Cinematographers are generally interested in making their films appear in real time, as a way to emulate reality, but occasionally for storytelling purposes it makes sense to slow time down or speed it up in a scene. Adjusting your frame rate or frames per second (fps) is the easiest way to control how a character’s motion is captured for the screen.
This piece and the video at the bottom of this post from In Depth Cine, explain the basics of frame rates in filmmaking such as, for example, the difference between 8fps and 120fps.
What Are Frame Rates?
The images that make up a film are essentially just a bunch of individual still frames that when played back appear to be moving. Back in the day, frames were captured on rolls of film. These days when people talk about frame rate they are typically referring to how many frames per second a camera can capture, but this is only half of how frame rate works.
Motion can be manipulated in two ways: the capture frame rate (which is adjusted in camera) and the playback frame rate, which determines which speed the captured frames are played back. Adjusting these two things gives you a chance to adjust footage to appear in normal motion, slow motion, and fast motion.
If a clip is shot at 24fps and played back at 24fps it will appear normal to the human eye. If a clip is shot at 48fps and played back at 24fps, it will be played twice as slow as normal. If the camera is capturing the clip at 12fps and has a 24fps playback rate it will be moving in double time. Most cinematographers choose to adjust their capture frame rate on the camera to elongate or speed up time.
Common Base Frame Rates
The majority of film projects use a base frame rate of either 24p, which is based on the standard film exposure rate of 24 frames per second, or 23.976p, which is based on NTSC format televisions. 25p is the frame rate that is typically used for PAL format televisions. A higher base frame rate will eliminate motion blur and give you images that are crisper during playback. The Hobbit, for example, was shot and displayed at 48 fps.
Popular capture frame rates for two times slow motion footage include 48fps or 50fps, while 33fps will give a more subtle slowed down effect. Frames rates like 100fps or 120fps will give you extremely slow motion footage where time will feel like it is standing still.
Changing frame rates while shooting gives you flexibility to use techniques like step printing, which uses a very low frame rate and instead of printing each frame one time, each frame is printed three times. This technique is a great way for communicating the chaos and anxiety of an action scene with lots of movement.
Slow motion footage is another way that filmmakers often add drama to their action films. To accomplish this, filmmakers are usually shooting anywhere between 100fps all the way up to 360fps. The slowed down speed adds a level of intensity and focus to scenes that are happening quickly.
A fast motion shot, on the other hand, can be used to isolate individual characters and force viewers to focus in on them. One creative way to do this is to shoot at a low frame rate, play back at a higher frame rate, and have your main characters stand still or move incredibly slow while you are rolling. This can give the illusion that everything around them is moving swiftly around them while they appear stuck in time.
Learn more in the excellent video below from In Depth Cine.