I purchased a 35mm lens some months ago, then again another 35mm only to find that 50mm and 35mm are so close and not worth having in MY opinion. So, I wanted to try a 28mm lens and thought of the Zeiss 28mm f/2.8 in silver but found a good deal on a new Ultron 28mm f/2 and decided to purchase it. It has been about 6 weeks now since I purchased it, I already shot a wedding and have done many comparisons to see how it handles color and sharpness. Its a decent lens with good quality, good optics and good resistance to flare or ghosting. Also, chromatic aberration is handled very well.
The wedding I shot was using it wide open f/2 and since the lens has focus shift over f/2.8 to f/11 I didn’t have any problems but if you plan on closing the aperture to f/4 and over, make sure you compensate for focus shift, it isn’t difficult, just practice and do samples to find its sweet spot. I purchased mine for $600 including shipping and a free B&W filter.
At f/4 and beyond, is almost as sharp as any other high end lens. So if you want the sharpest at f/2, obviously get some extra cash and buy the Summicron 28mm Asph, or just be happy with this one.
As a randome comparison, this lens is sharper at f/2.8 than the Nikon 17-35mm f/2.8 ED or any other Nikon-Canon in similar focal length at any aperture.