Probing the dark matter issue in f(R)-gravity via gravitational lensing M. Lubini, C. Tortora, J. Näf, Ph. Jetzer and S. Capozziello Eur. Phys. J. C, 71 12 (2011) 1834 Published online: 22 December 2011 DOI: 10.1140/epjc/s10052-011-1834-8