The Hipparcos parallaxes allow us to revisit photometric calibrations in terms of Mv and to evaluate the effects of the overall metallicity across the HR-diagram. For evolved stars the spread in mass remains the major and irreducible source of errors in the photometric Mv. If the relative locations of open cluster main-sequences are fully explained by the ∆Mv versus ∆[M/H] relation, the residual scatter in the lower main sequence appears due to additional parameters such as rotation or gravitational settling of the heavy elements. These cannot readily be studied by a purely photometric approach.