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.
Randy Aldrich 
Your link has an extra http son.
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Fixed. Thanks son.
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Thanks for the link, Randy.
You’ll often see that “leaning” effect in photos from cell phone cameras even today, because they use a slow “rolling” electronic shutter that produces the same effect. Here’s an example from my cheapie LG phone.
As I noted in my original article, I was really talking about DSLR cameras, since most point-and-shoot models use a purely electronic shutter (i.e. the sensor turns on and off), without the old mechanical blades. Interestingly, though, some DSLRs (such as the Nikon D40) have a hybrid shutter that has a relatively slow mechanical set of blades, as well as a sensor that can turn on and off more quickly.
So the D40 (and my D50) has a 1/500th flash sync speed using the hybrid shutter, while even the super-high-end D3 and D3x have a slower sync speed, because their higher-resolution, better-performing sensors don’t allow for electronic shutter behaviour, and must rely on the physical limits of their shutter curtains instead.
I didn’t understand this stuff at all until I decided to write the article, by the way. It’s a good way to learn things.
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Derek, Thanks for stopping by!
It’s funny you mention the cell phone thing. Just after I posted this I realized this is likely why I get strange shapes from my iPhone camera. I don’t think it has a physical shutter, probably just a very slow rolling sample of the sensor which has the same effect. Something I’ll look up later. In either case, check out a quick sample I just posted:
Thanks for the tip on the difference between the DSLR shutters and the P&S shutters (or lack there of). I knew the difference but made an assumption that others would too that I shouldn’t have. I’ll correct it.
Thanks again for stopping by!
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