Shutter Speed vs Frame Rate
A common cause of confusion in video cameras is shutter speed vs frame rate (frames per second, or fps). These are not the same thing and are basically unrelated.
- Frame rate = How many individual frames are created each second.
- Shutter speed = How long each individual frame is exposed for.
Most cameras have a single set frame rate which depends on the TV standard of the country they are manufactured for. PAL cameras use 25 fps, NTSC cameras use 30 (29.97) fps. Some cameras can swap between frame rates, some cameras are geared towards theatrical frame rates (e.g. 24 or 48 fps), and some specialist cameras can have a very high frame rate (e.g. super-slow-mo cameras operate at 75 or more fps). In most cases though, your camera will have a single set frame rate that you never have to worry about.
Shutter speed can be adjusted on any good camera equiped with manual controls. Although the default setting is fine for most situations, it's nice to have the option to change it.
The image below represents one second of video consisting of 25 frames. Each frame is represented by a vertical black line. This video is 25 fps—25 frames for each second of video. If the video was 30 fps there would be 30 black lines slightly closer to each other.
The blue bars represent shutter speed (the time that the shutter is open). There are three different shutter speeds shown.
- At a setting of 1/25, the shutter is "open" for 1/25th of a second. This is the same as the frame rate so the shutter is open for the entire duration of each frame.
- At 1/50, the shutter is open for 1/50th of a second which is half the duration of each frame.
- At 1/100, the shutter is open for 1/100th of a second which is quarter the duration of each frame.
Think of the "missing time" as a gap between when the shutter closes and when the next frame begins.
As you can see, the shutter speed can be varied without affecting the frame rate. If the shutter is open for a shorter time, it's closed for a correspondingly longer time. The total always equals the frame duration.
Longer Shutter Speeds
You may wonder about shutter settings that are longer than the frame rate. This is possible and is used either for effect or to compensate for very low light. In this case multiple frames are effectively merged together to accommodate the longer shutter speed.