λ=bsinθ=bsinϕ2
b=λsinϕ2
ϕ=300, b=550nmsin3002=2.125μm
ϕ=450, b=550nmsin4502=1.437μm
ϕ=900, b=550nmsin9002=0.778μm
ϕ=1800, b=550nmsin18002=0.55μm