Photography Aperture

If you own a prosumer digital camera like the Canon Powershot or digital SLR like the Nikon D40, then you might be familiar with the term "aperture". The aperture is a hole or an opening in the digital camera lens through which light passes. If the aperture is narrow, then all objects in the digital camera lens will appear sharp and clear. If the aperture is wide, then only the item in focus appears sharp while everything is blurred.

Relation Between Aperture and Shutter speed

A photographer uses aperture in combination with shutter speed and iso to control the exposure of light. Typically, a fast shutter speed will require a larger aperture to ensure sufficient light exposure, and a slow shutter speed will require a smaller aperture to avoid excessive exposure.

The aperture works like the iris of the eye—it controls the diameter of the lens opening.

Many cameras allow you to shoot in aperture priority mode. Aperture priority allows you to choose an aperture setting so the camera decides the best shutter speed. This is also referred to as Aperture Priority Auto Exposure, A mode, Av mode, or semi-auto mode.

Aperture Is Measured In Fractions

The lens aperture is usually specified as an f-number, which is the focal length divided by the aperture diameter.

This means that an aperture f/1.4 will provide a larger lens opening than f/8. This took me time to understand but here's the math. Remember that aperture is a measurement of fractions! If f= 50mm, then f/1.4=35.7 and f/8=6.25.

A lens typically has a set of marked "f-stops" that the f-number can be set to. A lower f-number denotes a greater aperture opening which allows more light to reach the film or image sensor. To understand this concept better, I highly recommend Understanding Exposure: How to Shoot Great Photographs with a Film or Digital Camera by Brian Peterson.

Lenses and Maximum/ Minimum Apertures

The specifications for a given lens typically include the minimum and maximum apertures. These refer to the maximum and minimum f-numbers the lens can be set at to achieve. The maximum aperture (minimum f-number) tends to be of most interest; it is known as the lens speed and is always included when describing a lens. Here are a few examples:

• Canon EF-S 18-55mm f/3.5-5.6 IS SLR Lens
• Konica Minolta 28-100mm f/3.5-5.6 Maxxum D Series SLR Zoom Lens
• Nikon 24-85mm f/2.8-4.0D IF AF Zoom Nikkor Lens
• Pentax DA 50-200mm f/4-5.6 ED Lens
• Sigma 18-200mm f/3.5-6.3 DC Lens for Nikon Digital SLR Cameras
• Tamron AF70-300mm F/4-5.6 Di LD Macro Lens

A typical lens will have an f-number range from f/16 (small aperture) to f/2 (large aperture) (these values vary). Professional lenses for digital cameras can have f-numbers as low as f/1.0, while professional lenses for some movie cameras can have f-numbers as low as f/0.75 (very large relative aperture). These are known as "fast" lenses because they allow much more light to reach the sensor and therefore reduce the required exposure time.

Lenses which have a fixed focal length (FFL) and large aperture are favored especially by photojournalists who often work in dim light, have no opportunity to introduce supplementary lighting, and need to capture fast breaking events.

Zoom lenses typically have a maximum aperture (minimum f-number) of f/2.8 to f/6.3 through their range. A very fast zoom lens will be constant f/2.8 or f/2, which means the relative aperture will stay the same throughout the zoom range.

Here are a few examples of digital camera zoom lens:

• Nikon 70-300mm f/4.5-5.6G ED-IF AF-S VR Zoom Nikkor Lens
• Canon EF 28-135mm f/3.5-5.6 IS USM Standard Zoom Lens
• Sigma 70-300mm f/4-5.6 DG Macro Telephoto Zoom Lens for Canon SLR Cameras
• Tamron 18-250mm F/3.5-6.3 AF Di-II LD Aspherical (IF) Macro Lens for Nikon Digital SLR Cameras
• Tamron Autofocus 75-300mm f/4-5.6 LD with Hood for Canon SLR Cameras