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The light intensity of lenses is an important factor in photography, as it influences how much light the lens allows to fall on the image sensor
This is behind the light intensity of lenses
The speed is referred to as the f-number or aperture value and is indicated by a number after the letter “f”, such as f/2.8 or f/1.4:
- The f-number, also known as the “f-value”, indicates the ratio of the focal length to the diameter opening of the aperture. The smaller the f-number, the larger the aperture opening and the more light can pass through the lens.
- A lens with an aperture value of f/1.4 therefore lets more light through than one with f/2.8. This is particularly advantageous in low light conditions, as it makes it possible to use shorter exposure times or work with a lower ISO sensitivity.
- In addition to the amount of light, the f-number also influences the depth of field, i.e. the area in the image that is in focus. A small f-number (e.g. f/1.8) produces a shallower depth of field, which means that the main subject is in focus but the background is blurred.
- This effect is often used in portrait photography to emphasize the subject. A larger f-number (e.g. f/16), on the other hand, increases the depth of field so that more areas in the image are in focus, which is an advantage in landscape photography, for example.
Importance for the selection of the lens
The f-number of a lens therefore provides information about its light intensity, the amount of light transmitted and control over the depth of field. These factors are decisive for choosing the right lens:
- When a lens is described as “fast”, this means that it has a small f-number such as f/1.4 or f/2.0.
- Such lenses are usually more expensive and larger, but offer flexibility in low-light photography and allow creative design possibilities through shallow depth of field.
- Lenses with higher apertures such as f/4.0 or f/5.6 are often more compact and less expensive, but less suitable for low-light photography without additional lighting.
