A system comprises a plurality of user devices and a conference call bridge connected to the plurality of end user devices via one or more networks. The incident beam of light is limited in spatial extent by imaging an aperture to form an illumination pupil, the centroid of illumination of the illumination pupil is aligned with the incident optical axis of the instrument. The insulating socket member has a plane contacting portion put in plane contact with a stem portion of the gas discharge tube, and a pin socket member into which at least one of stem pins, held in the stem portion is inserted in an electrically contacting state. A charge pump CP receives the charge pump current control signal CPCONT, and causes a current corresponding to the value to flow in or out. In a repetitive padding technique for an interlaced coded VOP, the even and odd lines of the VOP and surrounding block are grouped.