Of all the auto focus lenses I have ever bought, the Sigma E-mount 30mm f2.8 comes up on top of the value for the money category. I bought this lens along with the 19mm f2.8 when B&H had a dual lens deal for $199. Essentially, the cost of the lens is about $130 with taxes/shipping to Canada. It's indeed a great deal, especially when you factor in the exceptionally good optics that it possesses.
Build Quality
The lens has a metal mount, and high quality plastic lens barrel. It does not look or feel cheap. Compared to most plastic kit lenses, this one actually stands out as of very good build. For normal use, it will last a long time, I am sure. The electronics will probably die before you will see mechanical problems. It strikes a good balance between cost and quality of materials used.
Downtown Toronto - NEX-6 & Sigma 30mm f2.8. Click for larger.
Size
I think many people are disappointed that for this focal length and maximum aperture of f2.8, the lens is not pancake sized. It's just very slightly longer than the Sony E16-50mm kit lens, but almost twice that of the E16mm f2.8 pancake lens. Do I find this (relatively) larger size an issue? Not at all. The NEX-6 is not exactly a pocketable camera, even with a very thin pancake lens, it would be difficult to fit it in your pocket. I think the Sigma 30mm lens looks nice on the NEX-6. Would I like it smaller? Definitely, if image quality is not compromised.
Focus Speed
This is one aspect of the lens/camera combination that is disappointing. The NEX-6 is not exactly a speed demon when it comes to focusing speed. I can feel the difference between the Sony 50mm f1.8 OSS and this lens. I am not sure if it's due to the very cold (-10c) temperature, but this morning when I was shooting, even in very good light, sometimes it took a long time to achieve focus. It's not a deal breaker, but frustrating. One other thing. This lens does not support the new phase-detect auto focus feature of the NEX-6/5R. Not that it really matters much.
St. Lawrence Flea Market - NEX-6 & Sigma 30mm f2.8. Click for larger
Image Quality
A very cheap lens that does not produce quality pictures is not a good deal, regardless how little it costs. Fortunately, the Sigma 30mm f2.8 is one of the sharpest lenses I own. In fact, the lens out-resolves the 16 MP sensor by a such a large margin, that in many situations, moire is readily more apparent than other lenses. Already very sharp at f2.8, even around the edges. Stopping down improves sharpness but not by much. One has to wonder how Sigma could design and make a lens this good, and sells it for so little. If this lens is a bit wider, say 35mm equivalent, I would probably have it on the camera most of the time. It's one of the best bargains in auto focus lenses today.
What Don't I Like About This Lens?
Very little. I would like it to be a bit faster, both focus wise and in terms of maximum aperture, but then it wouldn't be selling at this ridiculously low price. The noise from the lens when not powered, is unnerving, but knowing that it was part of the design with a linear motor, I am sure it is not a problem. Also, this lens, unlike almost every lens Sigma ever sold, does not come with a hood. It's true that flare resistance is excellent on this lens, but I still would prefer to have a hood on it, mostly for protection of the front element.
Cement truck - NEX-6 & Sigma 30mm f2.8 @ f2.8.
Old & New - NEX-6 & Sigma 30mm f2.8.
