I guess everybody heard about Takumar lenses quality and so many people use the common ones like 135mm Takumar lenses. They are sharp, quality built lenses. Imagine this quality in a faster, shorter focal length. This lens a perfect, portrait lens very well built, reasonable fast and sharp wide open.Quite rare lens show up two or three times per year on Ebay. In my opinion quality is good as than it's more expensive brother Takumar 85mm f1.8. I really enjoyed to work with this lens. Easy to handle , light weight, always a good performer.
This is an excellent lens that I have used off and on for portraits for about 30 years - starting when I took a portrait class in the Army! Also it is light and handy.
I use a 105/2.8 Super Takumar occasionally and it is an excellent portrait lens, comparable with the Canon 100/2.8 that I have but smaller and lighter. There was also an M42 SMC multicoated version too which might cope with flare better for a backlit portrait but the Super Takumar is fine with a lens hood on it.