Optical analysis device for the determination of fine dust with - three light sources (L1, L2, L3) for emitting three emitted light beams (S1, S2, S3) with different wavelengths, - a device for combining the three emitted light beams (S1, S2, S3) on a common optical path , - a measuring volume into which gas laden with fine dust can be introduced and in which the emitted light (S1, S2, S3) strikes the gas to be measured and at which fine dust is scattered, and in the measuring volume a centre is defined from which scattering angles (α) are defined, the optical axis defining the scattering angle 0° in the forward scattering direction, - a light absorbing device at 0° which detects unscattered light, - a first detector disposed between 0° and 6° and immediately adjacent the light absorbing device and detecting scattered light in the forward direction, - a second detector arranged at a second scattering angle at 28°, - a third detector arranged at a third scattering angle at 61°, - a fourth detector arranged at a fourth scattering angle at 96°, - a fifth detector arranged at a fifth scattering angle at 128°, - a sixth detector arranged at a sixth scattering angle at 155° so that the detectors detect scattered light at the respective angle, - wherein each detector has an optical system (40-1, 42-1, 44-1, 46-1, 48-1, 50-1) which detects the light from a scattering angle tolerance range of +/- 1° and focuses it onto the respective detector, - a control and evaluation unit which drives the light sources (L1, L2, L3) so that the scattered light is detected wavelength-selectively by the detectors , - a memory for storing the detected scattered light intensities, - and the control and evaluation unit is designed such that the size distribution of the fine dust and fine dust mass fractions can be determined from the scattered light intensities. - three light sources (L1, L2, L3) for emitting three emitted light beams (S1, S2, S3) with different wavelengths, - a device for combining the three emitted light beams (S1, S2, S3) on a common optical path , - a measuring volume into which gas laden with fine dust can be introduced and in which the emitted light (S1, S2, S3) strikes the gas to be measured and at which fine dust is scattered, and in the measuring volume a centre is defined from which scattering angles (α) are defined, the optical axis defining the scattering angle 0° in the forward scattering direction, - a light absorbing device at 0° which detects unscattered light, - a first detector disposed between 0° and 6° and immediately adjacent the light absorbing device and detecting scattered light in the forward direction, - a second detector arranged at a second scattering angle at 28°, - a third detector arranged at a third scattering angle at 61°, - a fourth detector arranged at a fourth scattering angle at 96°, - a fifth detector arranged at a fifth scattering angle at 128°, - a sixth detector arranged at a sixth scattering angle at 155° so that the detectors detect scattered light at the respective angle, - wherein each detector has an optical system (40-1, 42-1, 44-1, 46-1, 48-1, 50-1) which detects the light from a scattering angle tolerance range of +/- 1° and focuses it onto the respective detector, - a control and evaluation unit which drives the light sources (L1, L2, L3) so that the scattered light is detected wavelength-selectively by the detectors , - a memory for storing the detected scattered light intensities, - and the control and evaluation unit is designed such that the size distribution of the fine dust and fine dust mass fractions can be determined from the scattered light intensities. <EOS>