Thoughts on Trailing Curtain Sync

Adam Maas adam at mawz.ca
Fri Jul 2 21:39:21 EDT 2010


On Fri, Jul 2, 2010 at 9:21 PM, paul stenquist <pnstenquist at comcast.net> 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 nc.rr.com> 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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