Seacam Seaflash 150 - First Tests of Rear Curtain Synch with Canon

E-TTL - #1



MANUAL BRACKETS - Full, 1/2, 1/4, 1/8 power - #2


MOTORDRIVE - #3


REAR CURTAIN SYNCH - #4

Canon shooters have long been challenged in the underwater realm when trying to achieve rear curtain synch. The issue is that only Canon topside E-TTL enabled strobes would work in rear curtain synch mode. Manual strobes, like we are used to using underwater, did not. That was an advantage that Nikon had over Canon when shooting ultra slow shutter speeds and trying to convey a sense of motion. With Nikon the trail of action would be behind, but with Canon (and forced front-curtain synch) the motion would be in front of the subject, and therefore visually confusing.

Seacam now has developed rear curtain synchronization (RCS) with their Seaflash 150. With a new hardware upgrade introduced in March of 2009, RCS is now possible with both the MKIII and 5DII Canon cameras. New strobes delivered after that date will have the new technology integrated, those already in the field will need to go back to Seacam from an update in the electronics. Having TTL exposure automation PLUS rear curtain synch is an exciting new technology. For me, as a Canon shooter anyway.

* To set 2nd curtain synch (Rear curtain), go to the custom functions menu on Canon cameras:

Canon MKIII - Function Bank II, category 5, choice #1 for 2nd curtain

Canon 5DII - Flash has to be attached to camera and turned on. Menu 3rd from right that looks like a wrench. Go to: External speedlight control > Flash Function settings > Shutter synch > 2nd curtain. Unless camera senses speedlight with 5DII, it can't be done.


Just set it and leave camera in 2nd curtain synch always. If using a fast shutter speed it does not matter, and if using a slow shutter speed you’ll want it. SHOT #4

Also, nice to know it is extremely consistent for action sequences, as we can see from this series of 37 photos shot on motordrive at F-2.8 and using only 4% of the power of the strobe for each shot. Photo shot from behind strobe, focused on LED on rear of strobe, but showing consistency of light emitted from strobe to the exposure slate. You probably can't see it in this small screen grab, but each LED reads "4", without variation. A smaller aperture would have used a higher percentage of strobe power, but this LED graphic makes it very easy to choose the correct aperture for whatever the strobe-to-subject distance might be to assure ultra-quick recycle when shooting motordrive sequences SHOT #3

While I was at it, I also tested the E-TTL, but I'd done that before so no surprise it was very accurate. See the range of exposures from F-4 - F-22, F-22 being a little dark only because it exhausted all the power in the strobe at the minimum F-stop. BTW ... when it dumps full power the LED display reads EE, and it emits an audible signal so you know, even without looking. SHOT #1

And finally, here is the test of the manual brackets at full power, half power, quarter power, and one-eighth power; each with about 6/10ths of a second between shots. This was as quickly as we could rotate the aperture dial on camera and on slate. The recycle was actually much quicker at settings less than full power, too fast for me to actually time. Testing did demonstrate extremely rapid recycle capability. SHOT #2

Seaflash 150 works with Canon (E-TTL) and Nikon (I-TTL).