Description
A very popular lens for portraits. Nice build quality, all metal, long focus throw.
It's a Sonnar design derivative, the name Sonnar could not be used because it was registered for the western CZ company. So Jena decided to use "S" in the lens description. it's a fully multicoated lens (MC) in M42 screw mount. Older models weren't always multicoated.

Specifications
135mm F3.5 - F22 MC
3 elements in 4 groups
49mm filter size
6 blade aperture
90cm closest focusing
built-in telescoping lens hood

Measurements
89mm length, 430grams weight

Conclusions
Pros
Very nice build, smooth focussing
Sharp, even wide-open
Small and light, feels very nice on my E400
Long focus throw, makes focussing easy and accurate, even without a real split-prism focus screen. focus really "snaps" into focus.
Very nice bokeh.

Cons
135mm is 270mm on 43rds, so this makes the lens a bit long for general use.
Much sought after lens, so prices are relatively high on ebay (at least for good quality lens)

images:
The lens up close:


Lens on E400 (sorry, crappy mobile phone pic):


DOF test:


Portrait:


Leaf:


Colors:


Portrait:


It's been raining cats&dogs here, so the above shots were taken at high ISO (1600), not the best for good quality images. I'll post a follow up with better images (also full sized) once I get an opportunity to do some real shots.

Conclusion rant: very VERY nice lens, and it made me realize how much I missed high quality manual focus lenses. I'll be extending my collection of M42 lenses quite a bit, and will be buying the new Voigtlaender 58mm F1.4 NOKTON in pentax mount once available. If Olympus can't deliver, I'll go along this route.