Abstract: The sheets (1,2) which are to be butt welded are positioned with their edges in contact with one another. To reduce the gap (3) to a width acceptable for laser welding, at least one sheet (2) is plastically deformed along the line of the joint so that material flows towards the gap, reducing the width of the gap. In this way, sheets cut to size with much less precision can be welded together.

Abstract: Photographs for detecting defects in the upper end face of the lip (43) of the mouth are taken by a camera (18) arranged on the axis of a bottle to be examined. An annular, coaxial light-conducting member (30), which is surrounded by a light source (28), is disposed between the lip (43) and the camera (18). It has a central viewing opening (40) with the shape of a double truncated cone (40a,40b). The generated surface of the truncated cone (40a) adjacent to the lip forms a light exit surface (46a) to illuminate the lip (43). The angle of slope of the truncated cone (40a) is selected so that an annular truncated cone of light (52) falls on the upper face of the lip (43) and has an angle of incidence of about 45.degree. in the middle thereof. This results in a dark-ground illumination of the lip (43). Should a defect be present in the region of the upper end face of the lip (43), this becomes visible as light on a dark background.