What is focal length?

[Peter_S.]

Focal length is the distance from the centre of the lens to the image sensor (focal plane), and each lens has a different focal length.
Focal length is important since it determines the range of a scene you can capture (angle of view). As shown in the following photographs, the shorter the focal length is, the wider the range you can capture, while the longer the focal length is, the more distant objects appear larger.

(*) The relationship between focal length and angle of view varies depending on cameras. The explanation in this Shooting Guide is based on APS-C format cameras, unless specified otherwise.

Generally, lenses with a focal length of around 35 mm are called "normal lenses" as they have an angle of view close to the human visual field. Lenses with a focal length shorter than this are called "wide-angle lenses," and those with a longer focal length are called "telephoto lenses." However, there are no strict standards for these terms. Use different lenses according to subjects or images you want to shoot.

Let's check the focal length of your lens. The range of the focal length available with the lens is printed on the lens. For example, the focal lengths from 55 mm to 200 mm are available with SAL55200-2 in the picture below.
Also, on the mount side of the lens barrel (near the camera body), you can see the mark for the focal length currently set. In the picture below, the current focal length is 55 mm.

In this picture, "55-200" on the left side is the range of the focal length available with the lens. The white line on the right side indicates the focal length currently set.

Zoom lenses and fixed focal length lenses

Lenses are divided into two types: “zoom lenses” with a variable focal length and “fixed focal length lenses” with a fixed focal length. Some zoom lenses are versatile and adjust from wide angle to telephoto by themselves. As well as being useful for everyday shooting, these lenses are especially convenient for travelling, as you'll want to reduce your amount of baggage as much as possible.

On the other hand, if you use a fixed focal length lens, which does not have a zoom feature, you need to move by yourself to determine the composition. However, fixed focal length lenses are usually faster and have a wider aperture, and have advantages in the expression using defocused backgrounds and the ability to use high shutter speeds in low-light situations, reducing image blurring. In addition, with superior rendering performance, you can enjoy excellent image quality that cannot be delivered by a zoom lens.

This photograph was shot with a fixed focal length lens. By setting the aperture to a small f-number, the background is defocused to a large degree.
Macro lenses, which allow you to take close-ups by getting closer to a subject, are also fixed focal length lenses. Although many recent zoom lenses have the macro feature with fairly short focusing distance, their performance cannot match that of a dedicated macro lens.

This photograph captured the details of a sunflower with a macro lens. With a macro lens, you can get this much closer to your subject.