Technical Question: Flash and shutter speed

[JimmyMelbourne]

Gday all,

This may be a dumb question, but why on DSLRs are flash shutter speeds limited to 1/160 second? This is the case on my A300 and was just wondering what the physics is behind this. A link to a good informative website might suffice.

Thanks

 

[winono]

Hi,

maybe this article can be useful:
http://www.kenrockwell.com/tech/syncspeed.htm

 

[Leon van Roosmalen]

The time the flash fires can be as short as 1/10000 of a sec. and to lighten the scene the shutter of the camera has to be open completly.

A standard shutter can be seen as a slit that moves in front of the sensor. The lower the shutter speed the wider the slit so the more light reaches the sensor.

At speeds slower then the sync speed the slit is as wide as the sensor so therefore even with a flash time of 1/10000 of a sec. the whole sensor gets light at the same time.

If you use a HSS capable flash it sends out a burst of short flashes during the movement of the slit to lighten the complete scene.

Hope this helps.

Greetings Leon.
--
http://www.leonvanroosmalen.nl/

 

[wdenies]

Mechanical focal plane shutter. The shutter has to be wide open when flash fires. This is guarantied up to a max. speed (in your case 1/160).
Shooting at a higher speed will result in a partly exposed picture.

Most P&S (and some dSLRs -D70) have an electronic shutter - no moving mechanical parts- to overcome this problem, but other disadvantages are introduced.
The best:

• lenses with built-in leave shutter: flash sync at any shutterspeed

Wim

 

[Dave_Anderson]

I googled up a page that illustrates the issue:

http://mir.com.my/rb/photography/fototech/focalplane/

If your camera, with the right flash, will support HSS, then you can have the flash work at any shutter speed. What HSS does is provide flash illumination for long enough or the "traveling slit" to cross the entire imaging area(sensor or film) by providing a rapid series of bursts that are seen by the sensor as one very long burst.

 

[WaltKnapp]

The best:

• lenses with built-in leave shutter: flash sync at any shutterspeed

Well, except those shutters don't go to all that high a shutter speed anyway.

Oh, and the other thing, electronic flash can be much faster than 1/10000 sec. My Minolta 1200 ringflash does up to 1/56000 sec, maybe a bit more. A lot of macro flashes are able to do very fast flashes as motion is harder to stop at high macro. It's one of the things that makes the better ones so costly.

Walt

 

[JimmyMelbourne]

Thanks for the answers guys, makes a lot of sense now.

 

[jrfarrar]

There is a really great VISUAL of this in the following video:

http://www.youtube.com/user/snapfactory#play/all/BC5A73FEA8B7D7D2-all/0/Xnn5nzPvoIM

Best explination I've seen and have passed it on to a lot of people. If you have no patience skip to the 1:00minute mark. Although the first minute asks your question essentially.