The Olympus OM 28mm f3.5 is an inexpensive lens. My test lens has cleaning marks on the front element. Despite the coating flaw the lens is sharp. It handles well on mirrorless bodies and it east to focus, like all other Zuiko's I've tested. At f3.5 it is sharp enough to use w/out hesitation. It is very sharp with excellent contrast at f5.6. Flare causes a shift in color and a loss of contrast but it is natural to the eye. Color rendition is accurate with natural saturation. Shadow detail is quite good. Fringing can be seen at f3.5 in high contrast lighting when viewed at 100% crop. It is easily corrected. Vignetting isn't noticeable on the sub frame Eos M3. Distortion is also not noticeable. It is slow at f3.5, but it makes a good standard lens replacement for sub frame digitals. One surprising negative is bokeh fringing as It is noticeable passed f5.6.