lightning for shooting shark

Hi all.

First of all, sorry for my poor english as I'm not fluent speaker. I'm going on a liveabord in Egypt to take pictures of sharks in october. For my usual dives, I uses 2 backscatter macro wide lights. I also have a Backscatter mini flash. I'm afraid to scare sharks with the torchlights so they don't approach. But As I have only one strobe, I'm afraid too to not have enough light with it !

What would you choose ?

Thanks

Lights are nowhere near as powerful as flash, they can work for macro as you are so much closer, but you are quite a distance from the sharks in many circumstances, so even is the lights had no impact on shark behaviour, they are not going to have enough power to provide significant illumination on the sharks.  The Mini flash while it has more power is relatively low in power as far as flashes go.

What camera are you using?  The f stop is the parameter that impacts flash exposure and smaller sensor cameras can use wider apertures, so whether it is adequate will depend upon the camera/lens you plan to use.

Hi Chris

I have an Olympus EM5 MKiii and an Olympus 12-40 f2.8. I know it's far to be a very sensitive sensor. 

You would probably get away with f4.5 - 5.6 range particularly shooting in the blue where corner performance is not so important.  The sensitivity of the sensor is not the issue - the smaller sensor does not need the lens stopped down so much to get good corners.  m43 can use f8, APS-C f11-13 and full frame f11-16.   So with you m43 sensor you can open up the aperture more. 

I would look at using the single mini-flash  and shooting at the f4.5-5.6 range, normally for sharks you pull the flash power back a little to avoid blowing out the undersides.  Shoot in RAW and be prepared to tweak the colour balance in post processing.  Be sure to adjust your shutter speed and ISO to not over expose ambient light. 

Basically without the flash you want to get a good deep blue from your exposures so set an aperture in the range f4.5 -5.6, ISO at 200 to start and adjust the shutter speed (within limits of flash sync) to get a good BG blue.  Then use that shutter speed when shooting with the strobe.  You may find f4.5 a bit too bright, so if need be stop down till you can get the required exposure without exceeding your sync speed.

Thanks a lot Chris ! Priceless explanation ... I'm more a macro guy because there is no big fish where I live. So that's new for me.

Would suggest you don't let your creativity be limited by a strobe. Plan some ambient light shots too as the Oceanic White Tips that you will presumably be shooting are often in shallow, and very clear water.  Shoot with the sun behind, with manual white balance, at about 5m and you can get some beautiful head on shots.  if you shoot into the sun, you will need a flash, or go under the shark and shoot silhouettes.  Bear in mind they are inquisitive and will very likely come and check you out, coming right up to your dome.  Listen to the guides, too - they really know how to get a good and safe encounter.  

Hammerheads will be in deeper water (30m+) and your strobe is unlikely to be enough to light it (if indeed your guide allows their use in case it spooks the shark and ruins the experience for the group).  They are a bit more shy, and less likely to come close - unless you are really lucky. So ambient can work well here too. 

Maybe try and work different angles (hammerheads from above in an S-shape  work well) and think about putting manual white balance to one of the function buttons so you can adjust it easily?