Comments on: Flash sync speeds — Photography podcast #47

By: Turning day into night in photography | Photography podcast blog and forum - Photography.ca

Thu, 03 Mar 2011 23:32:47 +0000

[…] 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 […]

By: Nancy Cuppy

Nancy Cuppy — Sun, 06 Jun 2010 15:42:25 +0000

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

By: David Crowe

David Crowe — Sun, 03 Aug 2008 04:45:05 +0000

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.

By: David Crowe

David Crowe — Sun, 03 Aug 2008 02:16:54 +0000

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.

By: admin

admin — Wed, 23 Jul 2008 14:52:14 +0000

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

By: Benny

Benny — Mon, 14 Jul 2008 20:24:43 +0000

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

By: Ed

Ed — Sat, 12 Jul 2008 22:46:01 +0000

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.