The presence of residual yarn on textile bobbins is recognized by a device capable of optically sensing and distinguishing yarn from a supporting bobbin or tube, which device is movable lengthwise along the bobbin or tube to perform a sensing operation. The sensing device includes a light source, a transmitter lens for focusing the light rays onto the surface of the bobbin, and a photooptic detector having a receiver lens for receiving the light rays reflected off the bobbin surface. The transmitter and receiver lenses have respective optical axes which, during sensing movement, are oriented to intersect one another at the bobbin surface, are oriented relative to the bobbin such that a line bisecting the axes deviates from a line intersecting the vertex of the axes perpendicular to the bobbin surface by at least ten degrees (10.degree.), and also lie in a common plane oriented at an angle of at least about ninety degrees (90.degree.) relative to the path of movement of the sensing device. Such orientation and arrangement of the transmitter and receiver lenses avoids direct reflection of transmitted light rays into the receiver lens, which minimizes any influence on the sensing operation by structural differences along the length of the bobbin.