Flash sync speeds — Photography podcast #47

Pho­tog­ra­phy pod­cast #47 talks about flash sync speeds. We talk about what the flash sync speed is (it’s also called x-sync) and how very impor­tant it is espe­cially when you are tak­ing day­light por­traits out­doors. We also talk about high-speed flash sync as well as answer Sergey’s ques­tion about why the high speed flash sync is not work­ing with the trans­mit­ters that he is using.

Links/topics men­tioned in this pod­cast:
My sleepy dog pho­to­graph
Sunny 16 rule
ST-E2 trans­mit­ter
Canon 580 flash series with the OC-E3 off-camera shoe cord

Thanks as always to Benny, Mer­man, Tmat, Yowzah, Tim and Sergey for recent com­ments and sug­ges­tions. We LOVE com­ments and sug­ges­tions so please send more.

You can down­load this pho­tog­ra­phy pod­cast directly by click­ing the pre­ced­ing link or lis­ten to it almost imme­di­ately with the embed­ded player below.


  1. Nancy Cuppy says:

    Great arti­cle, explained so peo­ple new to flash could under­stand. Mr. Crowe, sorry too confusing.

  2. David Crowe says:

    To con­tinue … how could you design a flash that would bypass this restric­tion on the synch speed? Well, let’s say you’re sim­u­lat­ing a shut­ter speed of 1/125 when the shut­ter cur­tain travel speed is 1/60 of a sec­ond. After 1/125 of a sec­ond the first half of the film/sensor will be exposed because the first cur­tain is half way across and the sec­ond hasn’t quite started yet. Flash! Half the film is now exposed. Another 1/125th of a sec­ond and the first cur­tain has fin­ished its tra­verse and the sec­ond cur­tain is now half way across. The other half of the film is now exposed. Flash!
    With this sys­tem, every time you halve the shut­ter speed, you’d dou­ble the num­ber of flashes (and the power con­sump­tion). For 1/4000th of a sec­ond, you’d have to flash 16 times.
    Note another thing, the expo­sure does last 1/60th of a sec­ond, but any one area of the film is only exposed for 1/2, 1/4, 1/8th etc. of that time due to the fact that the shut­ter cur­tains form a nar­rower and nar­rower slit.
    One ques­tion I have Marko is why dig­i­tal cam­eras still need a shut­ter. If they have Live­View why don’t they just start read­ing from the sen­sor when the shut­ter but­ton is pressed, and stop after the desired shut­ter speed? Maybe a dig­i­tal expert can explain this.

  3. David Crowe says:

    Marko; Let’s talk about how shut­ters really work. Your flash sync speed is the “real” speed of the shut­ter, not the “appar­ent” speed. Slower than the synch speed these are the same, faster than the synch speed the “real” speed is the synch speed and the “appar­ent” speed is the dialed in shut­ter speed.
    A tra­di­tional shut­ter is two cur­tains. One is across the film nor­mally, and the other is wound up wait­ing to go. When the shut­ter is pressed, the first cur­tain starts trav­el­ling across the film — always at the SAME speed, not mat­ter what the shut­ter speed is (usu­ally 1/60th of a sec­ond to tra­verse the film). If the shut­ter speed is slower than the film speed the sec­ond cur­tain waits a while, and then trav­els across the film, shut­ting out the light, at the EXACT same speed as the first cur­tain. At the synch speed (e.g. 1/60th) the sec­ond cur­tain starts trav­el­ling as soon as the first one is fin­ished. This is the only time that the entire film is open to the light. This is the moment that the flash MUST fire.
    What about higher shut­ter speeds, say 1/1000th? Well, in this case the shut­ter speed is only sim­u­lated. The sec­ond cur­tain starts trav­el­ling to shut out the light BEFORE the first cur­tain has fin­ished expos­ing the film. For 1/125th of a sec­ond, the sec­ond cur­tain will start when the first is half way across. For 1/250th, when the first cur­tain is only 1/4 of the way across.
    This means that for shut­ter speeds faster than the REAL shut­ter speed of a cam­era, the film is never entirely exposed to the light at any one point in time.
    What this also means is that at any shut­ter speed, one side of the film starts being exposed a lit­tle before the oppo­site side, so a pic­ture is not truly one moment in time, it’s a con­tin­uum although it would be hard to rec­og­nize this phenomena.

  4. admin says:

    Extra info — Some cam­eras can be tricked into exceed­ing their flash sync speeds using Non– TTL flashes. Here’s an exam­ple with the Nikon D70

  5. Benny says:

    Another really good pod­cast and I learned some­thing new. Thank-you SO much for doing these podcasts!

  6. Ed says:

    I love the flash sync spped of cam­eras like the Nikon D40 and older D70 i can use the shut­ter speed at 1000 and still sync up with the flash.
    This is great for out­door flash pho­tos in bright light.


  1. […] 2 tech­niques; using flash and cam­era in man­ual non TTL (Through the lens) mode as well as TTL mode. We also touch on flash sync speeds. This image looks like it was shot in the late after­noon but it was shot at 1pm. Cam­era mode was […]

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