All those extreme wide angle lenses have lots of various problems, so bear in mind that this is one of the better ones on the market. At the most extreme wide angle, 12mm, the lens sharpness at the full aperture does not go down below 3000 LW/PH. Only at the very edge of the frame the image quality is questionable, being sharp only in the 10 to 4 o'clock axis, with a strong vignetting. For a standard digital SLRs the frame corner is around the 12th mm, so that the lens does not show those problems. Lack of contrast gives impression of softness.
At the optimum aperture, f/8, the lens performance is very good throughout the entire frame except the 4 corners (resolution of "37" is the max. theoretical number in this test). There is 4.3% increase of the circle diameter at the sides of the frame compared to the circle size at the center. This is about the same, but inverted ratio, compared with Canon prime EF 24mm f 1.4 lens. At the corners the circles are elongated, with a 9.7% difference in the extreme diameters of the ellipse. This distortion (enlargement and elongation) is clearly visible on arbitrary snap shots, and not only on test charts photos. Chromatic aberration is remarkably low.
Analysis at the 17 mm setting at various f stops is given here. It is the sharpest at f/11. Dependence of the image quality in various parts of the full 24x36mm frame is shown below, with the average resolution in hundreds of line widths per picture height (LW/PH) given below each chart.
At the full aperture the sharpness is considerably lower in the mid-range from the center (6 to 15th mm chart). At the optimum aperture, f/8, the lens performance is much better and the sharpness is relatively constant throughout the entire frame (resolution of "37" is the max. theoretical number in this test). The contrast is better than at the 12mm setting, making impression of even better better sharpness increase than it really is. There is only about 1.6% increase of the circle diameter at the sides of the frame compared to the circle size at the center (10 to 4 o'clock axis). At the sides the circles look elongated slightly, with a 5.3% difference in extreme diameters. The chromatic aberration is very low. It's a very good 17mm lens. Low vignetting.
Analysis at the 24 mm at various f stops is given here. It has relatively uniform sharpness between apertures f/8 and f/16. Dependence of the image quality in various parts of the full 24x36mm frame is shown below, with the average resolution in hundreds of line widths per picture height (LW/PH) given below each chart.
At 24mm the lens sharpness and contrast are the best, except at the very corners, showing variable directional resolution. The size of the circles remain pretty much constant trhoughout the frame. The circles roundness is also very good, distorted only by significant chromatic aberration (full frame cameras only). Low vignetting.
