Summary: I purchased this lens for my a99 body for the purpose of capturing indoor photography of subjects (head to toe). I found my 50mm f1.4 and a CZ 85mm f1.4 lenses are both great in low light, but I find myself really constrained when trying to distance myself from my subject (especially in a 10x10 sized room). With this 20mm, I can stand approx. 3-4 feet and be able to capture the full subject in frame. The issue is with the amount of light indoor shooting provides.
Summary: I bought this lens used for a trip to France; I anticipated being in very old buildings with low light and no flash permitted. All of that turned out to be true and the lens performed very well. Notre Dame, for instance was dark with a great amount of detailed stone work, art work etc. I switched my camera (Sony A 350) to Aperture Priority and managed to get good pictures in spite of the lack of light.
Summary: This is a light weight, compact lens. If you are looking for wide angle, fast lens this is the lens for you. Photos come very sharp in low light condition using F/2.8. It is easy to carry around, good to take landscape photos as well as architecture. Comparing with Sony 11-18mm f/4.5-5.6 Zoom Lens, vignetting at the edges and distortion is almost none. The bokeh is really nice on the background of your main subject.
Summary: This is a truly superb prime wide-angle lens, works flawlessly on a900 - full-frame wide lenses are hard to come by, but I would strongly suggest getting this. Super-sharp from f4 onwards, still delightful and fast at 2.8; great colours and depth.
Pros: Consistent Output, Lightweight, Quick Focus, Sharp Focus, Strong Construction
Summary: Underbart objektiv som ger rejält bra kontrast och färger redan vid 2.8 enl. mig. Har heller inte noterat någon kromatisk abression eller vad det kan tänkas heta på svenska. Det finns dock aningen "barrel distortion" dvs att bildet kurvar sig en del och det märks ännu tydligare om man har fullfortmatssensor. Med en aps-c kamera så vinjeterar den inget alls. inte ens om man har dubbla filter på den.