I’ve been reading Derek Miller’s blog for a while now and I love his Camera Works series.  Most of the stuff he posts in the series I already have a pretty good handle on but he does an excellent job describing (and simplifying) exactly how Cameras (and photography) work. Back in September he posted an article about Shutters, Flashes and Sync Speed.  Although I have a general knowledge of how all 3 work Derek provided a great in-depth write-up.  I have no idea how I missed it before but I read it today and it’s fantastic!

One key idea I’ve never really understood is how camera’s overcome their technical (mechanical) limitation on shutter speed.  Derek provides exactly the write-up I needed.  Essentially they don’t, they just use 2 shutters at the same time (both moving in the same direction) to allow a ‘slit’ of light through rather than expose the entire frame/sensor at a time.

If a subject is moving fast enough and the slit is moving slow enough, this can result in some interesting photographs, like this famous 1913 Photograph by Jacques-Henri Lartigue.

As Derek writes, this is an exaggerated effect and will most likely never be so dramatic with today’s cameras DSLRs without something moving at extreme super-sonic speeds.

Please visit Derek’s site for the full write-up.

EDIT: Derek was kind enough to stop by and suggest that this discussion really only applies to DSLRs (or Film Cameras ::Gasp::) since they’re the only ones with mechanical shutters.  Most (if not all) point & shoot cameras (including your cell-phone cameras) simply turn the sensor on and off.  Some of these electronic means of exposing the sensor even go slow enough to produce the same effect.  See the background of the following photo shot with my iPhone:

Each one of those slanted boxes should be a perfect rectangle.