Angle of View
The angular extent of the scene a lens and sensor combination captures, usually quoted across the frame's diagonal.
Formula / rule
θ = 2 × arctan(d / 2f)
Measured in
degrees
In depth
Angle of view depends on both focal length and sensor size, which is why the same lens is 'wide' on one body and 'normal' on another. The relationship is not linear: going from 14 mm to 24 mm loses far more of the scene than going from 200 mm to 210 mm. Quoted figures are diagonal unless stated, so horizontal coverage is always narrower than the headline number.
Examples in practice
A 50 mm lens on full frame covers about 47° diagonally; the same lens on Micro Four Thirds covers about 24°.