Originally posted by AsTeTiX Just a quick realisation, I didn't specify that I use a Sony a6000 as the body.
I have the later K-mount SMC version of the 55mm 1.8 with an adapter for my Samsung NX30. The Sony cameras have a good focus peaking mechanism, so your setup should work much the same as mine. Both the 50mm and 55mm have nice, smooth focusing action. Handling-wise either lens are about as good as it gets when it comes to manual focus.
Although I never owned both at the same time and thus never compared the two directly, I did have a 50mm 1.7 which I liked very much. My impression of the M 50mm 1.7 is that it had a more contemporary rendering of scenes compared to the 55mm 1.8. The longer lens at maximum aperture has a different bokeh characteristic. It's not the extreme swirl some people go crazy for with the Russian Helios 44 58mm lenses, but it's got a certain
something that's hard to quantify. It's got... personality.
My M 50mm 1.7 had good sharpness shot wide open, but the 55mm 1.8 was also sharp with better micro contrast.
$35 for the 55mm 1.8 is a pretty good price, especially if you already have a M42 adapter for your Sony. I paid about double that for the K-mount version, which is still not bad considering the convenience of being able to also use the lens on my K-3 II. I think either lens would serve you well, it's just a matter of committing to using the darn things and enjoying photography!