On Fri, Jul 2, 2010 at 9:21 PM, paul stenquist <pnstenqu...@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 <jsessoms...@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 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
