We reported the result of long term optical variability of the blazar 4C 29.45 ( QSO 1156+295 , Ton 599 ) , carried out optical photometric observations in Johnson V , Cousins RI passbands during April 1997 to March 2002 using the 1.56 meter telescope of the Shanghai Astronomical Observatory ( SHAO ) at Sheshan , China , compiled the post-1974 optical photometric data of the blazar by combining our new observations with the published optical data , and found maximum variations in different passbands : \Delta U = 4.41 mag , \Delta B = 5.55 mag , \Delta V = 4.53 mag , \Delta R = 5.80 mag , and \Delta I = 5.34 mag .
The average color indices are : U - B = - 0.54 \pm 0.18 mag , B - V = 0.56 \pm 0.21 mag , B - R = 0.93 \pm 0.18 mag , B - I = 1.51 \pm 0.24 mag , V - R = 0.44 \pm 0.15 mag and V - I = 1.03 \pm 0.23 mag .
The post-1974 data give us an excellent opportunity to search for the existence of possible periodicity in the light curve .
In search for periodicity in the R passband light curve , we performed Jurkevich test and power spectral ( Fourier ) analysis methods , and CLEANest algorithms to remove false signals .
We found possible periods of 3.55 and 1.58 years .
The possible mechanism for the periodic variability was discussed .