As Infrared Thermographers we are constantly aware of emissivity, focus, reflection, level, span, distance to target, IFOVmeasured and even our choice of pallet. While at the same time we are conscious of our surroundings, checking our PPE and staying safe. One area we are all aware of, but few give little if any conscious thought to is the Field of View available to our cameras.

Each camera has a Field of View (FOV) listed in its specifications. In some cases it is a single number (24°) in others there are two numbers listed (24° x 18°). These numbers represent the area visible to the camera detector from edge to edge, measured in degrees. In many situations this is not a major concern to us as imagers. We simply move closer or further away from our target to get the image we need.

Understanding the FOV of your camera is just as important as ensuring your batteries are properly charged.

• Can you get that water heater in a single image?
• How far away do you need to be to capture the side of that house?
• How much is viewable through that IR port?
• How high does the helicopter need to be for you to image the roof?

All of these are a direct result of your cameras FOV. So what do you do? Your pilot only has clearance up to a certain altitude.  That house is at the end of a dead-end street.  Where do you cut the hole to place an IR port in a transformer to see all the connections?  In certain situations you may need additional clearance or permission to move into restricted areas. If you are aware of your FOV limitations you can plan accordingly.

Another option is to actually measure your viewable area at different distances. Place your camera at a fixed point and measure out the distance to target. Now place an object in the center of your view (one with a Delta from ambient) and slowly move it to the side until it disappears. Move it back toward center until it is just visible through your camera and record that measurement. Multiply that number by two and that is your FOV at that distance. This will provide you real world numbers for you to work from. The following page is a report I provided to the staff placing IR viewing ports.

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IR Viewing Port Field of View

Camera = Flir P620

Rob Zimmerman

IR Level II

The chart below shows the measured viewable distance from centerline at given distances from the IR Viewing Port.

Example –A Standard Lens can view objects up to  19” on either side of centerline at 2.5 feet from the IR port (NOTE: This is to the outer edge of the object)

*** When determining IR port placement use measurements based on the Standard Lens with 0° offset whenever possible. This limits unwanted reflection and special equipment needs.

*** Any ports requiring the Wide Angle lens must be noted and the IR analyst advised of their locations.

**** All measurements are Line of Sight. IR cameras cannot see through Plexiglas, metal or any other obstruction. IR Viewing Ports are specially designed to be invisible to the IR cameras.

Thanks to Chris Rohde for his assistance.