The invention relates to an apparatus for inspecting the side walls of transparent bottles for the detection of dirt or foreign bodies therein. The inspection is effected by projecting a plurality of images of the side walls of a bottle, as viewed from at least two different directions in plan, on to at least one integrated circuit device comprising an array of photodiodes arranged in a plurality of rows in combination with means to interrogate each diode in turn, along each row in turn, to provide a video signal comprising a sequence of electrical signals corresponding to the light energy each diode has received. The two optical paths are so folded that over part of their lengths they are parallel and vertical, thus enabling both path lengths to be varied simultaneously by a common adjustment means, thereby to shorten or lengthen the object distance to obtain the appropriate magnification over a range of bottle sizes and make full use of the potential resolution of the photodiode array.