Camera Speeds
The term speed is often used to refer to frames per second, or FPS. This concept is important to understand when speaking about undercranking, low fps, or overcranking, fast fps. The terms undercranking and overcranking originated from the days when a person literally had to crank the camera by hand, rather than by a powered motor. Undercranking will result in speeding up the action on the film when ran at normal speed, whereas overcranking will create the effect of slowing down the action on the film when ran at normal speed. Normal speed is 24 fps and that is the speed at which all modern day projectors run.
The following list of camera speed describes how a projector running at 24 fps will display the image, and also how each of the different camera speeds can be used.
Single Frame - used to show very slow action such as a flower blooming or bulding construction over a long period of time.
2-3 fps - Creates very fast, choppy motion. Can also be used for comical reasons.
4-7 fps - Still very fast motion, but a little less choppy than 2-3 fps.
8-16 fps - Images shot at this speed will start to appear as as though they are not sped up.
16-20 fps - Can be used to display a slight amount of speed in objects such as cars, planes, trains, etc. The average human eye will still be able to detect that image as being sped up at this fps.
20-24 fps - Probably will not be detected by the viewing audience as being sped up. Often used for action scenes such as fights.
24 fps - Normal projector speed. All action will appear normal and not sped up or slowed down. This speed is also used for synchronous sound recording.
24-30 fps - Action will be slightly slowed down at this speed.
30-48 fps - Used to slow down very fast action such as sports.
48-64 fps - Regular human actions such as walking will appear very slow. Also used in miniature sets to show mass in buildings.
64-96 fps - Used to slow down human and animal actions even more.
96-150 fps - Used for slow motion effects in film making. Also used to slow down quick action such as sports, for example to make a football action scene look like it is going in slow motion.
150+ fps - Used to film extremely quick actions such as explosions, and high-speed objects such as race cars and airplanes.
If you are tyring to find the right speed in order to slow down or speed up your image, it is best to try a couple of tests at different speeds and then monitor your results.
Other than speeding up or slowing down your image, some other possible reasons that you may change the camera speed would be to Change the exposure, increase or decrease the depth of field, or to shoot for video transfer.