Summary: Here's the bottom line. If you're a professional photographer and make all your income from wide-angle lens photography, buy something else. Yes, there are some flaws in this ultra-wide lens, but only things that would be visible by someone taking Nat Geo pics or things for large-format printing. I have this lens attached to the 16mm wide-angle lens and the combo of the two is awesome. Great for landscape photography to get "the whole scene" into the shot.
Summary: I had this lens in mind when I purchased the 16mm pancake, but it took me almost a year to get this conversion lens. Now it almost never comes off the 16mm pancake. The 16mm is a little soft at the corners, but with the conversion lens, corners of the images appears sharper than the 16mm lens on its own. I've been using it mostly for indoors shots and walk around on the streets.
Summary: Recently, I made a trip to The Phila Art Museum, and took this add on lens with me. It fits over the Sony 16/2.8 lens only, and by buying it through Amazon, I got the best price on the market! I had other lenses with me, but used the wide angle set up most of the time. If I had to get a ceiling shot, I still had digital zoom, and the 24.2 MP camer still made a crisp shot. By the way that camera is a Nex 7, which I also purchased from Amazon.
Summary: This lens do what I expect it to do. It's quite a heft for such a small lens. I guess it's the optics accumulation inside. Is it sharp? I don't really have another similar lens to compare it with so I assume it's sharp enough for my need.
Summary: I needed a way to make the shot as wide as possible...this does the trick. If you want the 35mm equivalent of an 18mm, this is the least expensive way. It's not overly sharp but it works great for real estate.
Summary: I am extremely pleased with my just-acquired Sony ultra-wide angle converter for the 16mm lens on my NEX5n. It clearly exceeds my expectation that this attachment would provide a fully satisfactory ultra-wide angle. Actually, it does much more; first it easily clips onto the front end of the 16mm lens with a sturdy bayonet mount and a lock release. When attached it looks and feels like a single unit rather than an awkward appendage.
Summary: I bought this to test wide angle shots with the "only" recommended SONY lens that it will attach to ( make sure to research! ) and it works great. This would be great for tight shots in city places, interior of buildings, subway scenes, plant maintenance or getting shots in tight spots where you need to show the surroundings, etc. I've been completely satisfied with the quality of the resulting shots and the little amount of distortion caused. I would buy again.
Summary: This lens attached to my Sony Wide Angle has become my standard kit. The only problem is that the front element is so big there's no way to attach a filter. Still it doesn't seem to degrade sharpness or exposure at all.