Comparing the Sonnar types to the double Gauss types really isn't fair. The Sonnars evolved as a large-aperture lens in the early 1930s, when lens coatings were not available. They gave a very good performance with a minimum of internal surfaces -4- compared to the dG, which has a minimum of 6 internal surfaces. The dG type had somewhat better performance at maximum aperture, but the price paid was flare. The Gauss lenses really had to wait for coatings to do their job well.

Canon LTM lenses -