The interpretation of magnetic force microscopy (MFM) images requires knowledge of the magnetic structure within the tip. The etched polycrystalline iron, cobalt and nickel wires investigated all have their apex domain oriented along the tip axis. The image formation is found to be determined by an effective domain length L. For magnetization patterns of scales large compared to L, the point dipole approximation is applicable, provided that the tip apex can be treated as an isolated domain. While this is observed to be the case for cobalt tips, it does not apply to the most common tip materials, i.e. nickel and iron. The resolving power of a tip is given by its tip radius. At sufficiently small tip-sample distances, image forces induced by the strong tip field have been detected. MFM is used to investigate two Co-based longitudinal thin films. The roughness of the transition between head on oriented domains is compared. © 1991.