Can someone explain 'Flash Sync" please

Discussion in 'Beyond the Basics' started by RickyN29, Nov 19, 2005.

  1. RickyN29

    RickyN29 TPF Noob!

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    I would like a better understanding of flash sync speed and it's effect on photographs.

    On my 350D, the flash sync is supposedly max 1/400sec. Yet, on the 430ex Speedlight, I can select High Speed Flash Sync and it will work up to 1/4000sec. But what does this all mean anyways.

    I am a little confused. So any input would be appreciated.
     
  2. hobbes28

    hobbes28 Incredible Supporting Member

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    Flash sync is how fast of a shutter you can shoot with and have it still be open when the flash fires. What it means is that you can shoot up to a 1/400 shutter speed and be assured that the flash will fire in that span of time. Once you get over that speed, there is no guarantee that the flash will be lit while the shutter is open. Generally, a flash lasts for 1/700 of a second so I would think that the high speed sync just tries to fire the flash that critical microsecond before the shutter opens and make the flash overlap the shutter.

    Hope I didn't confuse you more. :D
     
  3. will turner

    will turner TPF Noob!

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    the effect on photos is that not all of the photo will be lit, only half or with some higher shutter speeds mabey even none. i think this is because the flash has allready triggered before the shutter is fully open, creating the only half lit photo.
     
  4. jadin

    jadin The Mad Hatter

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    Sounds like the 430ex has "better" electronics and has much better timing than an ordinary flash.

    Test it out and see just how much better. :)
     
  5. RickyN29

    RickyN29 TPF Noob!

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    Thanks for the replies everyone. Yeah, see that is what I thought, but then I have read some threads regarding say, Nikon Vs Canon and how the flash sync speeds were like 1/500 and 1/250 max. I bought the 430ex, a relatively new speedlite to the market (as far as I was told). And the manual clearly states that you can put it to highspeed sync and it will sync to 1/4000 sec. I have a tried it out a few times with incredibly fast moving items and it does in fact freeze motion and light the whole scene. So I guess it is just pretty nifty. The camera manual, and the flash manual really contradicted each other.

    And yeah, how it can fire a preflash for exposure comp, and fire a main flash all within 1/4000sec is absolutely beyond me!

    Thanks again
     
  6. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    The sync speed of a camera has to do with the shutter...typical focal plane shutters open in two parts. At higher shutter speeds, the time when both parts are open, is very very quick...or maybe even not at all. The flash has to fire when both parts are open, or it won't expose the whole image.

    High-speed sync is a neat feature. From what I understand, the flash unit fires many small, very quick bursts of light that add up to the correct exposure. So if a part of the shutter is not open for some of the flashes, it will be open for the others.

    The trade of is power. Using high speed sync really limits the distance at which you can use the flash effectively. Probably uses up battery power faster as well.
     

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