sure to watch the latest episode of Plant People, embedded below to see the how these filters perform in indie cinema.