Aperture and Depth of field

This is an illustration for my facebook  Photography group: Arunachal Photography and Film Lovers.

To understand Photography better and in order to have more control over one's photography it is important to get the basics of the camera function first. For that one need to understand, Aperture, Shutter Speed and ISO/ASA. 

Today, I will just touch the topic of Aperture and Depth of field resulting with the change of aperture.

What is Aperture?

Aperture is denoted by "f". An aperture is a hole or an opening through which light travels. Aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. The size of the stop is one factor that affects depth of field  (see below). Smaller stops (larger f numbers) produce a longer depth of field, allowing objects at a wide range of distances to all be in focus at the same time (like in the photo. Eg. f/16.
The aperture stop of a photographic lens can be adjusted to control the amount of light reaching the film or image sensor. In combination with variation of shutter speed, the aperture size will regulate the film's or image sensor's degree of exposure to light. Typically, a fast shutter will require a larger aperture to ensure sufficient light exposure, and a slow shutter will require a smaller aperture to avoid excessive exposure.

  

A device called a diaphragm (see the photo above) usually serves as the aperture stop, and controls the aperture. The diaphragm functions much like the iris of the eye – it controls the effective diameter of the lens opening. Reducing the aperture size increases the depth of field, which describes the extent to which subject matter lying closer than or farther from the actual plane of focus appears to be in focus. 

In general, the smaller the aperture (the larger the number), the greater the distance from the plane of focus the subject matter may be while still appearing in focus.

The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter. A lens typically has a set of marked "f-stops" that the f-number can be set to (see photo above). 

A lower f-number denotes a greater aperture opening which allows more light to reach the film or image sensor.

What is depth of field?

Depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. As you can see in the above photo, the depth of field is shallow in the widest aperture and it becomes considerably wider and sharper as the aperture decreases. 

As the depth of field becomes deeper and more in focus with the aperture diaphragm decreasing the light hitting the sensor or film pane also becomes lesser which results in slower shutter speed. With slow shutter speed, the camera becomes slower thus prone to shaky and blurry photos. Thus, it is important to use a tripod in such a situation or increase the ISO of the camera.

*Source Wikipedia. Diagram/ drawing of the aperture opening on the first photo taken from web.