Aperture Priority Mode
This is for camera owners whose cameras have never been off the Automatic setting, but have a series of off mysterious letters on the dial. “Automatic setting” includes “just point and shoot” and the so called “scene modes” that the camera maker labels with little icons for close-up (usually a flower), portrait (head), sports (running man), landscape (mountains) and the like. I have one camera with dozens of these scenes available, even down to settings for parties, snow and food!
Now, whether you set these by turning a dial or through a menu, they all work by altering just 5 settings in your camera: White Balance, Focus System, Shutter Speed, Aperture Value and Flash. Most cameras automatically control White Balance even in manual mode: you have to choose to override it, so I won't deal with it here beyond a brief mention.
[i]White Balance[/i] adjusts for the colour of the light falling on it. It mimics the human sight's tendency to see paper as white even if we turn off the fluorescent light and turn on the tungsten light…fluorescent is green, tungsten is red, yet the paper is still white to us.
[i]Focussing Systems[/i] move elements in the lens until the part of the subject in the focusing area is sharp. They can operate in various modes, the main ones being “single shot” which locks the lens as soon as focus is found; and “servo assisted” which attempts to keep the lens focussed on the subject as it moves. Other modes tend to be variations and combinations of these two.
[i]Flash[/i] is offered on most cameras and usually includes settings to reduce red-eye (reflections from the retina of the eye), general flash and some modes to allow “night portraits”, where a flash exposure to record the foreground is followed by a longer exposure to capture the darker background. Most cameras will also allow the flash to be disabled, and some cameras with a particular type of shutter will also allow you to choose whether the flash fires as the shutter begins to open, or as it closes.
The most important controls, however, are the Shutter Speed and Aperture settings. Understanding these two aspects of photography marks the difference between a snap-shooter and a photographer.
For this paper I want to focus on aperture. I will devote another paper to Shutter control. Once you have read both, you will never want to go back to “green box”, auto or any of the funny symbols again….well rarely. Instead, you will be master of The M, Tv, Av and P settings: manual, shutter priority, aperture priority and program mode.
Aperture Controls:
There are two settings on your camera which allow you to directly control the aperture of your camera but every manufacturer uses their own abbreviations for them. The first is the [i]Manual[/i] setting, which lets you change both the shutter speed and the aperture. It is almost always marked M or MAN. We won't be addressing Manual Mode today. The second is [i]Aperture Priority Mode[/i].
[i]Aperture Priority Mode[/i] is marked [b]Av[/b] on some cameras, on others, [b]A[/b], and on a few, [b]dep[/b], suggesting “depth of field control”. For convenience, I will use the term "Av". With the dial set to Av, you choose the aperture, and the camera automatically sets a shutter speed to provide the correct exposure. It can do this because the relationship between the aperture and the shutter speed is fixed: halve the aperture and you need to double the shutter speed to allow the equivalent amount of light to reach the sensor or film (from here on I will just refer to the sensor, but it applies equally to film). So what is this [i]aperture [/i]?
What is Aperture?
Originally, apertures were circles cut from pieces of thin material. My first camera was fitted with a metal plate in which different sized apertures were punched. To set the aperture, you slid the appropriate hole in front of the lens. Today a device called a "diaphragm" is used to control the effective diameter of the lens: inside each lens are a series of blades that can open or close. This lets the camera adjust the size of the hole that the light comes through when it enters the camera. The diaphragm produces and controls the aperture a lot like the iris of your eye. It is linked to the exposure meter and to the shutter, so that the shutter speed and aperture are linked when the camera is operating on anything but manual mode.
