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Underwater Strobe Sync

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Underwater Strobe Sync
« on: 05 / March / 2009, 08:29:40 »
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In order to use an external strobe underwater you must block the light from the camera's strobe and sync the external strobe to the cameras flash.  Since the SD870 has pre-flash most strobes have a mode to not fire on the pre-flash and fire on the true flash.  This results in the camera always using maximum flash, using battery and taking recycle time.  Some strobes will follow the camera's flash but are not able to follow the pre-flash to flash sequence of 50 to 100 ms, because they take longer to recycle.  If say 100 ms could be added to the time from pre-flash to flash the external strobe could follow.  The rusult would be equivalent to increasing the camera's strobe power while maintaining its control.
Another useful method is for the camera to have a slave mode, where the external stobe does all the controlling of stobe duration.  Some stobes have light sensors, others have power controls.  For this mode the camera should not pre-flash and only provide a minimum flash, that would trigger the external strobe.  This results in less battery use and quicker recycle time.  Any soultions?

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Offline PhyrePhoX

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Re: Underwater Strobe Sync
« Reply #1 on: 05 / March / 2009, 08:33:04 »
just disable the preflash. go to overrides and enable "force flash" and set powerlevel to for example 0 (least power, but maybe enough to trigger the external flash).
« Last Edit: 05 / March / 2009, 08:34:35 by PhyrePhoX »

Re: Underwater Strobe Sync
« Reply #2 on: 13 / August / 2013, 01:20:11 »
I use a Powershot S80 in manual exposure mode, slave flash is set to manual at the lowest power setting to save battery power.  My external strobe is an Ikelite SS50 with TTL attached to a special trigger sensor that emulates TTL from strobe to subject.  Slave strobe will not preflash so my dinosaur analog strobe can keep up and flash in time and with enough power when the shutter trips.  The special strobe adapter is Digital Adapter 2 made by Heinrich Weinkamp purchased for $135 from Reef Photo in Florida.

As of CHDK release 1.2.0, I am now attempting to use the AUTO/Program/AV/TV exposure modes now that the manual flash setting can apply to all exposure modes.  The 1st flash/image taken is wasted as the Digital Adapter learns how it should work.  Subsequent shots after (if strobe is not powered off) will fire the external strobe at the correct time when the shutter trips.

My analog strobes are very old but still cost me new $400 for the SS50 and $700 for the SS300, the Digital Adapter for $135 allowed me to reuse them again with a digital camera.  The CHDK Hack has made my UW Photography much more flexible and usable with my Powershot S80.

And of course I got RAW back since my Powershot S80 had it disabled by Canon designers.

 

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