With an aim to explore optical variability at diverse timescales in BL Lac source S5 0716+714 , it was observed for 46 nights during 2013 January 14 to 2015 June 01 when it underwent two major outbursts .
The observations were made using the 1.2-m Mount Abu InfraRed Observatory telescope mounted with a CCD camera .
On 29 nights , the source was monitored for more than two hours , resulting in 6256 data points in R-band , to check for the intra-night variability .
Observations in B , V and I bands with 159 , 214 , and 177 data points , respectively , along with daily averaged R-band data are used to address inter-night and long-term variability and the color behavior of S5 0716+71 .
The study suggests that the source shows significant intra-night variability with a duty cycle of more than 31 \% and night-to-night variations .
The average brightness magnitudes in B , V , R & I bands were found to be 14.42 ( 0.02 ) , 14.02 ( 0.01 ) , 13.22 ( 0.01 ) & 13.02 ( 0.03 ) , respectively , while S5 0716+714 was historically brightest with R = 11.68 mag on 2015 January 18 , indicating that source was in relatively high state during this period .
A mild bluer when brighter behavior , typical of BL Lacs , supports the shock-in-jet model .
We notice larger amplitudes of variation when the source was relatively brighter .
Based on the shortest time scale of variability and causality argument , upper bound on the size of the emission region is estimated to be 9.32 \times 10 ^ { 14 } cm and the mass of the black hole to be 5.6 \times 10 ^ { 8 } M _ { \odot } .