Part II: Variable ND Filters

January 10, 2013 — Leave a comment

We just completed shooting a series of video tutorials that will be a kick-starter for the workshops we will be running on board the National Geographic Explorer during 2013. While shooting for broadcast clients, I generally shoot with a video cameras that are equipped with neutral density (ND) filters. These are internal to the camera and allow you to control a wide range of exposures that can handle from being in full sun to inside a darkened room.

We made a decision to shoot the tutorials with the cameras that will be featured prominently in the workshops, for me that is the Nikon D800. As we discussed in a previous post, the challenge is getting the correct exposure when you are restricted to 1/50sec shutter speed and a minimum sensitivity of 100 ISO, but still want to maintain that shallow depth of field that makes shooting with a large sensor camera so attractive. Without an ND, you are going to be over-exposed….

Of course the other advantage of using ND filters is taking longer exposures to allow moving elements in a picture to take on a soft moving effect. While taking a sunrise time-lapse sequence with the D800, this allowed me to use this effect sunrise across the ocean. Here is a frame from that scene.

We also discovered another quirk while shooting with the DSLR’s. The D800 allows you to make on the fly aperture changes while in video mode but my back-up camera, the Nikon D600, locks in the aperture once you start recording. If the lighting changes, you have to go out of live-view, re-adjust exposure and start again, not great when you are missing a shot. I was stunned to discover this choice made by the Nikon designers while we were out shooting and my immediate reaction was similar to many new users of this camera…. “what were they thinking when disabled this function!”. Then it suddenly dawned on me, this doesn’t matter as the variable ND saves the day for both helping with general exposure control on any camera, and in particular when faced with a dilemma like using the D600. You can simply dial in an exposure change by a twist of the filter.

I had been searching for the ideal filter as there are a wide variety of prices / quality combinations on the market. After reading reviews, I settled on the new Genustech Eclipse ND Fader. After testing the unit, we discovered it delivers good color reproduction, great optical quality and they produce the sharpest of pictures.

In the past I had made my own variable ND by stacking polarizers, it basically will do a similar job but the image sharpness was not as good, and perhaps more importantly, this answer did not give the low profile of the Genustech.  It works great on my Nikon 17-35mm lens without vignetting. Something my homemade ND failed to do.

Changing aperture during a shot while shooting video with a DSLR can present another challenge, even with a D800. Older style stills lenses that are fitted with click-stops at each prescribed aperture settings. Many newer lenses, don’t even have aperture rings as the adjustments are made through dials on the camera body. On professional video / film lenses there are no click stops and an ‘on the fly’ adjustment can be made smoothly to compensate for changing light levels.

For the professional film-maker or cinematographer, one great solution is to have your older stills lenses ‘declicked’ by companies like Duclos Lenses. But this means sending every lens to be adapted, plus any new ones that you purchase in the future. The cost is just not justified for many of us and guess what, the variable ND comes to the rescue once again! No preset clicks, just a smooth adjustment that will decrease your light levels by 2 to 8 stops.

Variable ND opened up

Variable ND closed down

So despite the fact that I mentioned this in a previous post, I will say it again, the variable ND is a must have item in your camera bag and would recommend the new Genustech Eclipse ND Fader!

PS (From my frugal Scottish ancestors) Buy the filter that covers your largest diameter lens, as well as some step up rings so that the same filter will fit smaller lenses in your kit.

Photo credit: Barbara Krauss

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