def METHOD_NAME(zs, vs=70, sep=500):
    ps1 = fourierHNA.GenShiftedPSF(zs + sep/2., vs)[::-1,:,:]#shift doesn't have parameters, so flip the image to reverse shift
    ps2 = fourierHNA.GenShiftedPSF(zs - sep/2., vs)
    return 0.5*ps1 + 0.5*ps2