Abstract: Imaging conditions for the aperture rays of an axial pencil, for example Abbe's sine condition, determine how an object volume will be imaged in the image space of an optical lens system. The invention provides an optical lens element having an imaging condition which analytically should lead to the largest possible volume in an image space wherein possible aberrations (spherical aberration and coma) remain below a certain prescribed level.

Abstract: A filter for treating a plurality of channels in a television signal cable distribution system comprises a plurality of paralel bandpass filters having a frequency which is individually controlled by frequency control voltages. A master filter provided with a filtering cell of a type identical to that used in a bandpass filter corresponds to each bandpass filter. For adjusting the central frequency of a master filter, a frequency is applied thereto by a frequency synthesizer and the cell is aligned with this frequency by acting on its frequency control voltage. This voltage is simultaneously applied to a bandpass filter for controlling the frequency, which is thus aligned with the frequency of the synthesizer simultaneously with that of the corresponding master filter. Each couple consisting of a bandpass filter and a corresponding master filter is realized by means of integration on the same semiconductor substrate (IC).

Abstract: A two-part housing, for holding a disc-shaped information carrier (15), for example a CD, has a bottom section (10), a cover section (11) connected to the bottom section via two corner hinges a (12, 13), and a clamping device (14, 14') for holding the information carrier (15). A simple fracture-proof hinge structure is provided in, that the cover section (11) comprises two hinge arms (18) whose free end portions (19) are bent through 180.degree. towards the cover section (11) and are resilient, the bottom section (10) has corner recesses (22) adapted to the hinge arms (18), and the free end portions (19) of the hinge arms (18), which end portions face one another, form in conjunction with rigid hinge walls (24) the corner hinges (12, 13).

Abstract: An image data recursive noise filter wherein relatively high spatial frequency components of the image data are either not filtered at all or are filtered to a lesser degree than relatively low spatial frequency components of the image data. This minimizes blurring of fine low-contrast detail and also avoids "freezing" of noise in undetailed moving areas of the image.

Abstract: A system for communicating digital data comprises a splitting device (38) for separating an input digital data word, which may be provided by a speech coding arrangement (34,36), into most significant bits and less significant bits. The most significant bit(s) of the digital data word are encoded (40) using a robust signalling alphabet and less significant bit(s) are encoded (42,44) using progressively less robust signalling alphabets. All of the symbols resulting from the encoding are combined (46) and transmitted (48). On reception (50) the received signal is split (52) and demodulated (54,56,58) to provide respective portions of a received data word to a combining means (60). Where the data word was originally provided by speech coding arrangement the received data word may be provided to a resynthesising arrangement (62,64). The signalling alphabets may comprise 2-level modulation, 3,4 and 8-level modulation and/or phase modulation of various degrees.