differences between prime and zoom lenses

Prime vs. zoom lenses − Help with choosing a lens

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Trying to choose between a zoom and a prime lens can be challenging, mainly because they probably shouldn’t be compared in the first place. Basically they offer different outcomes. A prime is almost a lens specialized for a particular task, whereas a zoom can be more of a “jack-of-all-trades”. There are also different types of each of these lenses. There are expensive fast primes, and less-expensive primes with a slower maximum aperture. There are also native primes from the camera manufacturer, and third-party primes. The same criteria can be applied to zoom lenses. Table 1 summarizes some of the key differences between prime and zoom lenses.

characteristicprimezoom
price+ simple build, less expensive− complex build, more expensive
aperture+ brighter, wider aperture (faster)
e.g. f/1.2 to f/2		− darker, narrower aperture (slower)
sharpness+ sharper images, fewer optical deficiencies− less sharpness, some distortion
versatility− less versatile+ more versatile
size and weight+ lighter and more compact
− have to carry more lenses		− bulkier and heavier
+ need to carry fewer lenses
Table 1: Key differences between prime and zoom

A zoom provides a level of flexibility that a prime does not, but this comes with some trade-offs. The first thing a zoom lens typically gives up is speed, i.e. how wide the aperture opens up. Prime lenses on the other hand are fast, and some are super-fast. Note that prime lenses are nearly always smaller and lighter than zooms. Many things influence the size and weight of a lens including whether it is a pro-grade lens (often contain more glass), or whether it has a large maximum aperture (again requiring a bigger lens with more glass). Every lens has its pros and cons.

Fig.1: A very basic schema for choosing a prime or zoom lens

Despite the fact that prime lenses are often lauded for their specific nature, i.e. suited to one particular task, zoom lenses can also be categorized in this manner. For example someone might choose a 17-28mm full-frame lens for landscapes, providing some scope. In addition, although a good zoom lens may be more expensive than a prime, more prime lenses may be needed to equal the range of coverage, thereby leading to more cost. There are also some lenses that don’t work very well as a zoom, e.g. fish-eye lenses.

When selecting a prime lens it is often the case of deciding on an application, and then which lens meets all the criteria. For example, a trip to Iceland may warrant a wide-angle lens that is weatherproof (because the weather can change every 5 minutes in Iceland) − in this case something like a 24mm ultra-wide would be optimal. Alternatively, some photographers might opt for even a wider lens, e.g. 16/18mm due to the ‘largeness’ of the landscape. Choosing a zoom lens on the other hand can be a little more challenging. This is because there are often a variety of options. For example, choosing a 50mm prime means you get a 50mm lens, with perhaps the only variability being the speed (maximum aperture) of the lens. But there may be more than one option for choosing a particular zoom lens. Figure 2 shows a flowchart which considers some of the main factors to consider when choosing a zoom lens.

Fig.2: Factors to consider when choosing a zoom lens

Figure 3 shows an example of choosing a wide zoom lens for a Fuji-X camera (APS-C), using the above factors. There isn’t that much difference between the lenses with respect to AOV (angle-of-view), but as each factor is considered, more lenses are filtered out. At the end only three of the five lenses satisfy the criteria considered, and then it comes down to price. If we were choosing this for the trip to Iceland then we might want the greatest flexibility in focal lengths, for example the Fujifilm 10-24mm (FF equivalent 15-36mm). If maximum aperture is an issue, then either the Tamron or Sigma are fine alternatives.

Fig.3: An example of choosing a Fuji (wide) zoom lens for landscape

There are some situations where one lens is just enough. Mountain enthusiast Jakub Cejpek talks about using the Fujifilm XF10-24mm/F4 on a mountain trek. He chose mirrorless for its ‘lightweight style’, and the 10-24mm lens for its versatility, knowing that changing lenses in impossible, ‘time is rare, and weather conditions are tough’.

Prime vs. zoom lenses − Is one better than the other?

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One of the biggest dilemmas for novice photographers when choosing a digital lens is whether you buy a prime or a zoom? This is an age old debate, probably dating back to the 1970s when zoom lenses started to make real inroads into the SLR lens market. Back then zoom lenses were at a major disadvantage from a quality perspective, but over time they have improved in quality, and proliferated in quantity. Here we look at the major differences between the two.

Fig.1: A comparison of a modern prime (50mm normal) versus a modern zoom lens (wide-to-short telephoto, 17-70mm), both full-frame.

Zoom lenses

A zoom lens is a lens designed with a variable focal length. This allows the lens to be modified to any focal length between the specified range, meaning the angle-of-view (AOV) of the lens will change with the focal length. For example 16-80mm means the lens is widest at 16mm, and at full zoom at 80mm. There are zoom lenses that are narrow in focus, e.g. wide-angle zooms where the zoom range covers wide-angle focal lengths, and there are others that are more broadly scoped, e.g. 17-300mm, covering wide-angle all the way through medium length telephoto. Some zooms have a fixed aperture, i.e. one maximum aperture, others have a variable aperture which changes with the focal length selected, e.g. a 28-60mm f/4-5.6 means that 28mm the aperture is f/4, while at 60mm the aperture is f/5.6.

Many cameras come standard with a kit lens which is typically a zoom. For example Fuji-X (APS-C) often pairs a 15-45mm zoom (f/3.5-5.6), with covers a horizontal AOV of 77.32° to 29.8° − wide angle to low-telephoto to cover from landscapes to portrait shots. Other Fuji cameras are paired with 16-80mm or even 18-120mm. Note that the downside to kit lens, is that they are typically of lower quality.

Pros:

  • Versatility − Zoom lenses offer a lot of flexibility, allowing the focal length to be changed on-the-fly (so there is no need to swap-out lenses). This makes them ideal for situations where there is a need to quickly adjust the framing.
  • Convenience − There is no need to carry multiple lenses to cover different focal lengths.
  • Discretion − A scene can be captured without having to get too close. Using one lens also means it may not be necessary to carry a camera bag.
  • Portability − A single zoom lens can replace 2-3 prime lenses. This means less weight to tote around, and less lens swapping, so although the zoom may weigh more, it may be less than the sum of primes.

Cons:

  • Optical quality − Zooms can sometimes be less sharp than primes because of their complex, variable nature. However the gap between the quality of zooms versus primes is narrowing. An expensive zoom is likely to have better optical quality than a cheap one.
  • Aperture − Professional zooms have a maximum aperture of around f/2.8, or even f/4, making them less than optimal for low-light situations, i.e. slow.
  • Price − Zoom lenses can be expensive, because the zoom mechanism and lens configuration can be complex. Kit zooms are cheap, the Fuji-X 15-45mm is around C$325. The Fuji-X 16-80mm is C$880. Wide zooms can be even more expensive with the Fuji 10-24mm going for C$1050.
  • Weight − Generally quality zooms can be heavier than primes because the lens body is physically larger, and there are more complex mechanisms inside, e.g. auto-focusing motors.
  • Lens selection − Some platforms do not offer that many zoom lenses. For example there are a lot of third-party lenses in the Fuji-X environment, however most are prime lenses (probably due to the lower cost). Apart from Fuji native zooms, the only real competitors are Sigma and Tamron.
three prime lens compared to an equivalent zoom lens
Fig.2: A comparison of a 16-55mm zoom lens with three ‘equivalent’ prime lenses to covert the same range of focal lengths (note that the closest to a 55mm prime is a 56mm f/1.2 which puts it outside the bounds of comparison from the perspective of aperture).

Prime lenses

A prime lens is a lens with a fixed focal length, meaning it cannot change. It has an AOV that is set, so making an object fill more of the frame requires getting closer to the subject. For example a 16mm Fuji-X prime offers a horizontal AOV of 73.74°, no more, no less. So to enlarge a subject and make it fill more of the frame, the camera has to be moved physically closer to it. To make a subject fit a frame, the camera must be moved away. In terms of prime lenses, a wide angle might be 28mm, a normal lens 50mm, and a portrait lens 85mm (full frame). In comparison a 28-85mm zoom lens offers all these focal lengths (and many in between) in a single lens. Prime lenses are typically fast, with maximum apertures of f/1.8, f/1.4 or even f/1.2 (or faster).

Pros:

  • Optical quality − Prime lenses are focused on one focal length, and as such often have better optics. This includes having a better depth of field, sharpness, and rendered bokeh. Better optics = better image.
  • Aperture − Prime lenses are faster than zoom lenses, i.e. they have larger maximum apertures than zooms. They can have apertures as wide as f/0.95, but typically they are between f/1.2 and f/2.8. This makes them better in low-light situations, and helps them produce a shallower depth-of-field. This often negates the need for a flash or high ISOs that can introduce noise.
  • Focusing speed − Auto-focusing generally works a little faster on prime lenses.
  • Price − Prime lenses have fewer moving parts and as such can be less expensive. The caveat here are specialty lenses, superfast lenses e.g. f/1.2, and super-telephoto lenses. Prime lenses have the same range of cheap “kit” to expensive high-end lenses, but often it is possible to purchase a good prime for a reasonable cost. Note that superfast lenses can be significantly more expensive than their f/1.8 counterparts.
  • Compactness/Weight − Many normal prime lenses are generally lighter and more compact than zoom lenses.
  • Bokeh − Wide apertures provide a shallow depth of field, which makes primes ideal for taking portraits and artistic shots containing the coveted background blur known as bokeh.

Cons:

  • Limited versatility − Prime lenses only have one focal length, so it might be necessary to carry more than one lens to cover a gamut of scenarios. Adjusting a composition will require moving towards or away from the subject.
  • Inconvenience − With prime lenses it may be necessary to carry multiple lenses to cover different focal lengths. This impacts how much needs to be carried in the field.
  • Discretion − Carrying more than one lens might require changing lenses on-the-fly, because different lenses may be used for different scenes. A camera bag might be a requirement.
  • Portability − While a zoom lenses can replace a number of prime lenses, working only with primes may require carrying 2-3 lenses with different focal lengths. This means more weight to tote around, and more lens swapping.
  • Weight − There are circumstances where primes can be heavy, e.g. super-fast lenses often require more glass, which makes them heavier than other primes, and telephoto lenses can be larger and heavier than telephoto zoom lenses.

Choosing between a prime and a zoom lens really depends on photographic priorities, i.e. what is needed in a particular situation. Zoom lenses can be hard to use well for the inexperienced photographer − e.g. they often stay in one position, and zoom to capture everything, versus using a prime lens where you are forced to move in order to gain photographic perspective. Every optical design has its strengths and weaknesses, but as a prime lens is optimized for a single focal length in many cases it has a greater capacity for fewer weaknesses and more strengths. This may include characteristics such as: image quality (contrast, sharpness, distortion, flare control), colour aberrations, lens speed, size and weight, focusing ability, focus shift, etc.