From: Thibouille
I don't think so but would a K7 sync on 2nd curtain when used with
X-sync cord (or hotshoe but not with a Pentax flash)?
Or should I trick the Studio flash with pentax flash to fire them ?
I can't test just yet and I'm curious ...
I think the K7 works the same as the K10 & K20.
The K10 & K20 do rear curtain sync with the pop-up flash, but there is a
pre-flash with the front curtain that will fool an optical slave.
If there's a way to turn the pre-flash off when using the pop-up flash,
I have not found it. I've gone through the manual diligently.
They won't do rear curtain sync with a hotshoe mounted flash except for
the AF-360FGZ and AF-540FGZ, both of which also have pre-flash on the
front curtain.
The K10 doesn't have an X-sync (PC) socket.
The K20 manual seems to indicate you can have rear curtain sync through
the X-sync (PC) socket, but it still has the front curtain pre-flash
when I tested it.
I tested using a CyberSync connected to the PC and a Vivitar 285HV set
to 1/16 power on a Quantum Battery One to get a really fast recycle time.
I couldn't get a "rear curtain sync" flash off the PC with a shutter
speed faster than 10 sec.
And with a 30 sec exposure I got 4 flashes. I think the K20 just closes
the X-sync (PC) circuit and leaves it closed until the rear curtain
starts to close. So, what I'm seeing is the CyberSync transmitter's
re-cycle time instead of the rear curtain sync. I get another flash
about every 8 seconds.
If it is just flashing every 8 seconds when the CyberSync recycles, I
should get another flash at 32 seconds if I use Bulb ... and lo & behold
it comes in right on schedule at 34 seconds.
If you had a circuit that would trigger the flash when the X-sync (PC)
socket circuit opens you could probably get rear curtain sync with the
X-sync. I don't know how to build one, and I don't know where to buy
one, but now I know what to look for.
I don't know if the K7 works any differently than the K20.
Both manuals (K20 & K7) have the same statement regarding rear curtain
sync with the X-sync (PC) socket:
"To prevent vignetting caused from Trailing Curtain sync, it is
recommended to take a test shot using a shutter speed one level slower
than the flash sync speed."
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