Bokeh
Simulator
AI generated demo image
No aperture opens in these shapes. They come from a card with a shape cut out of it, held in front of a fast lens: the cut-out becomes the narrowest opening the light passes through, so every out-of-focus highlight copies it. It costs two or three stops of light and only works with the lens wide open.
What shapes bokeh
Bokeh is the look of the out-of-focus parts of a picture. Every unfocused point of light is spread into a small image of the lens's opening, so the shape and texture of that opening are printed all over the background.
Circular bokeh
A wide-open lens, or one with many curved blades, has a round opening, so highlights blur into smooth discs. This is what most modern portrait lenses aim for.
Blade polygons
Stopping down closes the aperture blades. With few straight blades the opening becomes a pentagon or hexagon, and so does every highlight. Nine curved blades stay close to round.
Cat's eye
Toward the edges of the frame the lens barrel itself cuts off part of the opening, so discs become lemon or cat's-eye shapes. It fades as you stop down.
Swirly bokeh
Some vintage portrait lenses stretch discs around the centre of the frame, so the whole background seems to swirl around the subject.
Donut bokeh
Mirror (catadioptric) telephoto lenses have a mirror blocking the middle of the opening, which turns every highlight into a ring.
Soap bubbles and onion rings
Some lens designs concentrate light at the edge of each disc, giving a bright rim like a soap bubble. Lenses with aspherical elements can add faint concentric rings inside the disc.
Custom shapes
A cut-out shape taped over the front of a fast lens, like a heart or star, becomes the aperture, and every highlight takes that shape.
Size of the discs
Bigger apertures (smaller f-numbers), longer focal lengths, closer subjects and more distant backgrounds all make bokeh discs larger.