- 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.
- 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
