Notice that the "blob" is octagonal? Both around the sun and the corona? That's your iris in the lens. This is one of those cases where you need to play with f-stop and shutter speed. Increase the shutter speed and lower the f-stop. Lowering the f-stop open the iris up and it becomes less visible. Also, the more you zoom in, the more noticeable it becomes.
Also be careful shooting directly into the sun without filters. You could damage the CCD (device that captures the light). At that time of the evening, you should be OK.