Thoughts on Trailing Curtain Sync

Godfrey DiGiorgi gdigiorgi at
Sat Jul 3 02:30:58 EDT 2010

All my FourThirds and Micro-FourThirds bodies allow me to enable
second curtain sync any time I want, with any flash. IIRC, both my
Sony R1 and my Canon 10D allowed the same.

The algorithm is very simple: the flash is triggered about 300ms
before the second curtain is released. So it obviously works best with
exposure times of a half second or longer, but then that's when I'd
use second curtain sync anyway.

On Friday, July 2, 2010, Adam Maas <adam at> wrote:
> On Fri, Jul 2, 2010 at 9:21 PM, paul stenquist <pnstenquist at> wrote:
>> On Jul 2, 2010, at 7:05 PM, Adam Maas wrote:
>>> On Fri, Jul 2, 2010 at 4:53 PM, John Sessoms <jsessoms002 at> wrote:
>>>> The K-10D and K-20D both allow you to set the on-board flash to trailing
>>>> curtain sync. How difficult would it be for them to make the hot-shoe also
>>>> fire on the trailing curtain when a non-dedicated "flash" is installed?
>>> Very difficult unless certain assumptions about burn time are made,
>>> which won't be accurate. You need to fire the flash at just about
>>> exactly the burn time before the shutter closes for trailing curtain
>>> to work corectly. Most speedlights have a roughly 1ms full-power burn,
>>> but at low power levels it can be an order of magnitude shorter as
>>> output is normally controlled by burn duration rather than intensity.
>>> Olympus did allow this on some OM models, but it only worked because
>>> of the low sync speed of the camera's (1/60) so that even if the flash
>>> burn time was much shorter than the assumed ~1ms you don't get much
>>> exposure after the burn ends. This doesn't work so well with today's
>>> high sync speeds.
>> Of course you can shoot trailing curtain synch at low shutter speeds on either the K10 or the K20. I get good results shooting trailing synch on the K10, K20 and K7 at 1/8th or 1/15th.
>> Paul
>>> -Adam
> low shutter speeds work better for non-dedicated flash and rear
> curtain sync, it's at high sync speeds where the problem occurs becaue
> the burn time is a much larger portion of the period the shutter is
> open so a short duration burn triggered early nets you mid-curtain
> sync rather than rear-curtain sync. With a dedicated flash it's a
> non-issue because the burn time can be predicted and the flash
> triggered at the right moment so it cuts off just before the shutter
> closes.
> -Adam
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