At f/3.5 (again I didn't see a possibility of setting it to f/3.3) the lens sharpness varies significantly, depending on distance from the center, but the worst problem is a low contrast. These are improved considerably at f/8 and f/11. At optimum apertures the sharpness is very good for small frame DSLRs. Edges of the frame are of poor quality. There is a 5.1% decrease 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 3.1% difference in extreme diameters, and this is a significant distortion. Interestingly, the largest ellipse distortion was on a 15mm chart (4.2%). This is unusual, especially when the direction of the smallest diameter shifts full 90%. The chromatic aberration noticeable.
Analysis at the 36 mm setting at various f stops is given here. It is the sharpest at f/8. 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 only very slightly lower than at f/8 or f/11, but very strange things happens to contrast - high at the center and sides and low in the mid-ranges. At the optimum aperture the lens performance is very good (resolution of "37" is the max. theoretical number in this test). There is a 2% decrease of the circle diameter at the edges 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 4% difference in extreme diameters, and this is a significant distortion. The chromatic aberration very low.
Analysis at the 300 mm at various f stops is given here. It has best performance 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.
What strikes the most is lack of contrast at full aperture between 6th and 15th mm. The contrast parallels the sharpness. At f/8 the performance is much better. The size of the circles as well as their roundness remain constant, so there are no distortions. The chromatic aberration is virtually non-existent. At this focal length and at f/8 and f/11 this lens performance is very good.
