Tip of The Week: Using ND filters for videoTips
Every Thursday, we post a photography-related tip on our blog. These tips are typically inspired by questions we get from our customers. Sometimes we might feature a technique tip, and sometimes a gear recommendation. If there’s something specific you’d like to see in this section, let us know. Email us at [email protected]
This week’s tip is directed at those of you using HDDSLRs to shoot video. As many of you know, cameras like the Canon 5D Mark II and the Nikon D7000 can shoot up to 1080p video at 30 (or the more ‘cinematic’ 24) frames per second. With the introduction of these cameras into the video world, a number of photographers are starting to expand beyond stills, which means they have a whole new set of factors to consider.
One thing that confuses a lot of photographers is that in the video world, shutter speed is no longer something you can use to control your exposure – at least, not without additional consequences. When shooting video, your shutter speed needs to be fixed at either 1/50th of a second (if you’re shooting video at 24fps) or 1/60th of a second (if you’re shooting at 30fps). The reason behind this goes back to the old film days and the way the 180-degree rotating shutter worked on old film cameras. Tyler Ginter has an excellent post detailing how this works on his blog, if you’re interested.
Bottom-line: you have to shoot at a fixed shutter speed, which means you have to control exposure through the use of your aperture and ISO settings. For lower-light situations, this is ideal; you can shoot with your shutter wide-open and keep jacking your ISO up to get the exposure you want, since the low-light performance of bodies like the Canon 1D Mark IV are quite amazing.
But when it comes down to a question of too much light (say, at high noon, for example), videographers often have a problem. You can shut down your aperture, of course, and pull your ISO down to 100 (or even 50), but at some point, you hit a wall and can’t go any lower on ISO or smaller on your aperture. Also, sometimes you don’t want that small aperture and its deep depth of field. Sometimes you want a really shallow depth of field at high noon.
That’s where the most important filter used by filmmakers comes in: the Neutral Density filter.
An ND filter cuts the amount of light coming into your camera, allowing you to shoot at the aperture you want. ND filters are measured by the amount of light they cut out and that measurement is measured in f-stops. So, a 1-stop ND filter would allow you to get a proper exposure at f/2.8 instead of f/4, or f/5.6 instead of f/8. 2-stop ND filters would let you go from f/5.6 to f/2.8, and so forth.
ND filters come in various degrees of opaqueness. BorrowLenses rents a number of them, mostly in the popular 77mm size. They are available in 1, 2 and 3-stop versions, as well as a variable model that allows you to go from 1 to 8 stops by rotating the filter.
The video below shows the effect of a Variable Neutral Density filter on exposure. Watch as we go from an overblown shot at f/2.8 to a perfectly exposed shot without changing camera settings, just by rotating the front part of the Variable ND filter to cut the light down.
Of course, ND filters have other uses too. Landscape photographers use them to get flowing water to show up as silky sheets, rather than freezing the water in mid-motion. Portrait photographers shooting into the sun can also use them with a combination of flash to match ambient light with their subjects. But for video photographers, the ND filter is the first filter they add to their arsenal.
Try this: Stick a neutral density filter on your lens and try and shoot a quick video at the widest aperture setting you can while staying at 1/50th of a second at ISO100. Now take the filter off and see if you can repeat the process (hint: you won’t be able to, not without completely overexposing your video). That will give you a good idea of this concept in practice.
One caveat with using Variable ND filters is that sometimes, they can either leave a color cast on your video, or they can reduce the sharpness of your lens. Since Variable ND filters have two pieces of glass instead of just one, that’s two additional pieces of glass in front of your lens. Using single-setting ND filters usually takes care of this issue.
That’s it for this week’s tip! If you have any questions or comments, please email them to [email protected]