A microscope has a fiducial mask and fiducial lens generating a collimated mask image onto a beam splitter which directs the optical image to an objective lens where it is directed to an optical discontinuity formed by the change of index of refraction of the inner surface of a fluidic channel. Reflected optical energy is directed through the objective lens, the beam splitter, and a detector lens to a detector. A focused image forms when an inner surface of the fluidic channel is a focal distance from the objective lens, providing for imaging of fluorescent labels at the inner surface of the fluidic channel.