Sony's full frame mirrorless cameras wouldn't be much good without a sharp, compact lens to pair with them, and the 55mm f/1.8 Carl Zeiss is one such lens. The 55mm offers excellent image quality ratings, producing particularly sharp images with only minor softness towards the edges. The lens offers a nice wide f/1.8 aperture, ideal for blurring out the background, shooting in low light and using faster shutter speeds. Autofocus is also quick and quiet, making it a good lens for video as well. Besides just the solid image quality and performance, the lens is built well, with weather-sealing, and still weighs under 10 ounces.
With all those features in one, though, the lens is pretty pricey for a prime lens. While prime lenses offer more sharpness and wider apertures, the 55mm isn't very versatile. Besides just not offering zoom, the minimum focusing distance is pretty long. The lens also doesn't include image stabilization, though that's not a big necessity at this focal length. Like most lenses with apertures this wide, there is some vignetting. Overall, this lens is a solid performer and one of the top options for pairing with the Sony a7 line. Even users of Sony's APS-C mirrorless can use the lens, just at a longer 82mm focal length--the crop sensor will actually cut back the most troublesome parts of the image.