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Calculating Field of View

April 15, 2024

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Calculating Field of View

Have you ever wondered what the size of your imager’s field of view is at a given distance? If you know the visual field of view specifications for a thermal imager, it is possible to calculate the size of your imager’s viewing area for any given distance using a scientific calculator. The formula for this calculation is:

{(tangent 1/2 viewing angle) x distance} x 2

To apply the above formula, follow these steps:

1. Determine your imager’s Field of View (in degrees) from the manufacturer’s specs.

2. Divide the value from Step 1 by 2

3. Use scientific calculator to determine tangent of number obtained in Step 2

4. Multiply number in Step 3 by distance from imager lens to object.

5. Multiply number obtained in Step 4 by 2. This will be the width of the imager’s field of view at the specified distance.

Example: Calculate field of view for 16° lens at 25’.

(tan 8° x 25’) x 2 =

(0.140541 x 25’) x 2 =

(3.513525’) x 2 = ˜ 7.0’

If your imager specifies different Field of View values for horizontal and vertical, it will be necessary to calculate each value separately. Calculated values should be used for estimation purposes as actual values may vary slightly.

Imager operation is one of the many topics covered in all Infraspection Level I and Level II training courses. For more information on our Distance Learning Program or our open enrollment classes, visit us online at or call us at 609-239-4788.

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