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1. Understanding focal length

Focal length refers to the distance from the optical center of a lens to the focal point where parallel light rays converge. In the context of surveillance cameras, it refers to the distance between the lens optics and the camera's CCD/CMOS sensor.

In a security camera, the focal length determines the image size, viewing range, and depth of field.

Field of View (FOV): The angle between the farthest edges of the lenses that encompass the area observable by the camera.

Depth of field: The area in front of the camera lens within which objects can be seen clearly.

1. The effect of different focal lengths

In modern security cameras, especially IP cameras, common focal lengths include 2.8mm, 3.6mm/4mm, 6mm, 8mm, 12mm and 16mm. Some cameras also feature variable focal lengths. Let's explore the differences between the various focal lengths.

Large focal length: Provides a narrow viewing range, suitable for distant observation.

Small focal length: Provides a wide viewing range and is suitable for close-range surveillance.

A larger focal length at the same distance will provide a narrower field of view but better detailed resolution.

For the same focal length, a larger distance provides a wider viewing range but reduces discrimination ability.

A large focal length is required to clearly capture the details of faces and human figures from a distance.

III. Choosing the right focal length for your surveillance camera

When choosing the focal length of your surveillance camera, consider the following factors:

Surveillance range: The focal length of a surveillance camera determines the size of the surveillance area and its effective visual range.

For small surveillance areas with a wide viewing angle (such as a living room or a small shop), choose a camera with a small focal length like 2.8mm or 4mm. These lenses have a viewing range of 75°-90° and effectively cover a space of 40²-80².

Choose a camera with a larger focal length for larger surveillance areas, such as spaces larger than 10m x 10m. However, a larger focal length will narrow the surveillance angle. To ensure comprehensive coverage, consider using a pan-tilt-zoom (PTZ) camera or multiple fixed cameras.

For remote, fixed surveillance ranges (such as monitoring a parking lot 30 meters away), choose a camera with a focal length of 12mm or greater.

If you prefer a simple approach, consider the following usage scenario:

For tight spaces like garages and warehouses, we recommend the 2.8mm focal length, which is suitable for surveillance up to 3 meters.

For indoor home environments and small shops, choose 4mm focal length, suitable for monitoring at 3-5 meters.

Ideal for monitoring areas such as residential gardens, balconies and entryways at distances of 5-10 meters