Seven-Year Multi-Color Optical Monitoring of BL Lacertae Object S5   0716+714
  We have monitored the BL Lac object S5 0716+714 in five intermediate optical wavebands from 2004 September to 2011 April. Here we present the data that include 8661 measurements which represents one of the largest databases obtained for an object at optical domain. A simple analysis of the data indicates that the object was active in most time, and intraday variability was frequently observed. In total, the object varied by 2.614 magnitudes in the $i$ band. Strong bluer-when-brighter chromatism was observed on long, intermediate, and short timescales. 
Yan Dai, Jianghua Wu, Zong-Hong Zhu, Xu Zhou, Jun Ma, Qirong Yuan,   Lingzhi Wang
astro-ph.HE astro-ph.CO