Abstract: An optical shift fluid flow velocity measurement mechanism is shown and described. A fluid flows over a bluff body to produce a vortex street. Downstream of the bluff body a light beam emission source directs a beam of light towards a lenslet including a light transmission gradient. Light transmitted through the lenslet is perceived by a photovoltaic cell which generates an electrical signal. Vortices in the vortex stream disrupt the light beam, affecting the amount of light transmitted through the lenslet and perceived by the photovoltaic cell, thereby changing the electrical signal. The frequency of the changes in the electrical signal can then be correlated to the velocity of the fluid flow.