hi, im having trouble deriving an expression for converting between monochromatic flux expressed in wavelength and in frequency units. i think that the monochromatic flux of a star is found by F(Δf) = ΔE / ΔtΔfΔA F(Δλ) = ΔE / ΔtΔλΔA where E = energy, t = time, Δf = frequency bandwidth, A = area of photon collecting surface, and Δλ = wavelength bandwidth. i was shown how to do this question by my tutor but i cant remember how to do it, it involved differentiation or integration i think... so can you please help, its important that i find out how to do this quickly. thanks!! oh, and if you take the time to answer, could you please give me an explanation, as the answer itself doesn't really teach me anything, i'm more interested in how you found that answer.