Differences in Chromatic Aberration Correction,Thermal Stability Design,Priorities in Aberration Control,. Imaging Dependence Conditions,Anti-Interference Capability
What Are the Differences Between Infrared (IR) Lenses and Conventional Lenses?
The core differences between infrared lenses and conventional lenses lie in their response range to light, optical design objectives, and application scenarios. Below is a detailed comparison across four dimensions: technical principles, design differences, performance characteristics, and application scenarios.
Optical Design Objectives: Different Focuses on Aberration Correction
1. Differences in Chromatic Aberration Correction
Infrared Lenses:
Require correction of chromatic aberration within the infrared spectrum (e.g., dispersion in the long-wave infrared (LWIR) band of 8~14 μm). Aspherical lenses or diffractive optical elements (DOE) are commonly adopted. Combinations of germanium (Ge) and zinc sulfide (ZnS) can offset dispersion in the infrared band, achieving achromatism across a broad spectrum.
Conventional Lenses:
Focus on correcting chromatic aberration within the visible light range (e.g., focal length differences between red and blue light). This is achieved through low-dispersion glass (such as ED glass or fluorite glass) or floating lens groups.
2. Thermal Stability Design
Infrared Lenses:
The thermal expansion coefficient of materials must be strictly controlled (e.g., silicon has a thermal expansion coefficient of 2.6×10⁻⁶/°C) to avoid focal drift caused by temperature changes (e.g., military infrared lenses need to maintain image quality stability within the range of -40°C to 80°C).
Conventional Lenses:
Less sensitive to temperature, only requiring imaging stability under daily environments (e.g., -20°C to 60°C).
3. Priorities in Aberration Control
Infrared Lenses:
Prioritize eliminating thermal aberration and the impact of long-wave diffraction limits (e.g., the diffraction limit at 10 μm wavelength is 15 times that of visible light). Large relative apertures (e.g., F/1.0) or special optical path designs are necessary.
Conventional Lenses:
Focus on optimizing visible light aberrations such as spherical aberration, coma, and distortion, pursuing high resolution and edge sharpness (e.g., the MTF value of DSLR lenses is often >30 lp/mm).
Performance Characteristics: Imaging Logic and Environmental Adaptability
1. Imaging Dependence Conditions
Infrared Lenses:
Do not require visible light; rely on the object’s own thermal radiation (e.g., 9~10 μm infrared rays radiated by the human body) or active infrared light sources (e.g., 850nm/940nm infrared LEDs).
Imaging contrast stems from temperature differences between objects, not visible light reflection (e.g., clear capture of heat source contours at night).
Conventional Lenses:
Depend on ambient visible light illumination; imaging contrast is determined by the intensity of light reflected by objects (e.g., supplementary lighting or long exposure is required at night).
2. Environmental Penetration Capability
Infrared Lenses:
Long-wave infrared (8~14 μm) can penetrate smoke and light fog (e.g., forest fire monitoring), while mid-wave infrared (3~5 μm) is suitable for high-temperature targets (e.g., engine thermal imaging).
Less affected by strong scattering media such as rain and snow (penetration capability is superior to visible light).
Conventional Lenses:
Weak ability to penetrate haze and fog, easily affected by scattering from air particles (e.g., imaging becomes blurred when PM2.5 concentration > 300 μg/m³).
3. Anti-Interference Capability
Infrared Lenses:
Can avoid visible light interference (e.g., maintain imaging capabilities under strong light) but are prone to saturation from intense heat sources (e.g., flames, the sun).
Conventional Lenses:
Susceptible to overexposure or glare interference from strong light (e.g., backlighting, flash).
