<P> A similar result holds for a small sensor imaging a subject at infinity: The angular resolution can be converted to a spatial resolution on the sensor by using f as the distance to the image sensor; this relates the spatial resolution of the image to the f - number, f / #: </P> <Dl> <Dd> Δ l ≈ 1.220 f λ D = 1.22 λ ⋅ (f / #) (\ displaystyle \ Delta \ ell \ approx 1.220 (\ frac (f \ lambda) (D)) = 1.22 \ lambda \ cdot (f / \ #)). </Dd> </Dl> <Dd> Δ l ≈ 1.220 f λ D = 1.22 λ ⋅ (f / #) (\ displaystyle \ Delta \ ell \ approx 1.220 (\ frac (f \ lambda) (D)) = 1.22 \ lambda \ cdot (f / \ #)). </Dd> <P> Since this is the radius of the Airy disk, the resolution is better estimated by the diameter, 2.44 λ ⋅ (f / #) (\ displaystyle 2.44 \ lambda \ cdot (f / \ #)) </P>

How the resolving power of an eye is estimated