dual strobes and Canon ettl-II

Hello all. I have searched the forums at Wetpixel as well as other UW Photo forums for the answer to this question, to no avail. I have been using a Canon 20D digicam with Ikelite DS-125. I want to add a second strobe, probably a DS-50. I have been using the single strobe setup to give some sidelight to fish portraits, but want the 2nd strobe to lighten the shadows produced by the single strobe setup. I usually use a manual camera setting with the DS-125 set to ETTL. What is the best way to use the second strobe so that the shadows are maintained, just lightened. I am trying to avoid the flat lighting effect that a dual strobe setup often produces. Should I use the dual synch cord, or use the slave controller on the DS-50. How can I then set lighting ratios between left and right flash (DS-125 on right and DS-50 on the left).

I know how to do this on land with my camera, usimg the dedicated Canon speedlights, but as I am relatively new to UW photography, I would like to take advantage of others suggestions and experience. When buying the DS-50, should I buy the slave or just buy the dual synch cord?

Thanks for all responses and advice, and a Merry Christmas and Happy New Year to all.

Ed

Hi Ed,

The easiest way is to use a strong diffuser on one of the strobes. You're basically setting flash compensation for that flash.

Cheers

James

Won't the ETTL circuitry just give more power to the flash, negating the effect of the diffuser?

Ed

"Ratio lighting" by using different flash to subject distance for the two strobes..........?

The ttl in the camera just turns off both flashes when it think that enough light has come in. It doesn't know where the light is coming from.

So using diffusers, or pulling one strobe back like Ike reminded me will work for ratio lighting. Each foot you pull it back is roughly one stop.

Cheers

James

Maybe I'm still missing something with your explanations - both from Ike and James. If the right hand strobe, the DS 50, is connected by the dual sync cord, and both flashes are set to ETTL, won't they both produce sufficient light so the camera meter is happy that there is a well-exposed image. By moving the secondary flash back or by putting a diffuser on it, won't the ETTL algorhythm just increase the output so it balances the light output of the primary strobe.

Canon ETTL II circuitry on land uses a master and slave approach, where the master strobe sets the lighting ration as 1:1, 2:1, 3:1, etc between master and slave. I guess I'm asking is this possible with the Ikelite system when both strobes are set to ETTL and firing from the dual sync to the housing ETTL circuitry. Again, basic question is how to buy the DS50, with a dual sync cord or with a slave controller.

Ed

You are giving the camera too much credit. The camera has no clue where the light is coming from. All fashes will fire for the same ammout of time. If you put a diffuser on one fash the camera will compenste by increasing the power of both/all flashes. Thus the one without the diffuser will be putting out more light.

Again, basic question is how to buy the DS50, with a dual sync cord or with a slave controller.

There really is no right answer to this question. I'd buy the dual sync cord.

That's the setup I'm currently using, and I'm happy with the way the diffuser on the DS-50 works to push some light into the shadows.

But if you want the most control, the manual controller slave unit would be the way to go, it gives you 10 settings (I think) and a 5 stop exposure range ( I think). The stats could be found for sure on the Ike website.

Good luck with the decision.

Mike

Mike, thanks for your reply. It sounds like you are using the same setup I am planning.

Ed

Hi,

I've 2 x DS-125s with a dual sync cord, and was wondering if the following would be possible:

Primary Strobe set to ttl

Secondary strobe set to 1/4 power or similar.

I would have thought that in this situation the sync chord provide the trigger, and the camera would default to the manual power setting.

I've not tested if this would work, but maybe somebody else can offer some wisdom.

damien