Left,Takumar S-M-C 135mm 3.5 @ 5.6. Center, Mamiya-Sekor CS 135mm 1:2.8 @2.8. Right, Takumar S-M-C 135mm 3.5 @ 3.5.

Those are crops downsized to 67% of their original size so that the whole fits on a wide screen. The main features are visible on the downsized montage.

On both the left and the middle shot the eye of the subject appears to be in focus. The focus of the right shot falls in front of the eye on the skin around the nose.

The MS at 2.8 looks almost as detailed and contrasty as the Takumar at 5.6.

Wide open the skin looks more contrasty on the MS shot than on the Takumar, but that may be the result of a slight adjustment in lighting between those shots. To compare the resolution, one has to look at picture "Montage 2" in this gallery where the focus is close to the eye for both lenses. Judging from the details around the eye both lenses show pretty much the same resolution.

A quick exposure check shows that the MS at 2.8 is 2 stops faster than the Tak at 5.6 as it should be.

Shooting in a bright flashlight, the Tak shows a strong ghost that gets dimmer as the aperture is stopped down. The MS shows no ghost with the same setup.