# focal length vs shutter speed vs fps [duplicate]

I'm confused about the relationship between focal length and shutter speed, and the relationship between shutter speed and FPS. Can somebody explain in more detail here? What I read is that `shutter speed=1/(2*fps)` at least, while `shutter speed=1/focal length`.

Edited If i have an ip camera of 640x480(sensor width =3.6mm), focal length from 5 to 50mm, need to record 30fps, what is the best shutter speed to be use?assuming that the object distance to camera is 60ft.

• Are you doing stop motion, or video? Mar 14 '13 at 13:57
• I need to record a video with moving object. the object must not be blurred by motion blur.
– user17752
Mar 14 '13 at 14:20

The quantity that most commonly relates the two is camera shake. It is often advised that to avoid camera shake the shutter speed must be `1/focal-length`. This is presumably where you've gotten this equivalence from. The rule is a guideline only and depends on your technique and degree of enlargement in the final image. A better guideline is `shutter-speed = 3/focal-length`
FPS, or frames per second is the number of images per second recorded by your camera. It is related to shutter speed in that `shutter-speed + latency < 1/FPS`. If each frame takes more than a 60th of a second to expose, then you are not going to be able to cram more than 60 exposures in a second! There is a nonzero amount of time required to recock the shutter mechanism (if necessary) and readout and store the image, which is the latency. In stills cameras not designed for continuous readout the latency can increase as buffers become full, causing the maximum obtainable FPS to drop.
The formula `shutter speed = 1/(2*FPS)` relates to a shutter angle of 180 degrees, which is a concept from film cine cameras whereby the film can only be exposed for a maximum of half the intra-frame time, because of the rotating shutter. This rule is still obeyed by digital filmmakers to ensure "cinema like" motion to the image, compared to if `shutter speed = 1/FPS` which gives more fluid "TV like" motion.