Help with Underwater System Setup

Hi everybody,

I would like to ask some help in the following matter: My girlfriend is doing her masters into aquatic bottom vegetation, and she is trying to develop a system to photograph the bottom. The system consists into a frame , to which a Canon S2IS + Ikelite housing is attached:

http://img56.imageshack.us/img56/4341/came...memediumwa8.jpg

However, she is having problems with illumination, since her subject is lake bottom, where water is darker. By using only the camera's flash, this is the kind of images she gets:

http://img62.imageshack.us/img62/2624/macr...22mediumll9.jpg

http://img259.imageshack.us/img259/6789/ma...24mediumkq5.jpg

So, my two questions are:

1) What is the best way to get the camera to focus on the bottom, instead of the suspended matter? I've tried manual focus, but it is hard to tell due to the small LCD. The camera is at approximately 1 meter from the bottom. Could I use a smaller aperture in order to get deeper Depth of Field and keep everything in focus?

2) The most important: How to properly light up the bottom? She is in doubt between getting strong flashlights or getting an underwater flash strobe. Her worry with the latter is the reflection of the flash by the suspended particles. Any advice on the best lighting scheme would be most valuable.

Thanks,

Thiago Silva

Thiago,

I may be very wrong, but to me it looks like there is stuff growing on, or in contact with the housing lens port.

At a guess I would have thought the two torches you have mounted would have been ample to have the camera focus lock on the bottom.

From your two pictures, it almost looks like the a dark sandy bottom is in focus, yet the green week is so near that it is obscuring the view of the bottom.

If however the water is simply that dense with vegetation that you cannot even see the bottom, then you've a greater problem.

Using torches will have the advantage of lighting the bottom to aid the camera in focusing. My doubt would be are they bright enough to light the subject without the internal flash. Since you already have two torches mounted have you tried taking a shot with the strobe turned off?

Regardless of whether you use torches or external strobes to light the subject the important point is the angle at which the light strikes the subject. The position of the two torches you have mounted doesn't look too bad. Alternative positions with strobes or brighter torches are a bit lower on the frame so that the light comes in from more of an angle from the side or higher on the frame just higher than the camera with the lights pointing straight down or even slightly outwards so that the sobject is light by the overlapping edges of the beams rather than the centre of the beams. This way the suspended matter will be less well lit and show up less.