, the shutter
is the part of the camera
that controls for how much time the film
is exposed to light
The only cameras that do not need a shutter are digital cameras (they simply turn on the CCD when necessary), and pinhole cameras (exposure times are so long that you can use a hat or a hand as a shutter).
Shutter characteristics are:
- Its exposure range, that's to say, the distance between the minimum and the maximum exposure time.
- Its precision and repeatibility.
- Its lag, that's to say, the time (usually measured in milliseconds) between the moment you actuate the shutter, and the moment it actually starts to open.
- Its step, that's to say how small the step between the times it can deliver. A mechanical shutter usually works by factors of two: one second, one half, one quarter, one eigth... Electronic shutters can be controlled with great precision, and they can be nearly continuous. In practice, they typically have a step of 1/3 of an f-stop
Shutter can be mechanical
. The mechanic kind uses springs, levers and gears, and it is normally limited to the range from 1 second to the thousandth of a second.
Electronic shutters can go from 1/8000 (the eight-thousandth fraction of a second, or 0.125 milliseconds) to many minutes (the upper bound is battery
Some electronic shutters (for example, the one on the Nikon FE
) have a "fallback
" mechanical time, to allow you a modicum
of function even without batteries.
Mechanical shutters obviously don't die on you when the batteries end, but this is less of an argument now that modern cameras are completely slave to the batteries (most modern SLRs cannot even advance film without batteries).
Shutters can be further divided into leaf shutters and focal plane shutters.
Relevant writeups: synchro X, B, T, shutter speed.