Focal length, a whole program… When one starts in photography, as in many other fields, one does not escape this step: learning, reading and writing about the subject. Before jumping into a new passion, each aspiring enthusiast must familiarize himself with a specific vocabulary and the matching concepts. The future photographer is not spared and he will be obliged to integrate some basic notions that will allow him to better understand photography in his practice and help him to obtain better results. I am not a supporter of the application of technique in its purest definition but I must recognize that some principles are elementary if one wants to progress. This is the case of the one we will discuss today: the focal length of a lens.
What is the focal length?
The focal length of a lens can be defined as the distance in mm that exists between the focal plane of the sensor and the optical center of the lens. That was a bit stodgy, wasn’t it? More simply, the optical center is like a point inside a lens through which light rays pass, intersect and are directed to the image sensor of your camera to record the photograph and allow it to appear. This optical center is always very close to the diaphragm of the lens.
For this reason, this millimeter value is the first characteristic used by photographers to define the different lenses. We speak of a 50 mm or an 8 mm, for example.
So what effect do different focal lengths have on the same image? The smaller the focal length, the larger the angle of view of the lens, thus increasing the size of the scene we see. The longer the focal length, the smaller the angle of view, thus reducing the size of our photograph. For this reason, as you can see below, the use of a telephoto lens can create a feeling of compression of the scene or frame (very interesting for the foreground), while using a wide angle lens gives the feeling that the scene is enlarged, allowing more elements to enter the frame.
This is why we will see later that using telephoto lenses, we have the impression that the scene and the frame are compressed (they are the most suitable for successful first shots). On the contrary, using a wide angle lens gives us the feeling that the scene is expanding with more elements inside.
Angle of view
The angle of view of a lens is a technical characteristic that manufacturers provide for each model of lens, but what does it really mean?
The angle allows us to determine the field of view of the lens and thus determine the number of elements that can enter our frame. This concept allows us to classify lenses according to different categories, which you probably know:
Let’s start with the wide angle lenses, which include focal lengths smaller than 35 mm and capable of capturing images with an angle of vision greater than the human eye (without taking into account the peripheral vision), ie, more than 63º of the visual field.
If we want to go a little deeper, we could also consider wide angle lenses whose focal length is between 10 mm and 14 mm and fisheye lenses (whose name refers to the type of vision characteristic of fish) and those whose focal length is below 9 mm…