Among the elements to consider, when analyzing the specifications of photographic sensors, there is the so-called F-Stop also called focal ratio. This is a very important parameter for evaluating the opening of a goal and, therefore, the ability to “let in the light” and be able to obtain satisfactory shots in all conditions of use. Analyzing the F-Stop value, in photography, is essential to know the characteristics of the sensor and understand how to best use it.
As for smartphones, where the photographic sector becomes increasingly important and articulated, F-Stop is one of the main elements to consider when analyzing the camera specifications. Even more than Megapixels, a single real-time parameter for judging a camera, this parameter must be analyzed and can offer precise indications regarding the ability to take good photos, particularly in low light conditions.
When you want to take beautiful photos with your smartphone it is necessary to go into the details of the specifications, evaluating all the elements of the photographic sensors and also considering the software optimization, which is increasingly important for “mobile photography”. Furthermore, given the limited dimensions of the sensors, it is appropriate to exploit the best accessories for taking pictures with your smartphone to maximize the yield of their shots.
Here is what is meant by F-Stop and how this parameter affects the performance of a sensor of a traditional camera or a smartphone.
Exposure
The main element that determines the rendering of a photograph is exposure. This is a measure of the amount of light that reaches the camera’s sensor. If the incoming light is not optimal, the shooting result may be poor. If the photo is too bright it is defined as “overexposed” while if it is too sorry it will be “underexposed”. Finding the right balance between the various factors at play is essential to obtain good results.
Three parameters come into play to influence the exposure of a photo. The first element is the opening, or diaphragm, which indicates the size of the aperture of the lens diaphragm. As we will see, the F-Stop refers precisely to this element. The second element is the exposition time which is a measure of how long the shutter remains open. The third element is the light sensitivity of the sensor. This parameter is indicated by the term ISO.
These three elements make up the so-called “Triangle of exposure”. The main job of a photographer is to find the right balance between these parameters, based on the camera he is using, the subject to be photographed, and the brightness of the environment. Digital cameras, as well as smartphones, can automatically manage the three parameters to optimize shots.
The concept of Stop in photography
Another fundamental element to understand what is meant by F-Stop is related to the “Stop” concept in photography. From the theoretical point of view, the Stop is considered as the interval between an exposure value and the previous or next value. This is a central aspect of the entire shooting process.
Increasing one Stop means doubling the amount of light that reaches the sensor of your camera. Decreasing it by one, on the other hand, means halving the amount of light. In general, it is possible to adjust the Stop and, therefore, the amount of light by intervening on the various parameters of the “exposure triangle”. By adjusting these parameters you can get the shot you want.
What is the F-Stop parameter?
The parameter plays a very important role in defining the technical specifications and, therefore, the behavior of a photographic lens F-Stop which is expressed as f / n where n is a number. This is the relationship between the focal length of a lens and the aperture of the lens (the hole in the lens through which light enters) and is a very important element in identifying the right exposure of a photo. This parameter is also called the focal ratio.
Having an F-Stop equal to f / 2 means having an aperture equal to half the focal length. If the focal length is 100 mm then, in the case of off / 2, the aperture will be equal to 50 mm (i.e. 100/50 mm). An f / 2 lens with a focal length of 200mm will have an aperture of 100mm. The two sensors, despite having different focal lengths and aperture, will get the same incoming light as the F-Stop value is the same.
The transition from an f / 4 to an f / 2 does not mean doubling the amount of light entering the sensor as the F-Stop value does not follow a linear but logarithmic scale. With this passage, in fact, the light entering the camera is quadrupled. In principle, therefore, as the n value of the f / n parameter increases, there will be a reduction in the amount of light arriving at the sensor.
A lens with a low focal ratio, such as f / 2, is referred to as “fast”. Similarly, a high focal ratio lens, such as f / 12, is called “slow”. To take a very bright photo it will be necessary to open the aperture and have a low F-Stop. This choice results in a reduction of the depth of field and, therefore, only part of the scene will be focused correctly. To bring the background into focus, you will need to close the iris, reducing the amount of light entering the sensor.
To find the right balance, it will be necessary to intervene on all parameters, optimizing exposure time and ISO to obtain the desired shot. The photographer can manually manage these parameters to adapt the camera’s rendering to the shooting conditions. Alternatively, with an active automatic mode, the camera sets the parameters necessary to obtain a good result from the images taken.
F-Stop and smartphone photography
On cameras, even non-professional ones, there is the possibility for the user to adjust the F-Stop value to adapt it to their needs. The adjustment can be done manually, thus leaving the photographer the possibility to adjust the behavior of his camera according to the various conditions in which the shot is made.
Photography applied to the smartphone sector involves several trade-offs, even for simple reasons of space. The photosensors of smartphones have very small dimensions. In most cases, the opening is fixed and users do not have the possibility to modify this parameter. In the technical data sheets of the smartphones, next to each sensor a very precise F-Stop value is shown, for example, equal to f / 1.6 or f / 1.8.
The evaluation of sensor opening is an important element though it is not the only aspect to consider to judge the photographic performance of a smartphone. A lens with a large aperture, all other things being equal, will be able to guarantee better performance in low light conditions and will be able to count on a faster shutter speed. On mobile devices, the software optimization, able to better manage the shots and set the exposure conditions according to the needs of the moment.
Users, on most smartphones, have the possibility to intervene on parameters such as the ISO thanks to the manual mode (often called Pro). In this way, you can adjust the behavior of the photosensor you are using your experience to create the shot you want. The options available to the user are more limited than with traditional cameras.