In reflective concentrating systems, mirrors play an essential role in directing and concentrating the energy from the sun to the modules. Shortcomings like misalignment, shading or bending of mirrors, due to their weight or wind, imply a higher probability of attenuated energy and non-uniform illumination on the receiver. The objective of this work is to design and test a method to assess the optical quality of solar concentrators, based on the absorber reflection method (ARM), which allows minimising the distance from the camera to the concentrator. The proposed procedure allows the characterization of the optical quality of reflectors when the concentrator is working at different inclinations tracking the sun’s movement. The validation measurements were performed in a two-axis Fresnel reflective solar concentrator. Results from the method developed were included in two numerical procedures, ray-tracing and the sum-of-squares. From these simulations the overall effects of the optical quality and the sunshape over the absorber were considered and compared with the measured experimental concentrated flux distribution profile.