Exposure Time

Shutter speeds are a critical factor when choosing a security camera, especially for environments with low light levels. Also known as exposure time, the camera’s shutter speed controls the amount of light allowed to fall on the image sensor. Low light conditions require slower shutter speeds in order to capture useable images. While slow shutter speeds are fine for monitoring stationary objects, this can can render security cameras useless if the required exposure results in blurred objects in motion.

While most security camera manufacturers often include minimum illumination in their specifications, they often omit the shutter speed needed to obtain the image at that light level. Mobotix is one IP security camera manufacturer which includes the shutter speed with their minimum illumination specifications. Without this detail, there is no way of knowing if blur-free images can be captured in low light conditions, without trying.

The animated image to the right illustrates the impact of shutter speed in low light conditions. The test subject was walking during each of the three frames taken at 1/10, 1/30 and 1/60 as indicated by the “exp” variable at the top of the image. The masked subject is holding a North American license plate with the last 4 letters [“HAWK”] exposed. Anything slower than a 1/60 shutter speed results in blurry images given the light level, reported as 0.7 lux by this particular Mobotix security camera.

Mobotix cameras have configurable minimum and maximum exposure times allowing for maximum flexibility. Their manual recommends a minimum exposure time of 1/60 for moving objects and 1 second for non-moving objects. Available shutter speeds for both minimum and maximum limits are shown on the left.

Shutter speed is less of a concern when monitoring inanimate or slow moving objects. For example: snow accumulations on roofs, water levels, agriculture or weather.