2007AJ....133.1599W

We first introduce a novel photometric system that consists of a Schmidt telescope, an objective prism, a CCD camera, and, in particular, a multipeak interference filter. The multipeak interference filter enables light in multiple passbands to pass through it simultaneously. The light in different passbands is differentially refracted by the objective prism and is focused on the CCD in separate regions, so we have multiple ``images'' for each object on the CCD frames. This system enables us to monitor blazars exactly simultaneously in multiple wave bands on a single telescope and to accurately trace the color change during the variation. We used this novel system to monitor the BL Lacertae object S5 0716+714 during 2006 January and February and achieved a very high temporal resolution. The object was very bright and very active during this period. Two strong flares were observed, with variation amplitudes of about 0.8 and 0.6 mag in the V' band, respectively. Strong bluer-when-brighter correlations were found for both internight and intranight variations. No apparent time lag was observed between the V'- and R'-band variations, and the observed bluer-when-brighter chromatism may be mainly attributed to the larger variation amplitude at shorter wavelength. In addition to the bluer-when-brighter trend, the object also showed a bluer color when it was more active. The observed variability and its color behaviors are consistent with the shock-in-jet model.