[Coral-List] Optimal lighting for video transect work

[Simon Hartley]

Hi Folks,  

I'm doing postgrad work looking at marine benthic communities at Julian Rock, in the Cape Byron Marine Park northern New South Wales (Australia).  I apologise for jumping in without a proper introduction but hoping to get out in the field again next week and looking for some timely advice.  

I'm looking at building a frame to fit some video lights to an Ikelite housing for video transect work.  The reason for not using regular mounting arms is that I want the lights in a fixed position which is optimal for survey work so I get consistent results in all lighting conditions.  So far I have used a red filter but this is less than ideal, when vis is poor the image is quite green.  Details of the camera and lights are as follows...

	Sony TRV22E miniDV digital video camera

	Ikelite underwater housing

	Halcyon dual 24 watt HID video lights with 9 amp battery canister (I have some flexibility in how I set this up could use just one light or possibly a 24 and 10 watt light instead (would just need to change the cable on my 10watt HID and fit a video reflector))

I'm seeking advice on the best way to setup lights for optimal image quality (to facilitate identification of different benthic categories).  The camera is generally held about 40cm from the bottom while videoing underwater transects on rocky reef.  My study site is a subtropical/temperate rocky reef habitat with a range of corals, algae, sponges and ascidians.  The advice I've had sofar is that two powerful lights positioned on either side of the camera (a typical configuration) would flatten the image at such close quaters and make later analysis difficult.  One suggestion is to set one light well back from the subject and have a second (possibly less powerful light) a little closer on the same side of the camera, to soften any shadows.  This seems to make sense although I wonder if the less powerful light mightn't be more effective on the opposite side of the camera.  Alternatively both 24watt lights could be mounted on the same side and a short distance apart or just one light could be used (this would extend burn time but this is not really a problem as I record continuously pretty much until tape runs out, also may produce quite harsh shadows).  Also there is the matter of whether the light/s are infront of the camera, to the side or behind and how far the lights should be from the subject.  

FWIW 24watt HID lights are roughly equvalent to 100 watt halogen lights in output (10 watt is similar to a 50 watt halogen).  Any advice greatly appreciated.

Simon

Simon Hartley
Associate Lecturer
Master of Science candidate (marine benthic community structure - Julian Rocks)
School of Environmental Science and Management
Southern Cross University

Ph: (02) 66203251
Web: http://www.scu.edu.au/schools/esm/staff/pages/shartley/

Study Environmental Science at Southern Cross University http://www.scu.edu.au/schools/esm/

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