Bokeh is the effect made when lights are out of focus, this can be accidental or on purpose to make aesthetic background. By setting the camera to the largest aperture the camera will blur anything which is not being focused on.  We can also use manual focus to change which parts of the light are blurred, the more out of focus the larger the Bokeh light circles will be. The circle shapes which we see in Bokeh photos is simply the shape of the hole in the lens. This shape can be changed to a hexagon depending on the aperture, we can also make caps to go on our lenses which creat other shapes such as hearts. I used my 55-250mm lens to create a bokeh effect using fairy lights, I made a trail from the camera and up the wall to show what they look like at different focal lengths.

With the whole frame out of focus the light circles become larger and the whole image looks blurred.  When the image is slightly more in focus only the lights which are close to the lens make a bigger circle. Some of the wires in the mid ground are more in focus this is because the focus point was in the center of the frame.