Infrared Optics & IFOV // Protocol IFOV-01
Thermal IFOV & Spot Size Calculator
Calculate Instantaneous Field of View (IFOV mrad), accurate 3x3 pixel Measurement Field of View (MFOV), and maximum target inspection distance for radiometric thermography.
10 meters (33 ft)
1m (Cabinet close-up)20m (Overhead line / Substation)100m (Tower inspection)
25 mm
Examples: 10mm breaker lug, 25mm bolted connection, 75mm insulator cap
Optical Spot Resolution Output
Fully Resolved
Target fills ≥ 3x3 sensor pixels (MFOV). Radiometric temperature calculation is mathematically valid.
Detector IFOV
0.33 mrad
0.019° single pixel
True MFOV Spot
10.0 mm
3x3 pixel spot size
Single Pixel Detectability Spot:3.3 mm
Max Safe Distance for 25mm Target:25.0 meters
Total Field of View (FOV):19.4° H × 14.6° V
Radiometric Physics Standards
The Physics of IFOV, MFOV, and Slit Response Function
1. Instantaneous Field of View (IFOV)
IFOV defines the spatial angle subtended by a single detector pixel through the optical lens:
IFOV (mrad) = Detector Pitch (µm) / Focal Length (mm)
A 17 µm detector with a 25 mm lens yields an IFOV of 0.68 mrad. At 10 meters distance, one pixel covers a physical square measuring 6.8 mm on each side.
2. The 3x3 Pixel Rule (Slit Response Function)
Detecting an infrared anomaly is fundamentally different from measuring its temperature:
- Optical Blur: Due to diffraction and optical dispersion, radiant energy from a sub-pixel hot spot bleeds across neighboring pixels.
- Radiometric Standard: To achieve 95%+ temperature accuracy without background dilution, the target must cover at least 3x3 pixels (the Measurement Field of View, MFOV = 3 · IFOV · Distance).