I saw a previous topic for the Helios 44m-2, so I figured there was some love for the glorious plethora of m42 lenses available, and this particular one - the Asahi S-M-C f/1.4 50mm is my joint favourite lens (along with the Helios!).
Having a Canon f/1.8 50mm and being largely unimpressed, despite it's sharpness, I got this Asahi lens from ebay. Unfortunately it hits the mirror on my 5dmk3, so I have a clear bit of plastic acting as a shim, and the m42 adaptor is now not coming off the lens.
I much prefer this 50mm over the Canon - to me, the sharpness is comparable (if not better), and the out of focus areas are way, way better than the Canon. The Asahi lens cost me about £20 more than the Canon from ebay, which having no autofocus I guess is some sort of testament to the quality of the optics.
Below are a couple of images, the first, Birnbeck pier at Weston-super-Mare, was taken at f/11, ISO 50 with an infrared filter, which resulted in an 8 minute exposure.
The second image was when I took the lens out for a test run at the new Severn crossing; I figured I'd get something to show off the bokeh.
Hopefully it may convince someone to try something different!
Birnbeck pier, Weston-super-Mare:https://lh3.googleusercontent.com/-8QV81a2qRW4/UjdIc3S4zNI/AAAAAAAAMn8/xxRAsx7m6Sc/s800/birnbeck-pier.jpg