Reading path: Underwater images and evidence →

Start with shutter speed

Shutter speed controls how long the sensor records movement. A faster exposure can make a fin, drifting larva, or swaying tentacle look sharper, though no single speed suits every subject. A slow-moving colony may tolerate a longer exposure; a fish crossing the frame needs a shorter one. Begin by choosing a speed that matches the motion you see, then review the image at magnification. If the subject is still blurred, increase the speed or wait for a pause in its movement.

Balance light and depth of field

A faster shutter admits less light, so the rest of the exposure must compensate. Opening the aperture lets in more light but reduces depth of field, which can make a close organism's features fall outside the sharp plane. Raising ISO increases sensor sensitivity but can add visible noise, especially in dark water and shadowed backgrounds. Make one change at a time where practical. For a small drifting subject, a moderate aperture and a carefully raised ISO may be a better compromise than an extremely shallow focus plane.

Add light when it is appropriate

A strobe or video light can provide illumination, but it must be positioned and used with care. A brief strobe pulse can help render motion crisply when the ambient exposure and camera settings are suitable. Artificial light also changes color and may disturb sensitive animals, so consider the subject and local guidance. Avoid blasting a subject repeatedly just to improve a frame. If you are using ambient light alone, prioritize a stable position, brighter conditions, and a composition that keeps the subject against a less distracting background.

Use an example and keep notes

Suppose a small fish is moving through a shaded kelp holdfast. If the first photograph shows a blurred body, shorten the shutter time, then check whether the image became too dark. Open the aperture slightly or raise ISO in a modest step, and inspect both sharpness and noise. If the eye is sharp but the tail is not, that may reflect depth of field rather than motion. Record the settings that worked in similar conditions. A small set of deliberate adjustments is easier to learn from than changing everything between frames.

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