I thought I'd compare a SMC Takumar 105mm f/2.8, a Soligor T4 mount 105/2.8, and for fun, a SMC Takumar 50/1.4 with a generic 2x tele converter.
Much to my surprise the Soligor walked away with the prize, at least among my samples of the lenses. Production and life time experience will make every lens somewhat different. The Tak 105 I'd bought from Eric Henderson, so it should be in good condition though.
The 50 + converter pics are invariably warmer than with the other two lenses - this probably the effect of remaining yellowing in the 50/1.4. The combo got reasonably good results closed down, and at the wider openings gave a nice vintage glow look that can be useful.
The shots are all Av mode, +2 EV, AWB, K100D. Oh, and I focused, with the confirmation light lit, on the back wall, so the rail and chair are in front of the focus plane. Not ideal, but more interesting than showing the wall. In retrospect, I'd put the chair or something in the center to focus on. However, the results are similar when I did a different series of comparisons on a central object surrounded by distant objects.
Soligor 105 at f/8
Takumar 105 at f/11
Tak 50 + 2x converter at f/4
Order in the crops: Soligor, Tak105, Tak50+2x
100% crops at f/2.8
100% crops at f/4
100% crops at f/11
JPEG file sizes:
Soligor 105:
f2.8 = 2.14mb, f4 = 2.33mb, f5.6 = 2.58mb, f8 = 2.60mb, f11 = 2.47mb
Tak 105:
f2.8 = 1.91mb, f4 = 2.15mb, f5.6 = 2.37mb, f8 = 2.3mb, f11 = 2.52 mb
Tak 50 +TC
f2.8 = 1.75mb, f4 = 1.88mb, f5.6 = 2.04mb, f8 = 2.18mb, f11 = 2.42mb
(click on images to get to the flickr pages, where full size versions of the 100% crops is available)