Summary: It's not as sharp as I expected. I'm spoiled I guess. All of my lenses are ZEISS or Minolta/Sony G series. I have two lenses that are not ZEISS or G series. The Sony 16mm distorts the way I want. This is my least favorite lens due to quality, sharpness and vignette. Does well outside in bright sunlight. Not so well in low light. I prefer my 16-35 ZEISS. But I will keep this lens so I can say I have every lens in every focal length.
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: Went I buy a prime lens (and I like them very much and have dozens of it), you expect to exchange the flexibility of a zoom for the sharpness and lack on aberrations of this type of lens. This is not the case of this lens. I have tried everything to tell myself that I was using it improperly and that it could not be that bad, but it is. Unfortunately, it is not only less sharp than all of my other primes (some of which cost 1/3 of its price).
Summary: This lens is identically the same as the which is a great lens. They are useable at f2.8, sharper at f4, and being wonderful at f5.6-f11. For sharper image with this lens, you may use the "front focus trick" If you have full frame A-mount camera, this lens is a must lens. Light fall-off is noticeable wide open, but is nearly gone at F/4. Coma is bad at F/2.8, but looks better at F/4.
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: I recently bought the Sony SAL-20F28 wide angle lens for my Sony A55 camera. I had Amazon ship the lens directly to my hotel room, as I was on holidays. As soon as I took it out of the box, I realized I was going to be quite satisfied. The construction, look and feel are superior. Then went outside with the lens and proceeded to snap off a few test shots. When reviewing them in my hotel room on my computer, I was very amazed at the clarity and crispness of the images.
Summary: I use this lens on an Alpha 850, and it's ideal for interior and exterior architecture as well as landscape. I should have purchased this lens rather than Sony's 16mm fisheye. The 16mm is fun, but the distortion only fits certain scenes and warp correction in Photoshop has its limits. The 20mm focuses very fast and is sharp at f5.6 and above. I mainly use a 24-70mm Zeiss, but the extra 4mm is really worth changing lenses when you can't back up far enough.