Rikenon 135 mm f/ 2.8 Auto Lens

Moderately fast telephoto with really good bokeh at very low price point. Build quality is very good; focusing movement is very smooth and with a lot of play to allow for precise focus point. 8-blade aperture provides nearly round bokeh at f/4. 

Weaknesses:

Not multicoated. There is a fair bit of purple fringing and chromatic aberration. In some lighting conditions, there is a haze in the final images that takes away from the sharpness and color rendition. M42 mount will require an adapter for modern cameras. Nikon adater with glass element magnifies the fringing and aberration to a point where the lens is not useful. Works okay on Canon EF. 

Comments:

For a cheap lens, this thing delivers. It's not as sharp as a new Canon L lens, and the color rendition isn't all that accurate. But for the money, it's a nice option to have for a unique portraiture lens. Overall, a great value at around $35USD.