Sigma 19mm f/2.8 EX DN lens review by Jordan Steel at Admiring Light: I should't like it, but I love it.

The lens was tested with an Olympus E-M5 camera, and Kudos to Jordan for not stripping the EXIF information from the images.

"The Sigma 19mm is a lens that frankly, I shouldn’t like. I’ve been using pretty much nothing but high end lenses for the past 6 years, and generally a budget lens like this wouldn’t even ping my radar. Then there’s that somewhat odd focal length, it’s relatively slow aperture and unremarkable size . But the fact of the matter is, I do like this lens. Sigma managed to make an affordable lens that is well built with a fast and silent autofocus motor. They then made it

surprisingly sharp with good color and contrast, packed in all the accessories you’d need and sold it for a pittance. Is it as good as the Panasonic 20mm f/1.7? No…it’s not. The Panasonic has a much larger aperture and is much smaller, all while being a little bit sharper on the edges (though the center is likely a wash). But that Panasonic costs over double what this little gem costs, and there’s that intangible: I love shooting with this lens. I know I shouldn’t…but I do. I have a blast with it on my camera. Sigma has made a great little lens, with high quality optics, and they have the decency to charge next to nothing for it. Well done!

Pros
Well built and generally compact (though much larger than competitors)
Very sharp in the center right from f/2.8
Extremely affordable
Very fast and accurate autofocus
Pleasing rendering with good color and contrast and neutral bokeh
Sigma includes an excellent lens hood and high end lens case with the lens despite its budget price
Cons
Image corners never get super sharp
Some longintudinal chromatic aberration and purple fringing can crop up from time to time
Lens is larger than competing lenses of similar focal length and aperture
The lens has an oddly long start-up period that lasts 3-4 seconds"

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