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 represents the distance between the lens optics and the CCD/CMOS sensor of the camera.

For surveillance cameras, the focal length determines the image size, field of view, and depth of field.

Field of View (FOV): It is the angle formed by the two furthest edges of the lens that encompass the observable area from the camera.

Depth of Field: It refers to the range of distances in front of the camera lens where objects appear in sharp focus.

2. Effects of Different Focal Lengths In today's surveillance cameras, particularly IP cameras, the most 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 various focal lengths:

Larger Focal Length: Provides a narrower field of view, enabling distant observation.

Smaller Focal Length: Offers a wider field of view, suitable for close-range monitoring.

At the same distance, larger focal lengths provide a narrower field of view but enhanced detail resolution.

At the same focal length, greater distances offer a wider field of view but reduced identification capabilities.

To capture clear facial or human form details from a distance, a larger focal length is required.

III. Choosing the Right Focal Length for Surveillance Cameras Consider the following factors when selecting the focal length for your surveillance cameras:

Monitoring Range The focal length of a surveillance camera determines the size of the monitoring area and the effective visual range.

For smaller monitoring areas with a wide viewing angle, such as living rooms or small shops, consider cameras with smaller focal lengths like 2.8mm or 4mm. These lenses provide a field of view of 75°-90°, effectively covering spaces of 40²-80².

For larger monitoring areas, such as spaces exceeding 10m x 10m, choose cameras with larger focal lengths. However, keep in mind that a larger focal length will result in a smaller monitoring angle. To achieve comprehensive coverage, consider using pan-tilt-zoom (PTZ) cameras or multiple fixed cameras.

For fixed monitoring ranges but distant locations, such as monitoring a parking lot from 30 meters away, opt for cameras with focal lengths of 12mm or more.

Usage Scenarios Often, surveillance camera selection is driven by specific scene requirements. If you prefer a simplified approach without delving into intricate focal length parameters, consider the following usage scenarios:

For narrow spaces like garages or storage rooms, we recommend 2.8mm focal length, ideal for monitoring within 3 meters.

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

For areas like residential yards, balconies, or doorways, go for 6mm focal length, providing optimal monitoring within 5-10 meters.

Outdoor scenarios such as roads or alleys benefit from 8mm focal length, allowing for effective monitoring within 10-20 meters.

Certain long-distance fixed surveillance scenarios call for 12mm focal length, enabling monitoring from approximately 20-30 meters.

Additionally, some cameras offer variable focal lengths, allowing you to adjust the lens size based on the monitoring area range.

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