Spectral type estimation for the stellar companions with i − z > 0.21 corresponding to spectral types later than K5–K6. Red asterisks represent the synthetic values calculated by convolving the spectral library from Pickles (1998) with the transmission curves of the Sloan filters. Blue open circles represent the position of standard stars from Smith et al. (2002). Green filled squares are the measurements for our detected companions and their error bars (assuming no error in the software gain).