John Sessoms wrote: > From: "Bob Blakely" > >> I'm curious. What can the flash know of rear curtain sync timing save >> that given it by the camera's shutter? If nothing, what's to set on >> the flash? What difference could it possibly make? > > > This is just a guess, but I know the AF-500FTZ has a switch position for > rear curtain sync. > > What I think is somewhere in Pentax's dedicated flash connection, > there's a pin that gets a signal (V+ or ground??) when the shutter > curtain opens and loses that signal when the rear curtain starts to > close. Say something like this: > > Curtain Curtain > |Opens |Closes > __------------___________ V+ > > OR > > --____________----------- ground > > It'd be easy to build a trigger circuit to detect the state changes and > switch the flash trigger to either the leading edge change or the > trailing edge change. > > Thinking about it now, a standard hot shoe could just go to ground for > the duration of the curtain being open, so you don't even need the > dedicated pin to trigger rear curtain sync; just design your rear > curtain trigger circuit so it will flash when the ground circuit opens > again. > > For a lark, I tried the AF-500FTZ with a K-1000, and it doesn't do rear > curtain sync even with the flash switch set in rear curtain position, so > I think Pentax does use a dedicated pin. > > And, I'll bet it's the 4th pin in approximately the 2 o'clock position > that permits rear curtain sync, since Pentax had TTL Auto-flash with the > LX and Super Program and AF-280T, which I'm pretty sure uses the two > additional pins at 5 o'clock and 7 o'clock. > > The AF-500FTZ manual says rear curtain sync only works with the PZ-1 > [PZ-1P], which I expect was the only camera with that 4th dedicated pin > at the time the manual was written, because AF-500FTZ rear curtain sync > does also work with the *ist-D. >
The extra pin is the digital signal pin, it allows full communications between the flash and body, more than just the analog quench indication and flash status indication that the older analog 3-pin(really 4) TTL system supports. -Adam -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
