B-band surface brightness of the stellar disk of M 33 plotted against deprojected radius. The background subtracted Sloan g-band was used to obtain the average value of circular apertures in the outer parts of M 33 disk where previously foreground stars and H ii regions were masked. The fit (solid line) was achieved using the isophotes in the radial range marked by the gray-shaded area. We obtain a final scalelength of 2513 ± 80 pc. The horizontal and vertical dashed gray lines indicate the 25 mag / arcsecond² isophote. The error bars are smaller than the data points.