Thoughts on Trailing Curtain Sync

[John Sessoms]

From: mike wilson
> mike wilson wrote:
> 
>> > John Sessoms 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?
>>> >>
>>> >> E.G. like with a radio-sync transmitter or Vivitar 285HV? Dedicated 
>>> >> flash like the AF-540FGZ has its own circuitry to talk to the camera 
>>> >> and can be set to trailing curtain sync.
>>> >>
>>> >> Is this something they could do with a firmware update?
>> > 
>> > 
>> > Non-dedicated flashes fire when they are told to.  It doesn't mstter 
>> > whether that is at the beginning, the end or halfway through exposure. 
>> > On the face of it, some coding telling the camera to fire any connected 
>> > flash at the end of exposure would be a comparatively simple task.  So 
>> > simple that I must go and see if it will work already....
> 
> OK.  With KX and AF280T, it's no go.  Trailing curtain seems to be a 
> PTTL-only mode, as the RTF preflashes.  Some illogicality there...... 
> There is no trailing curtain mode on the DL2.
> 
>> > 

The non-dedicated flash fires when the main hot-shoe contact triggers. 
I'm asking how the camera controls when that main hot-shoe contact 
triggers. Could a camera software change make it trigger the main 
hot-shoe/PC contact on the trailing curtain when the on-board flash is 
set to trailing curtain? Or would it require physical changes to the 
wiring inside the camera?

The K10 and the K20 allow you to set the on-board flash to 
trailing-curtain. The AF-500 (which worked with the *ist-D) and the 
AF-540FGZ have trailing curtain sync built into the flash.

On the K10 and the K20, with the on-board flash set to trailing curtain, 
the main hot-shoe pin triggers on the front curtain. Same for the K20's 
PC sync.

Is this main pin trigger on front curtain hard-wired into the camera, or 
is this something that could be changed by a firm-ware update?