BVR photometry of comparison stars in selected blazar fields - I. Photometric sequences for 10 BL Lacertae objectsM. Villata, C. M. Raiteri, L. Lanteri, G. Sobrito and M. CavalloneAstron. Astrophys. Suppl. Ser., 130 2 (1998) 305-310DOI: https://doi.org/10.1051/aas:1998415