An optical scanning device (1) for scanning an information layer (2) includes a radiation source (6) for supplying a radiation beam (14), a lens system (7) having an optical axis (OO'), and a detection system 8) including: (i) an astigmatism generating element (9) for generating a first amount of astigmatism (W.sub.1) represented by a vector (W.sub.o,1, .theta..sub.1), so as to transform the radiation beam to a first astigmatic radiation beam (29); (ii) an astigmatism correcting element (27) for generating a second amount of astigmatism (W.sub.2) represented by a vector (W.sub.o,2, .theta..sub.2), so as to transform the first astigmatic radiation beam to a second astigmatic radiation beam (30) having a third amount of astigmatism (W.sub.3) represented by a vector (W.sub.o,3, .theta..sub.3), and (iii) a detector (28) for transforming the second astigmatic radiation beam to an electrical signal. According to the invention, W.sub.3 is adapted to the detector and that W.sub.o,2 and .theta..sub.2 comply substantially with the following equation: (W.sub.o,1, 2.theta..sub.1)+(W.sub.o,2, 2.theta..sub.2)=(W.sub.o,3, 2.theta..sub.3).