Voigtländer still produces a line of wonderful manual focus lenses today, and most of them are also available in M42 mount. they are quite expensive, and this lens costs around US$ 300.
The aperture is made up of 9 blades which should give an almost circular shape even when stopped down (importan for beautiful bookeh effect).
The lens is surprisingly small with a total length of only approx. 40 mm (1.6”).