In a real estate brokerage method through a video-conference, a purchaser and a broker meet with each other through an on-line VDC. The first inner hollow rail is accommodated within the outer hollow rail via the insulating device and is held in all directions transversely to the support rail in a positive-locking manner within the outer hollow rail by the insulating device. The selection can also process video inputs from the cameras either alone or in combination with the audio processing. Due to the rational design of the lenses according to the present invention, a minimal number of lens parameter increments can be identified to cover the range of common corneas.