When you get to the point in your skills where you’re about to switch from shooting video on your smartphone to a DSLR or mirrorless camera, it’s time to learn about the exposure triangle. It’s a concept as old as photography itself. It consists of balancing aperture, ISO and shutter speed in order to expose an image. However, when it comes to video, almost every tutorial, including ours (see below), gets it wrong. That’s because, for video, shutter speed is usually something you set once and don’t change. That leaves video shooters using a DSLR or mirrorless camera with only two adjustments to make to exposure.
We didn’t always have this problem. In the old days, before video cameras and still photo cameras were the same devices, professional and prosumer cameras gave video shooters three tools to adjust exposure: iris (a.k.a. aperture), gain (a.k.a. ISO) and neutral density (ND) filters. Sure, you could adjust the shutter speed, but shutter control was usually not easily accessible.
Motion picture film cameras were similar. Generally, you’d load the camera with film at the ISO sensitivity you needed, set the aperture then applied ND until exposure was correct. The shutter was a spinning disk with an opening cut out. You could adjust the shutter by removing the lens and using a special tool, but most of the time, the shutter was set to 180 degrees, or double the frame rate.
Today professional videographers and filmmakers at all levels are commonly shooting with DSLR and mirrorless cameras, which don’t come with ND filters.
Most professional digital filmmakers know to keep the shutter speed at double the frame rate, or at the very least a consistent speed across several shots. That’s because an edited video that has different shutter speeds throughout is jarring to viewers.
Once you know to set your shutter speed and leave it alone, exposing video becomes difficult without an ND filter. This is especially true during shoots with high-intensity light — i.e., outdoors during the day. ISO only goes so low and giving up the option to shoot with shallow depth of field sucks.
Our advice is for shooters to purchase a variable ND filter. Doing so gives you the complete exposure triangle for video: aperture, ISO and ND.