Redshift constraints for RGB 0136+391 and PKS 0735+178 from deep optical imagingK. Nilsson, T. Pursimo, C. Villforth, E. Lindfors, L. O. Takalo and A. SillanpääA&A, 547 (2012) A1DOI: https://doi.org/10.1051/0004-6361/201219848