My understanding of why the bokeh varies across an image is that straight a circle aperture will appear as a circle on the image; however, the aperture will appear as an ellipse if viewed at an angle. This is why the bokeh at the top look stretched horizontally whereas the bokeh at the left & right look stretched vertically.
My understanding of why the bokeh varies across an image is that straight a circle aperture will appear as a circle on the image; however, the aperture will appear as an ellipse if viewed at an angle. This is why the bokeh at the top look stretched horizontally whereas the bokeh at the left & right look stretched vertically.