This Tiffen Variable ND filter is one of the most commonly used ND filters for mirrorless hybrid and DSLR shooters.
Neutral-density filtration. Why would we want to discuss something as boring as ND filters? Simple, because the times, they are a changin’ and along with them, how we think about ND filters is also changing. Depending on which type of camera you predominantly shoot with, your view about neutral-density filters may be different. If you shoot with a mid-level camera, something like a Blackmagic Ursa Mini Pro G2, Canon C200 or a Panasonic EVA 1, neutral-density filtration is built into your camera in the form of a filter wheel.
The equation is really pretty simple, we use ND filters to reduce the amount of light reaching the sensor, allowing us to operate our video and digital cinema cameras at a more typical shutter speed, often at 180 degrees. If you set your camera to record in 24p (really 23,976) fps, following the 180-degree shutter rule results in a 1/48th of a second shutter, right? You can extrapolate that rule to apply to any other frame rate that you shoot, the 180-degree rule of doubling the frame rate with the shutter speed will give you a shutter angle or speed that’s complementary to creating the typical look of shooting a film camera.
Shutter Speeds/Angles and Exposure
Of course, rules are made to be broken and I often do. It can be fun to under crank a camera’s frame rate (wow, under crank, words that harken all of the way back to the silent film era’s hand-cranked cameras) and let the shutter stay open for longer, resulting in a smeary, blurry look that’s perfect for a drug or alcohol-induced haze on a character’s POV shot. Of course, conversely, you can decrease the shutter’s exposure by speeding it up, giving you that surreal “Saving Private Ryan” beach jittery look that has its own surreal visual signature.
Typically, though, we mostly try to stick to the 180-degree rule for most shots for most projects, unless something “different” or “edgy” is called for in the script or concept. If you have a background in photography, you know that the relatively slow shutter speeds we use compared to the shutter speeds that still photographers use results in a LOT more light coming into our sensor. If we’re attempting to keep the shutter speed on our camera in the 180-degree neighborhood, that means we only have two other ways to reduce exposure, reducing the lens aperture or reducing the camera’s ISO or gain (sometimes also ASA for film stock if you’re still shooting film).
The other way to reduce the amount of light hitting our sensor or film stock is via ND filters. Neutral density only exists to reduce the light hitting the imager, hopefully without coloring or otherwise adversely affecting the image, hence the “neutral” in the name.
Neutral Density For The Low-End And High-End Camera
If you shoot with a removable lens mirrorless/DSLR camera or high-end digital cinema camera like a RED or Arri Alexa, none of these cameras offer internal ND. You have to buy external ND filters and somehow affix them to the lens, either a circular ND filter that’s fastened to the lens front via threads or with a matte box that you use to insert rectangular glass filters into slots in the matte box. There are a few specialty lenses where the front element of the lens protrudes too far out to physically mount a filter in front of the lens. Some lenses of this type have a small slot at the rear of the lens where the diameter of the lens barrel is smaller so that a small ND or another type of filter can be inserted into the lens barrel, providing the same light-reducing effect as the larger filter at the front of the lens.
What An ND Filter Does And How It’s Implemented
If you think about it, ND systems are one of the more primitive systems on a modern digital cinema camera. It’s either an external piece of darkened glass that’s affixed to the front or rear of the lens or it’s a wheel of small ND glass filters in a wheel inside the camera that rotates, typically on a turret, to place the selected ND strength in front of the sensor. Both systems are primitive compared to the rest of the electronics in the camera, which are some of the most sophisticated electronic systems outside of military hardware and aviation. Why is it 2020 and barely any companies have moved from either of these mechanical paradigms used for reducing the light that reaches a sensor?
Enter Z CAM Electronic ND Filter
You may or may not be familiar with the Z CAM lineup of digital cinema cameras. Z Cam is a Chinese company that has only been on the scene for a relatively short time, yet their popularity has grown quickly as their camera systems offer professional cinema camera features at a small fraction of the cost of a traditional cinema camera from Canon, Sony or Panasonic. Z CAM offers several camera models with Micro four-thirds, S35 and Full Frame sensors and they just introduced an optional accessory for their cameras called the Z CAM E-ND Filter.
I believe this new electronic filter is very innovative and offers an ND range of 1.7 to 6.7 stops of ND filtration in 1/3 stop increments. The advantage of electronic ND is that it has much more precise control over its ND strength over traditional Internal NDs that typically are set up only in 2-stop ND increments. The E ND sells for $399 and is easily integrated into the Z CAM lens mount with just two screws. The electronic ND filter will be implemented in all of the Z CAM E2 flagship models—E2, S6, F6 and F8—with EF-mount or PL-mount. What I find innovative about this ND system is that it’s electronic, so the ND ramping in 1/3-stop increments is smooth and seamless, easily controlled in the Z CAM menu. The addition of this accessory into Z CAM lineup immediately elevates their image and feature set, strengthening the case for considering a Z CAM instead of their competition.
The Sony Electronic Variable ND System
Sony has implemented an internal electronic variable ND system on three cameras to date, the PXW FS5/MKII, PXW FS7 MKII, PXW Z190/Z280 and the PXW FX9. Unlike the mechanical filter wheels that its competitors use and even Sony uses on its top-of-the-line Venice camera, these models utilize an infinitely variable electronic ND that can easily be adjusted via an access wheel at the front of the camera.
The Variable ND can also be set to auto ND to track a particular exposure value, allowing the user to set ISO, aperture and shutter speed and keep them constant with the camera ramping the ND filter to track a particular exposure through radical lighting changes. It allows for internal recording for time-lapse, allowing the camera to seamlessly change ND values as exposure changes for night to day and day to night shots, etc. I had a chance to utilize the electronic variable ND on the FX9 as I recently used it for several shoots and I walked away impressed at the versatility and ease of use with the system. It was painful to go back to my traditional camera with its internal fixed 2-stop ND filter wheel afterward.
Where From Here?
I think that much like autofocus technology that just a few short years ago was unthinkable to implement on a professional camera, Electronic Variable ND is the future for all cameras. When competitors to Z CAM and Sony see what sort of buyer feedback the companies receive about features like Electronic Variable ND, they’ll begin to see that having it on a camera is a competitive advantage.
This should lead them to implement their own versions on their own camera lines, and the end benefit for all of us is that these kinds of features get out of the way of creativity and automate functions that we once had to concentrate on ourselves. Once you have used this technology, you begin to not notice exactly how many stops of ND you have dialed in; you just check using your exposure measurement tools (waveform monitor for me!) and dial it in until it achieves perfect exposure. These features give you more control, in the end, control over your exposure value, shutter speed, ISO and aperture. It’s a fourth variable to adjust exposure, which is, in itself, a radical idea.