Shutter Speed Calculator

Shutter speed controls how long a camera sensor or film receives light. Together with aperture and ISO, it forms the exposure triangle. A longer exposure gathers more light and records more motion blur, while a shorter exposure gathers less light and freezes movement. This calculator finds the exposure time that matches a selected aperture, sensitivity, and measured scene brightness expressed as EV100. Exposure value is a base-two scale. At ISO 100, EV 15 represents bright sunlight, EV 12 is typical open shade, and lower values describe progressively darker scenes. Increasing EV by one means the scene is twice as bright and requires half as much exposure. The core equation at ISO 100 is time equals aperture squared divided by two raised to EV. Sensitivity modifies that time inversely, so ISO 200 needs half the exposure of ISO 100 when aperture and scene light remain unchanged. The result is shown both as exact seconds and as a familiar reciprocal shutter notation. For example, f/8 at ISO 100 and EV 15 produces 0.001953 seconds, which is approximately 1/512 second. Cameras offer standardized shutter steps, so the nearest selectable setting may be 1/500 second. Small differences are normally handled by choosing the closest setting, adjusting aperture or ISO, or using exposure compensation after checking the meter and histogram. EV100 should describe the actual scene rather than a desired camera setting. A handheld light meter, camera meter, or reliable lighting reference can provide it. Reflected-light readings can be influenced by unusually bright or dark subjects, while incident meters measure the light falling on the subject. Long exposures may also require reciprocity-failure corrections for film, and filters reduce transmitted light unless their effect is already included in the measured EV. Use the calculator when planning studio lighting, landscapes, night photography, motion effects, or equivalent exposures. A fast shutter is often preferred for sports and wildlife, while slow speeds create smooth water, light trails, and intentional blur. The mathematically correct exposure is only a starting point: subject movement, focal length, stabilization, noise, depth of field, dynamic range, and creative intent all influence the setting a photographer ultimately chooses.