What is motion blur?

A video camera doesn't capture an instant: each frame is exposed for as long as the shutter stays open. Anything that moves during that time is recorded as a streak, which is motion blur. The shutter speed, or shutter angle on cinema cameras, sets how long each frame is exposed, and with it how smooth or choppy movement looks on playback. The classic 180° rule sets the shutter to half the frame interval, for example 1/48 s or 1/50 s at 24 fps, which gives the motion blur viewers know from cinema.

Tool description

This tool works out the motion blur you get from a frame rate and shutter, and shows it in an animated preview. Enter the shutter as a speed, as on photo and mirrorless cameras, or as an angle, as on cinema cameras, and get the other value, the exposure time, and the 180° rule shutter for your frame rate.

Features

  • Takes the shutter as a speed or an angle and converts it to the other at any frame rate
  • Plays a preview of a moving subject at your frame rate and shutter, blurred the way the camera records it
  • Describes the look, from choppy to smeared
  • Gives the exposure time and the 180° rule shutter for your frame rate
  • Runs in your browser

How it works

The exposure time is 1 / shutter speed, or shutter angle / 360 / frame rate. The shutter angle is the share of each frame's movement that gets blurred: at 180° a moving subject's streak covers half the distance it travels between frames, and at 360° the streaks join up. The look is natural within ⅓ stop of 180° (about 143° to 227°), crisp down to 90°, choppy below that, and smeared above. The preview moves a subject across the frame in one second, steps it forward one frame at a time, and blurs each frame over the exposure time.

Tips

  • Most cameras can't set 1/48 s, so use 1/50 s at 24 fps. The difference is too small to see.
  • For slow motion, use the 180° rule at the recording frame rate, such as 1/250 s for 120 fps.
  • In bright light, use an ND filter to keep the shutter near 180° instead of switching to a fast shutter.
  • If you want to pull sharp stills from the video, use a fast shutter and accept choppier motion.
  • Under mains-powered lights, pick an exposure that spans whole flicker cycles to avoid banding: 1/50 or 1/100 s where the grid is 50 Hz, 1/60 or 1/120 s where it is 60 Hz.