nicolai , i want to add some comments but from photographer experience and not any n900 code

macro need special optics because is hard to achieve reasonable deep of field small aperture always help macro lenses have optimizations for close to lens light directions

portrait need also special optics large aperture to fade wrinkles and blur the background ( small DOF ), focal long enough to not distort the nose , good human skin color balance and modern times automatic red eye reductions

so ( my opinion ) the only optimization for n900 with fixed optics is aperture value : small on macro, large on portrait