Low-light performance of a surveillance camera is critical in both dark indoor environments and nighttime outdoor environments. There are four low-light features to consider when looking at IP surveillance solutions:
The amount of light that reaches a camera’s image sensor is determined by the lens in front of it. The lens is the optical path through which light travels and the lower the f-stop value, the more light reaches the sensor. The f-stop is used to measure the aperture or iris setting of the lens. The higher the f-stop, the smaller the iris (f16), and the lower the f-stop, the larger the iris (f1.2).
The trade-off with a large iris is the depth of field becomes shallow, especially on a telephoto lens. Depth of field is the range of distance where subjects are in focus. We’ve all seen great looking portrait photos where a close-up of a face fills the frame and the background is intentionally soft and out of focus. In the world of fashion, photography and art, this is quite often a desirable effect. In the world of surveillance, it’s the last thing you want. Luckily with wide angle lenses, the depth of field increases and usually everything in the scene is in focus. But even with a wide angle lens, the larger the iris setting (i.e. the lower the f-stop), the more shallow the depth of field becomes. So there is a trade-off to using a low light, large iris lens — a potential reduction in focus/depth of field.
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