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Understanding Infrared Thermography Reading 3

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D ≡ αd<br />

D = spot size (approximate),<br />

α = field-or-view plane angle in radians,<br />

d = distance to the target.<br />

A 17.5 mrad (1 degree) field of view means a d∙D -1 ratio of 60 to1 and a 35<br />

mrad (2 degree) field of view means a d∙D -1 ratio of 30 to 1. (?)<br />

for D ≡ α∙d<br />

given that α = 17.5mrad, D=17.5mm if d=1000mm, thus<br />

d/D = 1000/17.5 = 57.296 ≈ 60<br />

This is to say the IFOV measurement ration = 1000 ∙ 1/α where α in mRad.<br />

Charlie Chong/ Fion Zhang

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