In mechanized tunneling in hard rock using a TBM, the tunnel face cannot be characterized thoroughly even at periods with no advance. The tunnel face is obstructed by the TBM and hinders geological mapping and geometric rock mass characterization. As an improvement an autonomous imaging system is installed in inspection openings of the cutter head during maintenance shifts. By turning the cutter head it captures a circular part of the tunnel face with a digital video. The imaging system features its own light sources and orientation tracker. The video is processed off-site to a 3D image which then serves as basis for geological mapping or overbreak quantification. Detailed 3D images enable the measurement of penetration and they serve as permanent objective documentation of the actual rock mass conditions.