In the process of improving the performance of concentrating solar collectors a variety of reflector materials are undergoing development. To allow comparable performance predictions, precise and replicable measuring methods are needed. In this paper we propose a measurement method and set-up (VLABS: very-low-angle beam spread) to determine the specular reflectance for variable angular acceptance. Our measurement set-up and method VLABS is advanced in measurement accuracy and speed, it gives as a result the specular reflectance for variable acceptance angles with an angular resolution of 0.03 mrad. We show exemplary results for a glass and an aluminum reflector and discuss the impact of acceptance angles up to 33 mrad on measured reflectance values at different wavelengths.