Vivitar 28mm f2
This lens has a good reputation. It was made by Kiron and made well. My test lens has a Minolta MD mount. It handled well on the Eos M3 even though there was a little play in the adapter. Focusing was not an issue except for the normal difficulties with wide angles. The lens is f2-f16 with half stops. It's not too big or too heavy on a mirrorless body. The focus ring on my copy is a little stiff. That is not unusual as the grease solidifies over time.
This lens is what I would expect from Kiron. It is soft a f2 but tightens up to very sharp at f2.8 w/ excellent contrast. At f3.5 it is very, very sharp. At f5.6-f8 it is stellar, except for one issue.
Most of this lens' faults happen at f2. Fringing, clipping in highlights, low contrast and diffusion happen at f2. There is on fault that happens at all apertures. FLARE.
Flare is an issue. See pics below. Don't leave the house w/out a lens ood and don't shoot toward the sun. You will be pounished for your forgetfulness.
Distortion is welll controlled. This is a good standard lens on a sub frame body.
B/W looks very good from this lens. Color rendition, saturation and shadow detail are typical of Kiron glass. Colors are slightly subdued, a bit bluish and the high contrast of the lens steals detail from shadows. Kiron is very much like Nikon in many ways. That makes sense because Kiron was founded by ex-Nikon staff who weren't happy with the plastics in 80's Nikon lenses.
Overall, this is a very good lens. It does suffer from flare but most 28mm's do. At f2.8 is very sharp. It makes a good normal length lens for mirrorless bodies.
ISO 400 - f2 thru f8
flare, flare, flare
ISO 400 - f2.8 - 100% crop - 10 feet
ISO 400 - f2 - simple b/w conversion
ISO 400 - f3.5 - 100% crop - very sharp
ISO 400 - f2.8
ISO 400 - f2 and f2.8 - 100% crop
sharpness & contrast
ISO 400 - f2 and f4
contrast & bokeh