In photography, shutter lag is the delay between triggering the shutter and when the photograph is actually recorded. This is a common problem in the photography of fast-moving objects or people in motion. The term narrowly refers only to shutter effects, but more broadly refers to all lag between when the shutter button is pressed and when the photo is taken, including metering and focus lag.
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Film cameras
In film cameras, the delay is caused by the mechanism inside the camera that opens the shutter, exposing the film. Because the process is mechanical, however, and relatively brief, shutter lag in film cameras is often only noticeable (and of any concern) to professionals. SLRs have slightly longer shutter lag than rangefinders, because of the need to lift the mirror. Point and shoot film cameras often have significant shutter lag.
Digital cameras
Shutter lag is much more of a problem with digital cameras. Here, the delay results from the charging of the CCD and relatively slow transmission of its capture data to the circuitry of the camera for processing and storage. Recent improvements in technology, however, such as the speed, bandwidth and power consumption of processor chips and memory, as well as CCD technology, have made shutter lag less of a problem. As of 2007, the greatest advancements have been limited mostly to professional, "prosumer," and high-end consumer-grade digital cameras. Inexpensive (most "point-and-shoot") digital cameras, however, have even reduced the average shutter lag to half seconds, and higher-end "point-and-shoot" cameras have reduced this down to a quarter second or less.
AE & AF lag
However, what many people consider shutter lag is in fact the time the camera takes to meter (set the exposure) and auto-focus, which is lag of a different cause but similar effect.
These causes of lag can be eliminated by pre-setting the exposure and focus, by either manually setting the exposure and focus, or by pre-exposing and pre-focusing. Pre-exposing and pre-focusing mean "using automatic exposure and autofocus, then fixing the settings so they do not change"; this can often be done by holding the shutter release halfway down, or by using a separate "AE / AF lock" button (useful if taking multiple photographs that are not in a burst), and means the subsequent photographs will be taken faster. These techniques can be combined – one can manually set the exposure and then use AF lock or conversely.