One thing becomes apparent is the very poor flare resistance. With light coming from the side, flare quickly reduces contrast and makes the picture look washed out. Effective multi-coating is one advantage modern lenses have over the old lenses. Other than the flare issue, this lens performs quick nicely. Distortion is well controlled, and sharpness is quite good, but lacking the "bite" (micro contrast) of the best (expensive) lenses have. At f8, the edges on APS-C is quite respectable and shows good sharpness. No, it's not as sharp as the center, but not many low cost lenses are. It's definitely not a soft lens, especially with some post processing, the pictures exhibit good colour and sharpness.
A 24mm lens provides a comfortable 35mm field of view on the NEX cameras, and this Vivitar lens is a good choice for its low cost, but decent optical quality.
Vivitar 24mm & 28mm f2.8 with different mounts (M42/MD). Click for larger.
Vivitar 24mm & 28mm f2.8 without mounts. Click for larger.
Public Library - NEX-6 & Vivitar 24mm f2.8 TX mount. Click to enlarge.
Flare Test - NEX-6 & Vivitar 24mm f2.8 TX mount. Click to enlarge.
First Nation Art - NEX-6 & Vivitar 24mm f2.8 TX mount. Click to enlarge.
Church - NEX-6 & Vivitar 24mm f2.8 TX mount.