Filming & Production
Aperture
Also called: f-stop, f-number, iris
A lower f-number means a wider opening. At f/1.8 far more light gets in and the background falls away behind the subject, while stopping down to f/8 holds more of the scene sharp. That trade is why the control exists.
Talking heads usually live around f/2.8 to f/4. Wide open on a fast lens looks lovely on a still photograph and punishes you on video, because a focus depth measured in centimetres means leaning towards the camera puts your own eyes soft. Most lenses also have a sweet spot a stop or two down from wide open.