Convert Hydrogen column to an extinction coefficients, using Predehl & Schmidt 1995?:
`A_V = frac{N_H}{1.8xx10^21}` cm-2

`E(B-V) = frac{A_V}{R_V}`, where `R_V=3.1` for the Milky Way

How to change flux density from wavelength to frequency:

`F_lambda d lambda = F_nu d nu`

`F_nu = F_lambda frac{d lambda}{d nu} = F_lambda frac{lambda^2}{c} = F_lambda frac{lambda^2}{2.998xx10^{18}}`, where lambda is in Å