Selecting an Underwater Focus Light

SeaLife Staff

Auto focus lenses are a feature of many digital cameras, and require sufficient ambient illumination and good contrast for the camera can “see” the subject and focus accurately.  When shooting in wrecks, caves or at night, a focus light is critical for the camera to focus.  Even when diving in bright lighting conditions and clear visibility, you may find yourself shooting on the shadow-side of a reef where lighting conditions are less than optimal.  Regardless of your underwater shooting conditions, a good focus light is an essential accessory that belongs in every underwater photographer’s gear bag.

The SeaLife DC2000 is an underwater auto focus camera.

Note: If you are shooting with a fixed-focus camera or photo-video lights, then you don’t need a focus light.  A fixed focus lens does not adjust so everything beyond the camera’s specific shooting distance will be in focus.  If you are shooting with one or more photo-video lights, these lights will serve as the image illumination function.  If you are shooting with one or two strobes, a good focus light becomes important.

There are several options to consider when selecting an underwater focus light – lumens, beam angle, mounting location and special features, like flash detection.

A good focus light should have at least 600 lumens for a narrow spot beam and 1200+ lumens for wide beam angles.  A narrow, spot beam light aimed at the middle of the image frame is acceptable because most digital cameras give more weight to the center of the field-of-view. I wider beam angle is desirable because you get the additional benefit of seeing the entire image field clearly and composing the shot. A wider beam angle spreads out the light, so a higher lumen light becomes necessary to properly illuminate the subject.

Sea Dragon Flood and Spot beam underwater LED lights from SeaLife

The ideal mounting location for a focus light is on the camera housing’s cold shoe, which is usually positioned right over the lens.  Make sure the focus light you select has a cold shoe mounting accessory available that fits your camera housing.  For example, the Sea Dragon lights use the Flex-Connect Cold Shoe Mount fits all underwater housings with a cold shoe.

Mounting a focus light on the Cold shoe of your underwater housing

Mounting the focus light over the lens does introduce “backscatter” (those white spots that show up in the picture that occur when the light reflects off the particles suspended in the water).  The best way to eliminate the backscatter effect is to select an underwater light with flash or strobe detection feature;  the “flash detect” will power off the light for about 1 second when the strobe fires.  For example, the Sea Dragon 2300 Auto, 3000 Auto or 4500 Auto lights all include a light sensor and the flash detect feature.  Another option to minimizing backscatter is to shoot in manual mode and set camera to darker exposure, like f/8, 1/125sec and ISO 125.  Increase the strobe brightness to compensate for the camera’s darker exposure setting.  The strobes will overpower the focus light so it becomes “invisible” and only the strobe’s light will be captured. 

If you have experienced out-of-focus shots with your auto focus camera, seriously consider adding a focus light to your toolbox.

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