We present optical and IR surface photometry of M51 (NGC 5194) at B, V, R, I, J, K, and CO(2.3 μm). These data are used to establish whether K band (2.2 μm) images of spiral galaxies provide reliable maps of stellar surface mass density features such as massive spiral arms or bars. The main distorting agents in the mapping at shorter wavelengths are dust extinction and luminous young stars. From modeling the color changes across the main dust lanes in M51, we find the optical depths to be ∼0.5 in the K band. For these optical depths the K band flux is attenuated by only ≤10% even in the dust lanes