An endoscope objective optical system includes a negative first lens group, a positive second lens group, a positive third lens group, and a negative fourth lens group, in this order from the object. Each spoke is disposed substantially circumferentially between two adjacent fixing apertures and the radially inner free edges of the radially outer circular part defining perforations with the free lateral edges of the spokes. In order to reduce the complexity of the crosstalk estimation calculations, the transmitter sends a measurement signal whose matrix includes a plurality of sub-matrices that include less than all of the signal slots and are modulated with QAM +1s or \u22121s.