Most modern (SLR) cameras use focal plane shutters, which have gone through quite a bit of evolution over the years, trying to get over mechanical limitations -- there's only so quickly that you can accelerate/decellerate physical matter in a confined space in a short amount of time. The modern focal plane shutter works by having two shutter curtains, one moving slightly ahead of the other. As with interlaced video this can lead to some artifacts when things change during the frame. Including interesting looking helicopter blades. (Most modern focal plane shutters move vertically, as it's a shorter distance, but the original focal plane shutters moved horizontally, presumably because it allows more room for additional mechanism.) The interaction between various laws of physics causes interesting effects.

One of the interesting effects of the dual shutter curtain approach is that the speed the shutter curtains can move determines the width needed between them for a given exposure time which determines the gap that is allowed between the first (front) and second (rear) shutter curtain. That in turn interacts in interesting ways with flash photography, because for certain combinations of speed and gap between the shutter curtains only certain parts of the image may be exposed to the light from the flash. To avoid this the speed needs to be slow enough that the entire image is open to the light at the time the shutter fires so that it all receives the light from the flash. The shutter speeds where this is true are typically much lower than the maximum effective shutter speed (eg, 1/125th or 1/250th of a second in modern focal plane shutter cameras, compared with 1/8000th of a second maximum shutter speed). The timing is called the X-Sync timing, because of the speed with which it can sync with a "X"(enon) (electronic) flash. (There are other traditional flash types and flash sync types, depending on the speed with which the light from the flash peaks and dies away.)

There are other shutter designs, including leaf shutters, made of a pivoting "leaf" over the lens, which can move faster and achieve flash sync at any speed they support (due to them opening them always exposing the entire image at once). However they need to be built into each lens making them more expensive in a system that allows interchangable lenses. And the construction can be more difficult to allow variable shutter speeds. (Apparently disposable cameras are often built with single speed leaf shutters.)

A further wrinkle is that on a modern focal plane shutter, the flash can be synchronised for the opening of the front curtain or the closing of the rear curtain. Rear curtain sync tends to make the final image in any movement more dominant, whereas front curtain sync would tend to make the initial image more dominant.

Still on a photography topic, depth of field (DOF) refers to the portion of the image which is acceptably in focus. "Acceptably in focus" depends on the the intended use of the image, and hence the acceptable size of the circles of confusion. Typically this limit then depends on the ability of the human eye to resolve detail in the intended output size. As a rule of thumb the average person can resolve about 5 lines per mm at a typical close viewing distance, under 0.2mm then it will be perceived as in focus. (Although the maximum limit of the human eye seems to be around one minute of arc, which works out to about 1/16th of a mm at a normal reading distance. Photography usually uses 1/5th of a mm or 1/6th of a mm for calculations though.) These figures are then generally translated with the idea of a normal print size (eg, 5x7" from a 35mm negative), to get the maximum permissible circle of confusion on the negative/digital sensor. (See also sharpness tutorial, which also explains the need for an unsharp mask -- to restore the acutance, edge contrast, of an image. And acutance is also a photography bulletin board.)

The acceptable circles of confusion also feed into the hyperfocal distance, the minimum distance beyond which everything further away is acceptably in focus, where infinity is part of the depth of field. This depends on the apeture size, as well as the focal length, and what "acceptably in focus" means for the particular use. (At the near end, everything from half the hyperfocal distance is also acceptably in focus -- for the same definition of "acceptable".)

And various people have created tables of acceptable circles of confusion based on assumptions about standard image enlargements.