This allows us to discard the tailing exponent and we have our answer: I ( θ θ ) = I 0 [ sinc ⁡ ⁡ ( π π a λ λ sin ⁡ ⁡ θ θ ) ] 2 ⋅ ⋅ [ sin ⁡ ⁡ ( N π π d λ λ sin ⁡ ⁡ θ θ ) sin ⁡ ⁡ ( π π d λ λ sin ⁡ ⁡ θ θ ) ] 2