Focal Length and Fixed Focus
Focal length refers to the distance between the optical center of the lens and the image sensor, typically measured in millimeters (mm). It determines the camera's field of view and magnification, making it a critical parameter that influences image perspective and spatial depth.
In body cameras, fixed-focus lenses are commonly adopted—these lenses have a preset, non-adjustable focal length and are ideal for quick deployment and easy operation in fast-paced field scenarios.
1. Key Features of Fixed-Focus Lenses
- No manual focusing required: The camera delivers clear images immediately upon power-on, simplifying operation during field use.
- High reliability: Without a motorized zoom mechanism, the lens is more resistant to shock and mechanical failure.
- Wide depth of field: With a properly selected focal length, fixed-focus lenses provide sharp images from near to far distances.
2. Focal Length vs. Field of View
A shorter focal length results in a wider field of view and broader image coverage.
A longer focal length provides a narrower field of view, magnifying subjects but reducing the visible range.
| Focal Length (mm) | Horizontal FOV (HFOV) | Description |
|---|---|---|
| 2.1 mm | 130°–140° | Ultra wide-angle, panoramic view |
| 2.8 mm | 110°–120° | Moderate wide-angle, mainstream |
| 3.6 mm | 90°–100° | Narrower view, sharper subjects |
Note: Actual field of view also depends on the sensor size. Values above assume a standard 1/2.8" sensor.
3. Focus Range
Though fixed-focus lenses cannot be manually adjusted, they are factory-calibrated to operate within an optimal focus range:
- Typical range: 0.5 meters to infinity (∞)
- Designed to clearly capture people and objects from standard chest-mounted height
- Optimal clarity distance: 1.5 to 3 meters — ideal for close interactions and evidence collection
Shelleyes Implementation
Shelleyes body cameras widely utilize fixed-focus lens structures with optical focal lengths ranging from 2.5 mm to 3.2 mm. This range achieves a strong balance between wide-angle coverage and image clarity, making it suitable for diverse law enforcement scenarios.
This design ensures rapid and reliable imaging even in sudden, no-preparation recording situations. It is a foundational element supporting the high reliability and operational readiness of Shelleyes body cameras.