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Digital cameras - Zoom lenses and prime lenses explained

By Edited Nov 13, 2013 0 0

Strictly speaking, there are two types of lenses that are used in the world of photography and are available to the photographer, and these types of lenses are the zoom lens and the prime lens. However, in reality these broad brush classifications are broken down even further. Essentially, both zoom lenses and prime lenses serve the same basic functions. Both zoom lenses and primes lenses are used wide open to create creamy smooth bokeh and a blurred background. When combined with a fast shutter speed both zoom lenses and prime lenses are used to freeze motion. In order to achieve front to back sharpness both zoom lenses and prime lenses are stopped right down to a narrow aperture. Even though both types of lenses are used in the same way to achieve the same effects there are differences between the two types of lenses.

There is an ongoing argument that using a prime lens will result in sharper pictures with better optical quality than when a zoom lens set at the same focal length. Whilst this may be true when comparing a prime lens and zoom lens in the same budget, i.e. with the same quality optics, materials etc., it is not always true when comparing a high-end zoom lens with a lower end prime lens, although this is to be expected. In reality the differences in optical quality between a high-end zoom and a high-end prime are only really noticeable at the extremes, i.e. when the lens is wide open or closed right down. Between the two extremes the difference is negligible and given that many photographers don’t use the extremes it should not be too much of an issue. In reality, the difference in optical quality is likely to go unnoticed by all photographers other than the ’professionals’ or those serious (and finicky) enthusiasts.

The panasonic Lumix 14mm F2.5 prime lens on the left handside is photographed next to the Olympus 14mm - 42mm zoom lens. It is easy to see the prime lens is much smaller and when put on to the camera makes a portable solution that can easily fit in any jacket pocket.

A prime lens and a zoom lens side by side

By their very nature and the way in which they are manufactures all prime lenses will have a constant maximum aperture, ‘F’ number. This is advantageous since once the photographer has set the correct exposure, since it can be locked in and used for multiple photographs. It is possible to get zoom lenses with a constant maximum aperture throughout the focal range or different maximum apertures at different focal lengths. For example, a Canon 70mm – 200mm F4L IS USM lens has a constant maximum aperture throughout the full focal length whereas a Canon 75mm – 300mm F4.5 – 6.3 has a maximum aperture of 4.5 at the wide end, i.e. 75mm, but a smaller maximum aperture of 6.3 at the zoom end, i.e. 300mm.

The Canon EF70mm - 200mm F4L IS USM zoom lens. This is another cracking Canon lens that is used by many professional photographers. This zoom lens is one of the best. It is sharp and can produce some amazing images. The image stabilisation technology helps to ensure pin sharp images every time.

The Canon EF70mm - 200mm

When using a zoom lens with a constant maximum aperture the photographer will have the same benefits if a prime lens is used in that the exposure can be locked so it is the same throughout all focal lengths. If the maximum aperture is variable and changes throughout the focal lengths the advantage will be lost and the photographer is likely to need to tweak the camera’s settings at the different focal lengths in order to achieve the same exposures. This is not such a big issue in the studio where the photographer has time to tweak the shot and ensure everything is perfect before the shutter button is pressed but in the field it is a different story, especially if shooting fast moving objects at different focal lengths.   

The Canon EF24mm - 70mm F2.8L zoom lens. This is an awesome professional grade lens that is capable of some stunning images. The EF24mm - 70mm zoom lens is the work horse of many professional photographers. It is not the cheapest of lenses but it is worth every single penny.


The canon EF24mm - 70mm F2.8L zoom lens

As its name suggests a fixed length prime lens has a single fixed focal length that cannot be changed. The only way to increase, or indeed decrease the amount of frame the subject takes up is to physically move backwards and forwards, which may not be possible in specific circumstances. For example, if the photographer is standing right at the front of a safety fence shooting caged animals at a zoo and wants to get the subject larger in the frame he is going to be out of luck as it is not possible to move any further forward. Alternatively, if the photographer may be stuck in a crowd of people, at a music festival or gig for example, and not have the opportunity to move forwards or backwards in order to change the composition of the shot or get the subject larger or smaller.

A zoom lens is one of varying focal lengths which allows the photographer to get closer or further away from the subject, obviously within the restrictions of the overall focal range of the actual lens, without physically moving. This is advantageous because it allows the photographer to increase, or decrease the amount of frame the subject fills on the spot and without having to go for a wander. There is no doubt about it, zoom lenses are far more versatile than fixed focal length prime lenses. 

So, the question has to be asked “is a prime lens best or is a zoom lens best?” The zoom lens is far more versatile due to the fact of the range of focal lengths that are available. The zoom lens can be used to get in tight and fill the frame or it can be used for a broader shot. For example, when using a zoom lens to take an image of a bird the photographer can zoom right in on the head and achieve excellent feather detail and textures or the photographer can zoom out and capture the whole bird and some of its surroundings.

The range of focal lengths makes the zoom lens the ideal lens as a general every day lens or a walkabout lens. In addition, a zoom lens is the best lens for beginners as it makes shot composition that much easier. The problem with zoom lenses is that they are big, heavy and expensive. In addition, the more features you have on the zoom, such as professional grade optics and image stabilisation technology the more expensive they become. Unless you buy a top end zoom lens with a constant maximum aperture, optical quality is likely to be compromised so this needs to be borne in mind before buying the zoom lens. Not all zoom lenses are expensive and there are many cheap zoom lenses around. Whilst these are more than good enough for the photographer that takes the occasional picture whilst on holiday, or during family parties or during special occasions etc. cheap zooms are not good enough for those photographers that want the best optical quality.

The argument over whether the zoom lens or the fixed prime lens is better is an ongoing one and one that is highly unlikely to ever be settles. Both zoom lenses and fixed length prime lenses have their advantages and disadvantages. In the field, it is entirely down to the likes and dislikes of the individual photographer as well as the specific type of situation the photographer is in when trying to take the shot as well as the amount of gear the photographer wishes to carry a round. Does the photographer mind carrying around many fixed length prime lenses, which is going to be heavier, more difficult to keep an eye on when using the camera, a bit of a chore etc. etc or is this not acceptable? In the latter, the only viable option is a zoom lens. It really is a case of “you pays your money you takes your choice” and the decision is up to you.



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