How to Use Camera Aperture to Ensure Deep Focus
Deep focus is also referred to as Depth of field. Depth of field is the range of focus in an image, it is dependent on the camera aperture. Because focus happens gradually in the depth of field, some objects appear to be more out of focus than objects closer to the lens. This results in an image having depth and appearing layered. Using a basic portrait shot as an example, the subject is perfectly sharp and in focus, while objects a few feet behind them are slightly out of focus but still recognizable. But, an object 30 feet behind the subject is completely blurred. This helps create depth in a 2D medium.
How It Is Achieved
Depth of field has a great impact on the quality of an image. It is possible to achieve deep focus with optical tricks, but it is most commonly achieved by shooting an image using large amounts of light and a small aperture. It is the aperture of the lens that determines the depth of field. To achieve deep focus in your shot, you're going to need to make it very bright because you want to ideally be shooting at an f/5.6 or higher. F-stops are used to measure a camera's aperture and the higher the number, the more closed the aperture and less light coming through the lens.
Always Add Lights for Brightness
You always want to add more lights to a shot instead of opening the aperture. A closed aperture produces a higher quality image than an open one. It also produces an image with deep focus.