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.
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Great article, explained so people new to flash could understand. Mr. Crowe, sorry too confusing.
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.
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.
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
http://strobist.blogspot.com/2007/05/hacking-your-cameras-sync-speed-pt-1.html
Another really good podcast and I learned something new. Thank-you SO much for doing these podcasts!
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.