Back in 1967 this lens was sold as the budget option for the Singlex TLS. Mechanics are very well tuned. Focus dampening is perfectly balanced. Aperture clicks softly but firmly. The aperture ring is two sided. One side is manual and the other is auto. Aperture clicks are full stop with every other stop labeled. On the 6D. the image in the finder the prism is a bit dark, which made it difficult to focus. Luckily my M42 adapter has an AF confirm chip that actually works. I also found that I has to use center weighted metering to get an accurate reading. Is it any good? YES. It is sharp at the center from 2.8 with only a slight diffusion in bright edges. Corner sharpness is average at f2.8 but becomes good by f5.6. At f5.6 it is razor sharp in the center. Contrast is quite high and perhaps at the sacrifice of shadow detail. Fringing is practically non-existent. Vignetiing can be seen at f2.8 but reduces at smaller apertures. Barrel distortion is noticeable and a bit more pronounced than most standard primes. Black and white tonality is very good. The best characteristic of this lens is its IQ. Pics have a 3D feel which is reminiscent of EBC Fujinon's and Konica Hexanon's.