Endoscopic optical systems have a metal housing which is generally constructed in the form of a tube in its distal region and with a broadened portion in its proximal end region. A window is provided at at least the distal end of the housing through which the optical device of the optical system can look outwardly with an objective. In endoscopes with an optical eyepiece, a window which enables one to look in is also provided at the proximal end. The windows are usually constructed as plane parallel plates of e.g. glass which are connected to the housing in a sealed manner at their edges.
The connection of the window to the housing is effected in optical systems of the type referred to above by soldering in a marginal gap between the cylindrical outer edge surface of the window and a cylindrical internal surface on the housing, as is illustrated in relation to the example of the distal window in DE 37 40 417 A1. As explained therein, the edge of the window is metallized in constructions of the type referred to above in order to render soldering possible, which can only be effected between metal surfaces.
The known construction referred to above requires very careful soldering of the entire window edge. It has, however, transpired that this is disadvantageous since soldering over the entire area of the edge or side surface of the window produces stresses in the glass which can lead to breakage. This occurs particularly as a result of current requirements on endoscopic optical systems as regards sterilizability which can only be fulfilled by frequent autoclaving, that is to say hot steam sterilization. The rapid changes in temperature associated therewith promote stress cracks in the glass.
An endoscopic optical system with a soldered window, which is not of the type referred to above, is disclosed in DE 196 44 729 A1. The cylindrical window is secured in a metal tube by introducing adhesive into the gap between the window and the housing. Corner soldering is provided on the internal surface of the window on an appropriately metallized annular portion of the internal surface of the window. This construction is, however, difficult to manufacture as a result of the soldering process within the tube and results in a reduction in the usable area of the window.