Bokeh (ˈbəʊkeɪ/)
the visual quality of the out-of-focus areas of a photographic image, especially as rendered by a particular lens.
The opening/aperture of your lens is what’s determining the shape of your bokeh. With a minor tweak, you can create amazing custom bokeh on your images.
Choose a prime lens with a wide aperture (F1.4 or F1.8).
Cut out a circle from a chart paper in the same diameter of your lens. On the centre of the circle, make a cutout on the shape you want, as shown in the below images. Tape the circle chart on your lens and make sure that no light is leaking through the edges.
Make sure that you are setting the stage with fairy lights or christmas lights for bokeh to show up.
