As if I don't have enough 135mm lenses already: I have an excellent Pentax SMC-M 135mm f/3.5, a Carl Zeiss Jena 135mm f/3.5, a Pentax Auto-Takumar 135mm f/3.5, and a creepy plastic $2.00 Hanimex 135mm f/2.8 which is extremely bad. But the Takumar (Bayonet) is a K-mount, not an unhandy M42 mount, and is a stop faster than the SMC-M, so more light and shallower DOF.
But how does it stack up? here are the contenders:
I took some photos of our housing development's water tower, comparing it to the SMC-M. The color cast is different, as the Takumar (Bayonet) lenses did not have Pentax Super-Multi-Coating, but rather an ordinary multi-coating (they are not single-coated, a common rumor, but probably single-coated on the inner surfaces).
Anyway, the full frame:
|f/2.5||f/3.5 or f/4||f/8|
The Takumar (Bayonet) shows some obvious CA wide-open but shapes up admirably at f/4. I cannot really say that the SMC-M (which has a great reputation) wide-open is really that much better than the Bayonet at f/4 (one stop down). At f/8 of course they're pretty much identical.
A good buy, if I may say so myself. That f/2.5 could prove handy sometimes.