What is a zoom lens?

When selecting lenses for mirrorless or DSLR cameras, you have two broad categories of lens options. The first is a prime lens, which provides a single focal length that cannot be adjusted. Another category is zoom lenses, which allow manual adjustment of a range of focal lengths. This article will introduce what a zoom lens is and some information about it. 

1. What is the zoom lens?

A zoom lens is a camera lens that can change the focal length in a certain range, so as to get different widths and narrow field angles, different size images,s and different scopes of scenery. Zoom lenses can change the shooting range by changing the focal length without changing the shooting distance, so it is very conducive to picture composition. Because a zoom lens can serve as several prime lenses, traveling not only reduces the number of photographic equipment but also saves the time to change lenses.


2. What is the history of zoom lenses?

The forerunners of today’s zoom lenses date back to the 1830s when they were components of optical telescopes. Zoom lenses began to be used in cameras in 1902 when Clive C. Allen invented the zoom lens for motion pictures. But it wasn’t until the 1920s that zoom lenses became more widely used in movies. Film legends such as Orson Welles and Alfred Hitchcock popularized the use of zoom lenses in film, which led to the further development and enhancement of zoom lens technology in film and photography.

Zoom lenses are still widely used in today’s mirrorless and digital SLR cameras, and they can improve image quality in both all-light and low-light environments.

3. Zoom principle of the zoom lens

Optical zoom is to move the lens inside the lens to change the focus position, change the length of the lens focal length, and change the size of the lens angle, so as to achieve the image magnification and reduction. In the image above, the long right side of the red triangle is the focal length of the camera. When you change the position of the focus, the focal length changes.

For example, by moving the focus in the opposite direction of the image, the focal length becomes longer and the angle of view in the image becomes smaller. In this way, the view area becomes larger on the image plane.

4. What are the advantages of using a zoom lens?

Zoom lenses offer many advantages to both professional and amateur photographers. Most of this has to do with focal length adjustment, but there are many other advantages.


(1) Versatility

Unlike prime lenses, zoom lenses offer multiple focal lengths in a single component.

(2) Artistic possibilities

The zoom lens allows you to zoom in on images and crop out unwanted themes.

Visual resolution. If you can choose a top-notch zoom lens, you may find that the sharpness is very similar to that of a prime lens.

(3) Can change the focal length during the journey

Adjusting the focus allows you to continue shooting without having to mount and remove the lens from the camera body.


(4) Post photography digital zoom

Optical zoom lenses allow you to take photos at different focal lengths while maintaining the maximum resolution your camera lens allows. Analog with digital zoom cannot match the quality of photos taken with an optical zoom lens.

5. Classification of the zoom lens

According to the size, the camera lens is divided into a box lens and a portable lens. In theory, box lenses have larger lenses and better optical properties than portable lenses. The focal length of the box lens can be changed and focused only by changing and focusing the servo handle, while the portable lens can be changed and focused manually or servo-operated by switching on the lens.


According to zoom range, the camera lens can be divided into the wide-angle lens, standard lens, and telephoto lens. Focal length is a basic feature of the lens, which determines the magnification of the image and the horizontal field of view taken by the lens.

Focal length is determined by measuring the distance from the optical center of the lens to the point at which light rays converge behind the lens to produce a sharp image, which in the case of a television camera is the CCD target. The shorter the focal length, the wider the horizontal field of view, and thus the smaller the image. The horizontal field of view narrows as the focal length increases, while the subject grows larger.

6. What is the difference between optical zoom and digital zoom?

The main difference between optical and digital zoom is that while optical zoom involves a physical mechanism to change the focal length of the lens, digital zoom has no physical component. It is a software operation that measures the increase in focal length of the lens when measuring optical zoom. The farther away the lens is from the camera’s image sensor, the greater the zoom.


Digital zoom is not easy to measure. One digital camera manufacturer’s digital zoom specs may differ from another’s specs. Digital zoom works by cropping an existing image and zooming in on whatever is in the center of that image. The physical lens itself maintains a fixed focal length; in other words, it acts as a prime lens.

Digital zoom requires the removal of pixels from larger images, which reduces the overall quality of the photo. If you need to use digital zoom, keep in mind that it works best on extremely high-resolution photos. If the resolution is low to start with, digital scaling can quickly make your photos grainy and visual.


What is a zoom lens used for?

A zoom lens is an SLR or DSLR lens that offers a different focal length for the photographer to select from. The zoom lens can be manually adjusted by the user to create a focused image at a wide distance from the subject.

What is considered a zoom lens?

A zoom lens is a mechanical assembly of lens elements for which the focal length can be varied, as opposed to a fixed focal length lens. A true zoom lens also called a parfocal lens, is one that maintains focus when its focal length changes.

Is a prime lens better than a zoom?

Generally speaking, prime lenses are sharper than zoom lenses of comparable focal lengths. This is because zoom lenses have extra glass inside that has to move in order to shift the focal length, causing some diffraction. Still, these days there are many excellent and very sharp zoom lenses on the market.

How does lens zoom work?

An optical zoom lens works the same way as any other lens, except it has a system with moveable glass pieces that can shift around to give the lens different focal lengths. When you change the focal length, it also changes the field of view of the image.

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