What that "F“!
Lens Aperture Function
Most photographic lenses have a variable diaphragm opening; moreover, some with many stops in their opening range and others with few. To begin to understand what the diaphragm aperture is, we must first explain what the diaphragm is.
The diaphragm is a part of the lens that limits the entry of light towards the sensor of our camera. Then we have the opportunity to control the incoming light towards the camera by opening or closing the diaphragm first, then we can use other devices like filters as well.
There are lenses up to F / 0.95 of diaphragm opening. Now, what does the “F” mean? The letter “F” measures the light steps of the lens itself. For example, a lens could start with an aperture of F / 2.8 and go up to F / 20. The higher the “F” number, the tighter the aperture is. In contrast, the smaller the “F” number, the larger the aperture and the more light will enter the camera.
In the following image we will see the previous explanation clearer:
At the same time that we look for the focal length of the lens; we could find the minimum and maximum aperture as well. We must remember that the diaphragm aperture also helps us to obtain photos with a focused background or less depth to field, it also helps us to obtain an allusive bokeh. The more closed the diaphragm is, the more focused we will have our background.
Many professional photographers prefer to use bright, wide-diaphragm prime lenses such as the Canon EF 50mm f / 1.2L USM Lens for portrait work as they give a very elegant bokeh effect. On the other hand, a closed aperture between F / 11 – F16 are widely used for landscape photography as this provides very sharp background results.
Finally, the aperture of the diaphragm is a very valuable quality of our lenses. The lower the “F” number, the wider the diaphragm is and the more light enters the camera sensor. Also, the more open the diaphragm is, the more bokeh we could get. A very important fact is that very wide aperture lenses are considered “professional” or superior lenses and are consequently more expensive.