The aperture series is for pixel peepers. Sample images are default in-camera JPEGs and are available at full resolution to show lens performance from center to corner. All images were shot on a tripod using electronic first curtain shutter and a remote release. In some cases, to emphasize a specific lens aberration, 100% crops are made available. Feel free to download the images for personal use, but please ask to repost them on other sites, and provide a link to this site when doing so. Thanks.
As the sample images demonstrate, the Batis f2.8 18mm is remarkably sharp over most of the frame right from wide open. Only the corners suffer some softness. Note that the lower right corners of the mountainside shots are soft at wider apertures because of limited depth of field. The lens was focused on the distant mountainside and the lower right corner is only about 4 feet away. The lens peaks about f5.6, where edge to edge sharpness is stunning and corner sharpness is quite good. By f16, the effects of diffraction are noticeable, but the images are still very sharp. I wouldn’t hesitate to stop down to f16, if the depth of field was called for. The full frame sharpness of the lens is superlative from f4 through f11, and it easily matches the high resolution sensor in the Sony A7RII.
Chromatic aberration is difficult to find at any aperture. What little there is can be easily corrected in post processing. Vignetting is also remarkably mild for such a wide lens. Starting at about 1.5 stops wide open and falling to a little under a stop by f5.6, vignetting is a non-issue for most compositions. Similarly, distortion is a non-issue for landscape work. Indeed the few interior and architectural images I made show the Batis to be a good performer in this regard as well. Because of the inherently large depth of field even wide open, I didn’t examine bokeh. The only opportunity I had to judge flare came on a clear night, where the moon in the frame corner shows some flare, which seemed to be well controlled. All around, the Batis 18mm put in a very good performance.
The night shots are included to show flare, coma, and astigmatism. Coma and astigmatism, in particular, are important for astrophotography, but have less impact on daytime landscapes. This is one of the few less than stellar areas in the lens’ performance. Wide open, the Batis showed pinpoint stars over much of the frame, but showed significant coma and some astigmatism toward the edges and corners. In the star images, the coma appears as stars being elongated radially toward the frame corners. The astigmatism, in this case, blurs perpendicular to the coma because the lens’ tangential resolution falls off toward the corners faster than sagittal resolution. The result is what is sometimes described as a duck, or a body with wings. See the 100% crops below to get a visual sense of what this means. While astigmatism improves somewhat by f4, coma seems to remain. Stopping down beyond f4 for astro work is generally avoided. Consequently, the Batis is a serviceable, but not stellar (no pun intended) performer for astrophotography.
Have a close look at the full resolution sample images and judge the lens merits for yourself.