In the first article of our series on mobile photography we had to talk about wide angle lenses, and now we will take a very similar path although in the opposite direction. We return to the concept of focal length although instead of using it to our advantage to move objects away, what we now have to do is bring them closer.
That is basically the meaning of a telephoto lens or a telephoto lens, depending on what we decide to call it. A telephoto lens is anyone who brings objects closer to us without software tricks, simply by using your own optics. And although the most purists decide not to consider it that way, they are responsible for the fact that many phones today already have optical zoom as one of their multiple camera options.
Focal length and telephoto lenses
As we said in the introduction, it is time to return to the concept of the focal length, although now to zoom in instead of zoom in. We said that the focal length was the distance in millimeters (or equivalent) between the optical center of the camera and the photographic sensor. In this case, the sensor located at the heart of the mobile phone.
The difference is that here we no longer speak of focal lengths less than 35 millimeters, or 18 millimeters when we speak of super wide angles, but to greater than 35 millimeters. In fact, on mobile phones it is often referred to as a telephoto lens above 50 millimeters although in more traditional cameras we usually find them flying above 70 millimeters and reaching insane lengths of up to four figures. Right, Nikon Coolpix P1000 that reaches 3,000 millimeters?
We say that on mobile phones, anyone who exceeds 50 millimeters is usually treated as telephoto because the use in mobiles is to offer fixed optical zoom (we will see later that there are other options on the market). This means that the main lens of the phone is taken as a reference and multiplied, so if our phone has a 26-millimeter lens (very common), the telephoto lens in charge of giving us optical zoom will have 52 millimeters (two magnifications), 78 millimeters (three times), etc.
Super wide angle
Samsung Galaxy S20 +
29 mm (1.1X)
Sony Xperia 1 II
70 mm (3X)
Xiaomi Mi 10 Pro
50 mm (2X)
88 mm (3.7X)
OPPO Find X2 Pro
129 mm (5X)
Huawei P40 Pro
125 mm (5X)
iPhone 12 Pro
52 mm (2X)
As we can see, the concept is quite simple. Below 35 millimeters we zoom out the image, above 50 millimeters we bring it closer. And between 35 and 50 millimeters we find a terrain that is rarely explored with fixed lenses (yes with telephoto lenses) in which what we photograph is captured more or less at the distance and real size. Always nuanced, of course.
Not everything is millimeters, there are also degrees
When we talked about the wide angles we also made reference to the curvature of the lens itself, which ultimately gives the lens its name. « Wide angle » is a lens that moves between 60º and 120º of curvature (180º are already fish eyes). At telephoto lenses, angles drop dramatically. Looking at traditional lenses, we come across 30º for 80-millimeter objectives, or 24º for 100-millimeters. And the lens flattens more and more the greater the focal length.
The peculiarities of telephoto lenses and moving type
We have already said that telephoto lenses bring the image closer to us and that is what defines them, but they have some peculiarities that are worth knowing when using them correctly for the photograph we are thinking of capturing. Depth of field is shallow for telephoto lenses, narrowing more and more the longer the focal length is. This means that the area in focus in front of us is reduced and the background detaches more and more from the foreground as the millimeters increase. Hence telephoto lenses are often used in portrait photographyThe sensors that come with these lenses have less trouble separating the foreground from the background and the natural bokeh of the lens is greatly increased.
In mobiles, the telephoto lens is usually in charge of depth readings due to its ease of identifying funds
In fact, these lenses are usually in charge of depth readings on mobiles. And since we are talking about multiple lenses, why not talk about the different types of optical zoom that we find in mobile phones thanks to telephoto lenses. We said that the focal length of the main lens is usually multiplied in order to offer the zoom, and we have optical zoom of two, three and up to five times when we observe, and this is done with fixed lenses but now there are also mobile ones.
There is already a product on the market, such as the OPPO Reno 10X Zoom, which has a moving lens inside. The system is quite ingenious because the camera has a prism inside that, when rotated, allows the image captured by the lens to be focused or dispersed, so that it is enlarged or reduced. Thus, with a fixed lens we obtain mobile optical zoom and, therefore, adjustable. A breakthrough for mobile phones, which in the future could perhaps solve all photographic modes with a single camera or, at least, reduce the number of those that already exist.
And so far what we have to tell you today about telephoto lenses. And as we did with the wide angles, what better way to close than with a quick and clear summary of what these lenses are like that we already find in many mobile phones. Long focal length, narrow angle of view, shallow depth of field. We read each other in a week.