Difference between a zoom lens compared to a prime fixed focal length lens

Experienced photographers who have been around for a while, often prefer prime (fixed focal length) SLR camera lenses over zoom models. Photography magazines always suggest the sharpness of fixed focal length lenses far outweigh the flexibility of zoom lenses.

Before looking at the advantages and disadvantages of both we first need to know ‘what is a zoom lens or prime lens’.

What is a zoom lens?

A zoom lens is one that has a retractable zoom ring, making it easier to get in as much or as little of the scenery as you want, without the need to physically move yourself. If the lens name has a hyphen between two mm extreme’s, then it is a zoom lens. For example, a Canon EF-S 17-85mm f/4-5.6 IS USM is a zoom lens. The focal length can be set from 17mm to 85mm.

What is a prime fixed focal length lens?

A prime (fixed focal length) lens is set to one mm focal length. In other words, the focal length cannot be adjusted. If you want to get more or less of the scenery or object in the photograph, then you need to physically move yourself in or out. For example, a Nikon AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED lens is a prime lens because it has a fixed focal length of 105mm.

Other differences between DSLR zoom and prime camera lens

  • Prime lenses take sharper photographs than their zoom counterparts, because from a design point of view they have fewer compromises. It makes sense that if a lens is designed to zoom from between 17mm and 85mm, then it’s going to be harder to make than one that has a fixed 105mm focal length. A good example of compromises found in zoom lenses, can be seen in the distortion problem many of them have.
  • While it’s true a zoom lens may not be as sharp as a prime lens, they are however cheaper. Therefore the tradeoff for sharpness, is price cutting costs.
  • As explained earlier, a prime lens requires the photographer to physically move themselves closer or further away from the subject depending on the situation. Many amateurs find this annoying, therefore opting for zoom lenses.

Should you buy a zoom lens or a prime fixed focal length lens for your digital SLR camera?

Personally, I think both have their place when it comes to good photography. If sharpness is the main concern and you are photographing a subject where you can easily position yourself physically, then a fixed focal length lens (prime) is the way to go.

However, there are times when physically moving yourself closer or further away from the subject isn’t a possibility. For example, if you were on a whale watching cruise, the restrictions of a prime lens would be useless. For times like this, a zoom lens would be more beneficial.