Using Neutral Density Filters for DSLR Video Production
During our adventure into shooting video with a DSLR such as the Canon EOS 7D one of the recent things we looked at was that you should maintain a shutter speed of twice the frame rate to achieve the best visual results. The challenge is that are working with relatively long shutter speeds of 1/50th or 1/60th of a second which in bright sunlight may be difficult from getting overexposed even with a small aperture and low ISO setting. If we are still too bright the best way to get down into the working range that we want is to use a neutral density filter.
Practical Uses of ND Filters
Some photographers, especially nature and landscape photographers have long been familiar with neutral density filters most notably for allowing you to shoot a scene with a longer shutter speed for scenes such as waterfalls to get that silky effect to the water.
If we go back to the basics and look at the Sunny 16 Rule, this tells us that is bright sunlight at ISO 100 and 1/100th shutter speed, we will need to be at f/16. If we adjust our shutter to our video setting of 1/50th, then we need to be shooting at f/22 for a proper exposure. While this may work in some situations, if you want any creative control over your aperture settings, you will need to cut down the lighting entering the camera, again this is a great use of ND filters. Instead of using a faster shutter, we can simply use darker ND filters to cut down the light to where we want it.
Choosing an ND Filter
Most neutral density filters are fixed at a particular setting and generally come in settings from 1/4 stop all the way to 10 stops. Buying a small selection of ND filters is certainly one option, although a much more versatile option would be a variable ND filter that lets you adjust the density across a wide range.
The Variable ND Filters from FADER are an excellent example of this type of functionality. With the FADER Filters you have a range of 2-8 stops which, if we go back to our Sunny 16 Rule, only needs four stops to allow us to shoot at f/2.8. This allows us a broad range of creative control with your aperture.
At a bit over $300, these filters don’t come cheap so if you are on a budget you might want to get a couple of less expensive ones to start off with.
Using an ND Filter
There is nothing special or magic about using an ND filter, once it is on your lens it’s just as if someone dimmed the lights and you continue to set your exposure using aperture and ISO adjustments (remember, not shutter speed because we are locking that down to 1/50th second).
The following video demonstrates this concept by shooting the same scene and adjusting the FADER filter to make the scene darker while opening the aperture to compensate.
I hope you are enjoying these articles on getting started with DSLR video. Even though shooting video with a camcorder or other dedicated video camera is so easy that even a kid can do it, shooting video with a DSLR is actually quite complicated and requires a very different skill set than shooting still and often requires specialized gear to get top-notch results. If you are doing any video work, please post in the comments and let everyone know what you are doing.