Aperture is one of the three basic controls in photography used to control light. Working with shutter speed and film speed, aperture completes the exposure triangle to allow us control over the light that is captured by the camera. Unlike shutter speed and film speed, aperture is actually within the lens rather than the camera body. Aperture also has a secondary function of changing the depth of field of a photograph.
What is Aperture
Aperture refers to an adjustable opening inside your camera lens. This opening adjusts from large to small much like the pupil of your eye. When the aperture is small, like your eye’s pupil in bright light, less light reaches the film or digital sensor of your camera. When the aperture is wide, like your eye’s pupil at night, more light is allowed to travel through the lens and strike the film or digital sensor in the camera.
How is Aperture Controlled
Aperture is controlled using the F-Stop settings on your camera. F-Stop is a fractional representation of the aperture compared to the focal length of the lens. Basically, F-Stop means “focal length stop.” That’s quite a mouthful so like most terms, it was shortened to F-Stop way back in the history of photography.
Like shutter speed, the numbers on the F-Stop display or dial are the numerator of the fraction. That means that just like 25 is a bigger number than 100 on your shutter speed readout (1/25 and 1/100), f2.8 is a bigger number than f11 (1/2.8 and 1/11 in very simplified terms for comparison’s sake).
Don’t worry yourself needlessly with trying to remember all of the math or theory behind aperture and F-Stop while you are just starting out. Until it becomes second nature, just think of it this way:
Big F-Stop Number = More Light Needed = More in Focus
Little F-Stop Number = Less Light Needed = Less in Focus
For a full explanation of aperture’s effect on depth of field (amount of your photo in focus), please see the photo lesson on depth of field.
If your camera does not allow you to set the aperture or F-Stop you may need to work with the preprogrammed modes to get the aperture you wish to use.
Aperture Priority – Lets you to set the aperture and the camera determines shutter speed and ISO
Landscape Mode – Uses a smaller aperture (large F-Stop)
Portrait Mode – Uses a larger aperture (small F-Stop) and slow film speed
Because aperture is controlled by a mechanical device, there are limits to the adjustment capabilities. These limits vary from lens to lens as well. The smaller the lowest possible F-Stop, the lower the light conditions the lens can be used in. Lenses with lower F-Stop capabilities are referred to as fast lenses because they can shoot at relatively fast shutter speeds in low light.