I bought an ultra wide-angle lens for my DSLR camera and the distortion in my photos is terrible; none of the lines of a building are straight. And there’s something else wrong with it; most of my outdoor photos are underexposed. Do you think this is unique to the lens that I bought or is it a common problem?
The complaint about distortion is common with any ultra wide-angle lens, Alex, and even with 18-55 mm zooms when they’re used at short focal lengths. However, the effect is caused by shooting technique and not a lens flaw. Granted such zooms usually do produce slight barrel distortion: a bowing outward of lines near the edges of the frame. However, that effect is minimal and not visible unless you take photos of something like a brick wall or a test pattern.
Many DSLR owners buy a wide-angle lens in order to cram as much into a single frame as possible. Often that requires tilting the camera upward: in order to include an entire building in the photo, for example. That tilting causes very obvious distortion of the perspective, because the bottom of the building is closer to the sensor than the top of the building. Such “linear distortion” is common but it can be prevented.
Hold the camera level, so the back—and hence, the digital sensor—is perfectly parallel to the subject. In order to include an entire tall subject in a photo, without the need to tilt the camera/lens, move much further back from the tall subject. Use this technique properly, preferably with a vertical composition, and a building should appear perfectly straight in the final image. Granted, a wide-angle photo may then include a lot of extraneous elements. To minimize that problem, use a longer focal length: zoom in more tightly to fill the frame with the subject.
And yes, images made with any ultra wide-angle lens can be underexposed: too dark. That’s because such photos often include a large light-toned area such as bright sky, snow, water or sand. Even the most effective light-metering system will not always produce a good exposure with such scenes. It’s usually necessary to use exposure compensation: a +2/3 or +1 setting will provide brighter images. Afterwards, be sure to return the compensation setting to zero; that will prevent making overexposed photos of scenes which do not include a large light-toned area.