Photographers have used neutral density (ND) filters for eons to reduce the light reaching the capture medium (film or a digital image sensor) for a variety of reasons. Before the digital era, changing the type of film in your camera wasn’t very convenient or always possible, and mounting a trusty ND filter over your lens would let you shoot fast film (ISO 400 and above) on bright days by reducing its effective ISO. But even today, in the digital era, when you can change your ISO at the touch of a button, ND filters are still essential tools for exercising maximum creative control because, in many cases, they allow you to select the aperture and shutter speed you want regardless of the lighting conditions. 

To enhance that creative control and provide it in a more flexible and convenient form, Tiffen, the leading U.S. filter maker, developed an ingenious Variable ND filter with a continuously variable ring that lets you control the amount of light coming though the lens over a 7-stop range. It works by combining two polarizing filters, each optimized for precise color neutrality, in a single adjustable filter mount. By rotating the milled front ring on the filter with respect to a white index dot located on the fixed ring that screws into the lens, you can reduce the exposure from 2 stops (ND 0.6) to 8 stops (ND 2.4), or anything in between. There is a dotted scale in between the MIN (minimum ND) and MAX marks on the front ring for convenience in returning to a previous setting, but the scale is for reference only and not calibrated in ND values. Also note that while this filter uses the crossed polarization principle to achieve variable ND control, it is not a polarizing filter and will not work as such. It is, however beautifully made and finished, turns very smoothly and precisely, and is manufactured using Tiffen’s proprietary ColoCore technology that seals the actual filter material within the glass elements to ensure absolute uniformity in production.

One of the chief benefits of using the Tiffen Variable ND filter is in controlling depth of field. Here’s a good real-world example. We were recently shooting a portrait of a model on a bright sunny day with a 70-200mm f/2.8 telephoto zoom lens. We wanted to shoot wide open at f/2.8, to create a beautiful pictorial effect by blurring the natural background, and making our beautiful subject “pop.” However, even at our camera’s lowest ISO setting (ISO 100) and fastest shutter speed (1/8000 sec) the image would have been way overexposed if we shot at f/2.8, and we couldn’t achieve the visual effect we wanted at a smaller aperture such as f/4 or f/5.6. Variable ND filter to the rescue! We screwed a 77mm Tiffen Variable ND filter onto the lens, set the camera to aperture-priority (A) mode, set the lens aperture to f/2.8, and turned the front filter ring until the camera-selected shutter speed we wanted (1/4000 sec) was read out in the viewfinder, and took the shot. We also could have used S (shutter-priority) mode, selected the shutter speed we wanted first, and then rotated the front ring of the Variable ND until the aperture we wanted (f/2.8) was read out in the finder. Either way, the Variable ND provides an elegant solution to a sticky problem.

As you have probably figured out by now, another great use of the Tiffen Variable ND is for shooting at a slower shutter speed than you could otherwise set in order to blur motion in waterfalls, clouds, race cars, or any other fast-moving subject. Again, the problem is similar—even at the lens’s smallest aperture (f/22 or f/32) and the camera’s lowest ISO (typically ISO 100), you can't shoot at the slow shutter speed you want (say, 1/8 or 1/4 sec) without getting an overexposure in bright sunlight. Mount the Variable ND and it’s a breeze. I used aperture-priority mode to shoot my waterfall picture at a shutter speed of 1/8 sec by selecting A mode, setting the aperture at f/16 and dialing in the shutter speed I wanted by turning the front filter ring. It almost feels as though you’re adding another control to your camera. 

When it comes to actual imaging performance, the Tiffen Variable ND is outstanding in terms of image quality and color neutrality. In examining comparison pictures taken with and without the filter at high magnification, we could detect no discernible difference in overall sharpness, contrast, or detail rendition, nor did the filter seem to accentuate flare or ghosting. Any color discrepancy between pictures taken with and without the filter was barely noticeable—perhaps a hint of warming in some images we shot at or around the maximum opacity setting of ND 2.4 (8 stops under). Tiffen does recommends that you not go beyond the “MAX” mark on the front ring scale to avoid “an uneven exposure or color shift that appears as an ‘X bar’ on the image,” noting that this is more likely to occur when shooting at higher densities (ND values) on full-frame cameras or when using super wide angle lenses. We shot with it extensively on an APS-C-format Canon EOS 7D and never experienced this phenomenon, but in any case the cure is to adjust the focal-length setting of your zoom lens and rotate the filter ring until the color shift disappears. Tiffen also claims that the filter’s thin profile and wide outer ring helps to eliminate vignetting and based on our limited experience we agree. 

When we used the filter briefly on a 10-24mm Tamron ultra-wide zoom fitted to the Canon 7D we encountered no vignetting with that combo. However, it may occur with other lenses on other cameras and can be minimized by adjusting the focal length and/or filter position or recomposing the shot. Other hints and tips: Focus at the MIN density setting and then set the ND value you want, check your histogram to fine-tune the exposure, especially at high ND settings, take test shots based on manual exposure (M mode) readings, and when in doubt, bracket until you get the precise results you want. Our conclusion: The Tiffen Variable ND is a cool and useful accessory that belongs in every serious shooters gadget bag. It’s fun to use, and will last a lifetime if you keep it in its supplied protective case (which even has its own integral cleaning cloth), and treat it with reasonable care. Street price: Available in sizes 52-82mm at prices ranging from $109.95-$229.95.