Device for detecting properties of leaf-shaped article

The apparatus has an imaging device which converts light emitted by an illuminating device into a substantially parallel light pencil which illuminates a line in a line plane parallel to the sheet material and falls in a first illumination plane at a fixed angle of incidence, the first illumination plane forming with the line plane a first illumination angle and intersecting the line plane along the line. Light reflected along the line in a first detection plane at a fixed angle of reflection is imaged onto a detecting device, the detection plane forming with the sheet material a first detection angle and intersecting the line plane along the line. The angle of incidence is selected equal to the angle of reflection, and the first illumination angle equal to the first detection angle. For derivation of the magnetic properties of the sheet material components, the illuminating device preferably emits polarized light, and light specularly reflected along the line is analyzed before the detecting device by means of a polarizer.