Selecting the Correct Lens for Video Surveillance

Introduction

In video surveillance, the lens is a critical component that can make or break image quality. Even with high-resolution cameras, the wrong lens can result in distortion, inadequate low-light performance, or insufficient detail for identification tasks. This guide focuses on practical considerations for surveillance applications—from wide-area monitoring at close range to long-range identification with PTZ cameras using lenses up to 120 mm.

In addition to focal length, the lens’s F-stop (aperture) is essential for controlling light intake and depth of field—both key factors in achieving optimal picture quality under varying conditions.

Key Lens Parameters for Surveillance

• Focal Length & Angle of View: The focal length determines the camera’s field of view. Wide-angle lenses (e.g., 2.8–4.0 mm) capture broad areas ideal for entrances and lobbies, while longer focal lengths (up to 120 mm) in PTZ cameras provide a narrow, long-range view.
• F-stop (Aperture): The F-stop defines how much light the lens can capture and affects depth of field. Lower F-stop values (e.g., f/1.8 or f/2.8) allow more light into the sensor—crucial for low-light conditions—whereas higher values (e.g., f/4.0, f/5.6) increase depth of field.
• Optical Quality: A high-quality lens minimizes distortion, aberrations, and color fringing. Even with a high-resolution sensor, poor optical quality can degrade image detail.
• Environmental Durability: Surveillance lenses must be built to withstand extreme temperatures, moisture, and potential vandalism.

Practical Surveillance Applications & Performance Data

• Entrance and Lobby Monitoring: Wide-angle lenses (2.8–4.0 mm) on 1080p or 3 MP cameras provide a broad field of view to monitor multiple entry points. Subjects within 15–20 feet can be reliably identified.
• Parking Lot Surveillance: Standard lenses (4.0–6.0 mm) on 3 MP to 5 MP cameras offer a balance between coverage and detail, ensuring clear facial and license plate capture for subjects 15–25 feet away.
• Long-Range Identification with PTZ Cameras: PTZ cameras equipped with telephoto lenses (12.0–120.0 mm) can zoom in on distant subjects. With appropriate F-stop settings (typically f/4.0–f/5.6), these systems maintain high image quality even for targets 30+ feet away.

Lens Performance Comparison for Surveillance

The table below compares various lens types used in surveillance. It shows their focal length ranges, F-stop ranges, angle of view, recommended camera resolutions, and typical applications.

Conclusion

In practical video surveillance applications, the correct lens selection is paramount. By understanding key parameters—focal length, F-stop, optical quality, and environmental durability—you can choose a lens that delivers the necessary balance of wide-