The aperture regulates the amount of light that hits the sensor. If the aperture is fully open, a lot of light is allowed through. The more closed the aperture is, the less light is allowed through to hit the sensor. The aperture is mostly a mechanical system that consists of circularly arranged blades which slide over each other to let in either more or less light.
There is sometimes some confusion when talking about the aperture since there are several different types of notation.
Basically, the aperture value is represented as a fraction, a so-called f-number. This is given as either 1 / f-number or f / f-stop. Some camera manufacturers only specify the aperture value on the lens.
The following is the standard full-stop f-number scale:
1 | 1.4 | 2 | 2.8 | 4 | 5.6 | 8 | 11 | 16 | 22 | 32 | 45 | 64 | 90
Usually, normal lenses have a maximum aperture value of 22, but some special lenses are capable of higher aperture values.
When speaking of an aperture value of 4, the real value is actually 1/4 or f/4. The representation of the aperture value as a fraction simplifies the understanding of the aperture. Just as is known in mathematics, the larger the denominator, the smaller the overall number is. 1/16 is a smaller number than 1/4. Likewise, the larger the f-number is, the less amount of light is allowed through the aperture. An aperture value of 16 means the aperture is much more closed than an aperture value of 4, meaning less light is allowed to pass through the aperture.
Important to remember:
- Aperture value = 1 / f-stop
- The smaller the aperture value, the less amount of light is allowed through the aperture
- The larger the aperture value, the more amount of light is allowed though the aperture
You should choose a fitting aperture value depending on the amount of ambient light available. If less light is available, you should use a larger aperture value in order to let in the most amount of light through the aperture as possible to hit the sensor. If there’s a lot of light available, on the other hand, you can use a smaller aperture value. When using a smaller aperture value, the aperture is more closed and lets less light through to hit the sensor. By selecting the right aperture value, you can avoid under- or overexposed photos.
The choice of which aperture value to use influences other factors in photography as well. If you choose a larger aperture value (i.e. an aperture with a smaller f-number), then the aperture is wide open. Accordingly, this allows more light to hit the sensor, which makes it possible to use a shorter exposure time. If you use a smaller aperture value, less light is allowed through to hit the sensor, which means a longer exposure time is necessary to produce a good result.