Focal length refers to the distance from the center of a lens to the image sensor (focal plane), and every lens has a distinct focal length. Focal length is critical because the range of the scene you can capture (field of view) is determined by this value. As shown in the sample photos: the shorter the focal length, the wider the shooting range; the longer the focal length, the larger distant objects appear. Kaimorui brings you the introduction below.

Note: The relationship between focal length and field of view varies from camera to camera. Unless otherwise specified, the information in this guide applies to APS‑C format cameras.

Generally speaking, a lens with a focal length of around 35 mm is known as a standard lens, as its field of view approximates human vision. Lenses with shorter focal lengths are wide‑angle lenses, while those with longer focal lengths are telephoto lenses. There are, however, no rigid boundaries between these categories. Select different lenses according to your subject or desired image effect.

Now let’s take a look at the focal length marked on your lens. The supported focal length range is printed on the lens barrel. For example, the SAL55200‑2 lens shown in the figure has a focal length range of 55 mm to 200 mm. On the mounting side of the barrel (near the camera body), you can also see the marker indicating the currently set focal length. In this example, the current focal length is 55 mm.

In this illustration, “55‑200” on the left stands for the lens’s available focal length range, and the white line on the right marks the current focal length setting.

Zoom Lenses vs. Prime Lenses

Lenses fall into two categories: zoom lenses with variable focal lengths, and prime lenses with fixed focal lengths. Some zoom lenses cover a broad range from wide angle to telephoto. They are highly practical for everyday shooting and especially convenient for travel, helping you pack lighter.

By contrast, with a prime lens that has no zoom capability, you adjust framing by physically moving your position. Prime lenses, however, usually feature faster speeds and larger apertures. They are ideal if you want blurred background bokeh, or need a faster shutter speed in low‑light conditions to reduce motion blur. In addition, prime lenses deliver superior optical performance and image quality that zoom lenses cannot match.

This photo was taken with a prime lens. When the aperture is set to a small F‑number, the background exhibits strong bokeh.

Macro lenses, used for close‑up shooting near the subject, are also prime lenses. Although many modern zoom lenses offer macro functionality with a short minimum focusing distance, their performance still cannot compare with dedicated macro lenses.

This photo captures fine details of a sunflower using a macro lens. A macro lens allows you to get much closer to your subject.