How to Choose an LWIR Athermal Lens (Long-Wave Infrared Lens)

Table of Contents:

1. Introduction to LWIR Athermal Lenses

• What is an LWIR lens?

• Why athermal design matters

2. Understanding the 8–14 μm Infrared Band

•  Wavelength range and imaging characteristics

3. Key Parameters for Lens Selection

   3.1 Focal Length
   3.2 F-number (F/#)
   3.3 Minimum Focus Distance
   3.4 Field of View (FOV)

4. Main Application Scenarios

    4.1 Thermal Imaging

   4.2 Security and Surveillance
   4.3 Environmental Monitoring

   4.4 Industrial Inspection & Non-Destructive Testing

5. Step-by-Step Lens Selection Checklist

6. Conclusion and Best Practices

Long-Wave Infrared (LWIR) athermal lenses are specialized optical components designed for the infrared spectral range, typically operating in the 8–14 μm wavelength band. They are widely used in thermal imaging, security monitoring, environmental sensing, and industrial inspection.

This guide explains the key parameters to consider when choosing an LWIR athermal lens and outlines the main application scenarios.

Key Parameters for Selecting an LWIR Athermal Lens

1. Focal Length

• Definition: The distance (in millimeters) from the lens to the focal point.

• Impact:

Short focal length → Wide field of view, captures more area but with less magnification.

Long focal length → Narrower field of view, higher magnification for distant objects.

• Example: A 19 mm LWIR lens offers a wide-angle view, while a 100 mm lens focuses on distant targets.

2. F-number (F/#)

• Definition: The ratio of the lens’s focal length to the effective aperture diameter (e.g., F/1.0, F/1.2).

• Impact:

Smaller F/# → Larger aperture, more infrared energy reaches the sensor, better low-light performance.

Larger F/# → Smaller aperture, deeper depth of field but less light.

• Tip: For thermal imaging in low-emission environments, choose a lower F/# (e.g., F/1.0).

3. Minimum Focus Distance

• Definition: The shortest distance at which the lens can focus on a target.

• Impact:

Shorter minimum focus distance → Better for close-up inspection or small object imaging.

• Example: For PCB thermal testing, a lens with a <0.5 m minimum focus distance is preferred.

4. Field of View (FOV)

• Definition: The angular range captured by the lens, expressed in degrees or radians.

• Impact:

Wide FOV → Better situational awareness, suitable for area surveillance.

Narrow FOV → Detailed observation of distant objects.

• Tip: Match FOV to the target size and working distance for optimal resolution.

Common Applications of LWIR Athermal Lenses

1. Thermal Imaging

• Detects infrared heat radiation from objects.

• Used for temperature mapping, identifying hot spots, and visualizing thermal patterns.

2. Security and Surveillance

• Provides clear images in total darkness.

• Ideal for border security, perimeter monitoring, and intruder detection.

3. Environmental Monitoring

• Detects abnormal temperatures in wildfire prevention, gas leak detection, and pollution monitoring.

4. Industrial Inspection & Non-Destructive Testing

• Identifies overheating in machinery, electrical faults, and hidden structural issues.

• Improves maintenance efficiency and prevents costly failures.

Checklist for Choosing the Right LWIR Athermal Lens

1. Define your application (security, industrial, environmental, research).

2. Determine required FOV based on target size and distance.

3. Select focal length to balance magnification and coverage.

4. Match F/# to lighting and sensitivity requirements.

5. Check minimum focus distance for close-range needs.

6. Consider environmental stability (athermal design ensures performance over temperature changes).

Conclusion

Choosing the right LWIR athermal lens is about balancing optical performance parameters with your specific application needs. By carefully considering focal length, F-number, minimum focus distance, and field of view, you can ensure your thermal imaging system delivers maximum accuracy and reliability.