How does the bokeh of the Sigma 50mm f/1.4 ART change when stopped down

1. Aperture design: The Sigma 50mm f/1.4 ART has a 9-blade rounded diaphragm, which generally helps maintain smoother bokeh even when stopped down compared to lenses with fewer aperture blades.

2. Wide open performance: At f/1.4, the lens is known for producing smooth and creamy bokeh. The bokeh quality is often praised as one of the strengths of this lens.

3. Stopping down effects:
- When stopping down, the depth of field increases, which typically reduces the amount of background blur.
- The bokeh circles (out-of-focus highlights) will become smaller as the aperture is stopped down.
- The shape of the bokeh may become more defined, potentially showing a slight nonagon shape due to the 9-blade aperture, especially in specular highlights.

4. Sharpness vs bokeh: While stopping down generally improves corner sharpness, it may come at the expense of some bokeh smoothness. The lens is noted to have sharp corners by f/2, suggesting that bokeh characteristics may start to change noticeably around this aperture.

5. Overall quality: Given the high-end nature of the Sigma ART series, it's likely that the bokeh remains relatively pleasing even when stopped down, though it will inevitably lose some of the extreme smoothness seen at f/1.4.

It's important to note that without specific test results for this lens at various apertures, these are general expectations based on typical lens behavior and the known characteristics of the Sigma 50mm f/1.4 ART. The actual bokeh performance when stopped down may vary depending on the specific shooting conditions and subject distance.