Set it yourself.
Drag the slider. The eleven blades close the way they do in the lens.
Aperture
Wide open
At f/1.4 the most light comes in and the least is in focus. Backgrounds melt.
Stopped down
Each stop halves the light and deepens what is sharp, front to back.
Round, always
Eleven rounded blades keep the opening close to a circle, so points of light stay round.