Remember this simple formula and set the correct shutter speed every time you’re recording:
SHUTTER SPEED = FRAMES PER SECOND (FPS) x 2
For example, if filming at 23.976 FPS, multiply 23.976 x 2 = 47.952, so your proper shutter speed should be 1/48 sec. If your camera doesn’t have that exact shutter speed stop, round it up to the closest available, which is 1/50 sec. This will give your footage a natural motion blur.
You might have had certain clips or sometimes entire series declined by the editors saying that "the motion is off," or you’ve used an incorrect shutter speed. What does this mean? Visually, this means that the motion blur looks unnatural.
We can thank Hollywood for "training" us to perceive motion in a certain way when we view moving images. What we perceive to be “natural” is a rate of 23.976 frames per second (commonly rounded up and referred to as 24 FPS). This is the frame rate traditionally used in film, video and television that we call "cinematic."
Incorrect shutter speed will result in unnatural motion blur, which can be jarring for fast shutter speed settings or may have a “smeared” or “trailed” blur if using a slower one.
On BlackMagic Cinema Cameras (4K and 6K) or more high-end cameras, you can also set the shutter speed using shutter angle degrees as you might be used to in photography. Without going into too much detail, the shutter angle is a carryover from how traditional film cameras adjusted their mechanical shutter angle opening according to the frame rate.
A shutter angle of 180 degrees is equivalent to the 1/48 shutter speed when filming in 23.976 FPS. The 180-degree angle shutter will have an equal amount of time open, exposing the sensor (or film frame) as it is closed. It’s a half/half ratio.
On BlackMagic Cinema cameras setting and leaving the shutter angle at 180 degrees will keep a consistent motion blur regardless of the frame rate.
The formula will help us find the correct shutter speed when we want to record slow-motion movement.
If you are recording at 120 FPS, follow this formula:
120 FPS x 2 = 240 or 1/240th
So set your shutter speed at 1/240th of a second or round up to 1/250.
Increasing the shutter speed when filming at high frame rates will lower the exposure, so make sure to record only if you have enough light to expose your image properly.
Filming in Broad Daylight
Filming normal movement at 23.976 FPS, using a 1/50th sec shutter speed in broad daylight will overexpose your image. To fix this, you can:
- Stop down the aperture or the ISO, or
- Use a good quality ND filter to cut down the amount of light hitting the sensor. Using higher f-stop ND filters on certain high-end cameras like the Ursa Mini 4.6k, Alexa Classic, and some older Red cameras, will cause some infrared (IR) issues, shifting shadows with a magenta tint and altering the green hues. In that case, using a good quality IR cut filter in conjunction with the ND filter should take care of the issue.
We hope this will help you understand how to set the proper shutter speed depending on the frame rate you’re filming at and record some insanely good footage!