Chooza Blog

The difference between a fixed focal length lens and a zoom lens is that with zoom lenses a photographer can vary the focal length within a pre-defined range. Zoom lenses make it much easier to produce a number of different perspectives or compositions, as it removes the requirement for lens changes. This is particularly important when photographing dynamic subject matter. When utilising a zoom lens a photographer will still need to change their position, as in fact the zoom lens just allows for improved flexibility.

A zoom lens is a combination of lens elements that provides the ability to vary its focal length. Zoom lenses are most often used with still, video and motion picture cameras. They can also be used with projectors, some binoculars, microscopes, telescopes, telescopic sights and other optical instruments. A true zoom lens is also known as a parfocal lens, as it maintains focus when its focal length changes. There are a wide range of zoom lenses, some are telephoto, some are wide-angle and there are others which cover a range from wide-angle to telephoto.

Zoom lenses are often described by the ratio of their longest to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or “4×” zoom. The term “superzoom “or “hyperzoom” is used to describe photographic zoom lenses with very large focal length factors, typically more than 4× and ranging up to 15× in SLR camera lenses and 26× in amateur digital cameras. This ratio can be as high as 100× in professional television cameras.

Many of today’s modern digital cameras have features which allow the cropping and enlarging of a captured image. These options are designed to simulate the effect of a longer focal length zoom lens. This is commonly known as digital zoom and produces an image of lower optical resolution than optical zoom.

An optical zoom is a true zoom, as the focal length changes and the zoom mechanism itself extends and retracts, so that an image is magnified by the lens itself and therefore an optical zoom produces the best quality images.  A digital zoom however is not a true zoom but a simulated zoom that enlarges the central portion of an image in the camera. The actual length of the lens does not change, which is why digital zoom lenses produce images with reduced visual quality.

The internal construction of all zoom lenses is very complex and contains a wide variety of large and small parts. In fact, zoom lenses are usually made up of well over one hundred individual parts.

A conventional zoom lens is normally made up of three specific moving optical groups plus one stationary optical group, with each optical group containing two or more lens elements but many actually contain substantially more.

Within a zoom lens there are generally three independently moving groups of optical elements and one stationary group of optical elements. Some zoom lenses actually move all four optical groups when the lens is zoomed. These four optical groups are the focus, variator, compensator and master group.

The focus group moves forward or backward as necessary for focusing and zooming the lens. The variator group changes the magnification power of the focus group and is responsible for changing the focal length of a zoom lens when it is zoomed. The main purpose of the compensator group is to maintain correct focus whenever the zoom lens is zoomed. The variator and compensator groups work in tandem to create the change in focal length when the lens is zoomed, and the compensator group also ensures that the lens remains in focus while being zoomed. The master group relays the optical path to the camera’s focal plane and also enables the zoom lens to be more compact.

However certain zoom lenses, particularly very wide angle to moderate telephoto zooms, actually move all four optical groups as the lens is zoomed, meaning that every optical group in these is part of the overall zooming function and may perform more than one function.

Zoom lenses feature extremely complicated internal construction, as not only must the various optical groups have the correct rate of movement, but this must also be done precisely while maintaining optical alignment of the optical elements. This movement is achieved via a series of nested barrels or sleeves, which feature machined cam-slots and cam-followers.

The challenge for optical engineers is to optimise the lens by combining optical elements using a wide range of options to create lenses that perform exceptionally well.

There are a wide variety of different camera lenses for digital cameras. These range from very small, inbuilt, fixed focal-length plastic lenses to large, glass, removable zoom lenses with special optical coatings. The final design of each camera and the features available are affected greatly by the type of lens used.

There are four main categories for digital camera lenses and these are fixed-focal length, retractable zoom, fixed zoom and interchangeable lenses.

Digital cameras using a fixed-focal length lens do not provide optical zoom but this does allow for compact camera design. The benefits of this type of camera are that they are relatively cheap, fast and simple to use and generally offer a wide angle view. However, these cameras are generally quite poor when it comes to actual optical quality, they struggle to zoom in on objects in the far distance and the lens itself is rarely adaptable for filters or converters. This type of camera is ideal for children learning to use their first camera or people looking for a basic device.

The difference between digital cameras, which use a retractable zoom lens, is that the zoom lenses extend when the camera is switched on and retract into the body of the camera when switched off. The benefits of this type of lens are that the lens is generally protected by a built-in cover and it allows for very compact, portable camera design. However this type of lens usually has a limited zoom range, does not support filters or converters and the ability to adjust focus manually is often restricted. This type of camera is ideal for the design conscious or for those looking to take basic snaps of friends, family and trips away.

Fixed zoom lenses are attached to the body of the camera and do not retract when the camera is switched off. Again this type of lens is generally protected by a built-in cover and allows for compact, portable cameras. However, it suffers from the same disadvantages as the retractable zoom lens, in that it usually has a limited zoom range, does not support filters or converters and the ability to adjust focus manually is often restricted. This type of camera is therefore ideal for those looking for a cool gadget or that have a restricted budget.

The main benefit of using an interchangeable lens is that it can be detached from the body of a digital SLR camera and replaced with any other compatible lens.  This type of lens produces the best optical quality, provides a good degree of flexibility and the lens can be upgraded without the need to purchase a new camera. However, these types of lenses are bulky, expensive and demand some photographic expertise.  This lens is most suitable for an experienced photographer looking to develop their skills and take it to the next level.