Why 90° Isn’t Always Optimal — Safe Distances & Scanning Angles Explained

Why 90° Isn’t Always Optimal — Safe Distances & Scanning Angles Explained

🔍 Thermal Imaging Techniques:

Why 90° Isn’t Always Optimal — Safe Distances & Scanning Angles Explained

Thermal imaging is a powerful diagnostic tool used across industries. From electrical maintenance and mechanical inspections to building diagnostics and predictive maintenance. But one of the most overlooked factors that can significantly affect accuracy is how you position your Thermal Imaging Camera.  Specifically, the working distance and scanning angle.

Let’s break down why simply pointing your camera head-on at 90° isn’t always the best approach, and what thermographers can do to capture more accurate, actionable thermal images.

🎯 The Myth of 90°: Why Straight On Isn’t Always Best

Many new thermographers are taught to aim for a 90-degree angle when capturing thermal images. The idea is to minimize reflections and maximize emissivity readings by capturing energy directly off the target surface.

While that’s a good rule of thumb in controlled conditions, real-world environments often throw curveballs:

  • Safety Hazards
    High-voltage panels, rotating machinery, hot pipes, or confined spaces often make it unsafe or impossible to achieve a perfect 90° angle. No image is worth compromising your safety. Always prioritize distance and protective barriers, even if it means sacrificing the ideal angle.
  • Reflective Surfaces
    Shiny metals like aluminum or stainless steel reflect ambient radiation. A straight-on angle may bounce external heat sources, like your body, sunlight, or nearby equipment, back into the camera, distorting the thermal image.
  • Obstructed Views
    Equipment enclosures, guard rails, ducts, or structural supports can block a clear line of sight. Scanning at a slight angle often gives better visibility without disassembling equipment.
  • Curved Surfaces
    Pipes, tanks, and motors rarely offer flat surfaces for direct imaging. A head-on view can produce uneven readings or reflections. Angling the camera helps capture more consistent thermal patterns.

📏 Working Distance: Don’t Get Too Close or Too Far

Thermal cameras have a spot size ratio (or distance-to-spot ratio, D:S) that determines how much area they’re measuring from a given distance. Entry-level cameras often have a lower D:S ratio, meaning:

  • Too far and the camera averages temperatures from too wide a spot. Potentially hiding small faults.
  • Too close and the image may not frame the entire object or be out of focus, especially on curved surfaces.

✅ Best Practice: Know your camera’s D:S ratio. For example, if it’s 300:1, standing 300 cm away will measure a 1 cm diameter spot accurately.

🚧 Scanning Around Barriers

Barriers and obstacles are common in real-world environments. Here’s how to work around them:

  • Use Adjustable Lenses or Tilt Screens: Some thermal imaging cameras allow angle adjustments for tight spaces.
  • Scan from Different Angles: Take multiple images from the left, right, and below if necessary. Cross-check results.
  • Keep Safety First: Never lean over energized equipment to get a better angle. 

💡 Pro Tips for Entry-Level Thermographers

  1. Scan at Multiple Angles: Compare thermal images from various viewpoints to verify anomalies.
  2. Avoid Reflections: Watch out for hot spots that mimic your own heat signature or sunlight glare.
  3. Use Context Images: Also record visual images with the thermal image to document perspective.
  4. Document Distance and Angle: Include this info in your reports.  Especially if repeat inspections are planned.

🔚 Conclusion

Getting the distance and angle right isn’t just a technical detail. It’s one of the most important parts of capturing clear, accurate thermal images. Knowing how and when to adjust your position can make a big difference in the quality of your diagnostics and the trust others place in your thermographic reports.

That’s why proper training is so important. Whether you’re just starting out at Level I or already working at Level II and beyond, understanding how distance and angle affect your results, and your safety, is essential. These are not once-off lessons. They require ongoing practice and learning.

For new thermographers, learning these skills early builds a strong foundation. For experienced professionals, it helps sharpen your edge and ensures you continue delivering reliable, professional results in every inspection.

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