Facial twitch: I believe these twitches are similar to the twitches people get in their eyelids. Usually it goes away within 6 weeks or so. There are other causes such as caffeine, stress, alcohol, electrolyte imbalances and excessive fatigue. Feel better.
A shutter speed of 1/30 for example will let in twice as much light as a speed of 1/60 since it is two times slower. When you decrease the shutter speed by a factor of two you are increasing the amount of light by one stop. Remember that fractions get larger as the number on the bottom gets smaller.
The fastest shutter speed here is 2000th of a second, the slowest is 1 full second. The difference between each shutter speed is known as a stop, and either halves or doubles the amount of light allowed to reach the film. The B setting is used to keep the shutter open for a timed exposure of longer than 1 second.he light from the flash is emitted in a fraction of a second and the position of the subject at that moment will be isolated in the image. Don't use a fast shutter speed with flash. The recommended speed for most cameras is usually 60th of a second, or slower.