Focusing in Low Light Underwater

Focusing on light-colored subjects that blend into the water can be difficult, especially in low-light. Your camera needs light and contrast to focus properly.

 

schooling barracuda

Barracuda can be very hard to focus on. Shooting wide angle can make it easier.

 

Here's some tips to help you in this situation:

 

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  • Remember that cameras focus by finding the distance with the largest contrast difference within the focus point. Make sure your camera is trying to focus on an area that has a strong contrast different. For example, red against green, or bright against dark. If your camera is set to "spot focus", than the small focus area in the center of the viewfinder or live view must be over an area with strong contrast.
  • See if your camera has a continuous focus mode, sometime called "AI Servo focus mode". Most dSLR's and some compacts, such as the Canon G10 or the Fuji F10, have this mode. When in this mode, the camera will continually auto-focus, and you can usually press the shutter at any time. If your housing does not have access to this button,
  • Pressing the shutter down half-way will lock focus. If there is a bright, high contrast subject nearby that is the same distance away from what you are trying to shoot, you can lock focus on the high-contrast subject and recompose. Some dSLR housings even have a dedicated focus lock button.
  • A strong focus light will help, but that only works for a short distance away. When shooting with a compact camera, I often bring along a UK light canon, that I can shine on a subject to help the camera achieve focus faster. With practice, you can move the light away from the subject at the last moment to avoid a hot spot.
  • "Spot focus mode", also called center focus mode, often results in the quickest focus lock - but in low light the camera will "hunt" for focus if this focal area is not placed over an area with a minimal amount of contrast. If you are able to move your focal point around, that can also help.

Additional Reading:

 

 

These bumpheads in Bali were far away and hard to focus on. My camera hunted for a while, I should have switched to continuous focus mode. Nikon D80, F9, 1/60th, 60mm lens. Post-processing increased the contrast.