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What you need to know before buying your first lens

Updated June 2021

A camera is nothing without a lens, and while the bundled ‘kit’ lenses sold with many interchangeable lens cameras (ILCs) are good enough to get started, they’re quite limiting. If you want to explore the full potential of your camera – and your own creativity – you should consider adding another lens or two to your collection. But with a bewildering variety of lenses out there, how do you know which ones are right for you?

In this guide we’ll lead you step-by-step through the process of understanding the different kinds of lenses available, and choosing the right one for your needs.

Lenses and sensors

Lenses themselves know nothing of the sensor mounted behind them, but different sized sensors change the visual impact of the lens (specifically the focal length and aperture) on the final image.

Among interchangeable lens cameras today there are three commonly-used sensor sizes: Four Thirds, APS-C and full-frame. The examples given in the rest of this article are lenses designed for full-frame bodies but we’ll also discuss what impact sensor size will have.

How are lenses named?

Looking at the lens pages on manufacturers’ websites can be a little intimidating for a budding photographer. Lens names often include long lists of letters and numbers, which certainly sound impressive but can also be thoroughly confusing. Luckily you can safely ignore most of them to start off with, and concentrate mainly on just a few factors:

  • Focal length – this defines how wide or zoomed-in a view the lens provides
  • Aperture – expressed as ‘F’ or ‘f/’ this describes how much light the lens can gather and its ability to blur the image background
  • Image Stabilization – some lenses include optical stabilization units to counteract the blurring effects of hand shake
  • Format – describes the sensor size the lens is designed to work with
  • Lens mount – determines whether the lens will physically fit your camera

We’ll look into each of these in more detail below.

Focal length

The first number used to describe a lens is its focal length; in combination with the camera’s sensor size, this defines the angle of view covered by the lens, with smaller ‘mm’ numbers indicating a wider angle or more ‘zoomed out’ view. Zoom lenses are named using two numbers which indicate the extremes of the range, for example 24-70mm for a typical kit zoom lens. Fixed focal length lenses which don’t zoom (also known as ‘prime‘ lenses) just have a single number (e.g. 50mm).

Here, we can see this lens’ key specifications expressed in terms of its focal length span (‘zoom range’) which is 18-35mm, and its minimum aperture range, which is F3.5 at 18mm, and F4.5 at 35mm.

The image below shows how the angle of view varies with focal length. In this instance it shows the effect of these lenses mounted on a full-frame camera. The same focal length lenses, mounted on a smaller, APS-C sensor would give a narrower, more cropped-in angle of view, and an even narrower coverage if mounted on a Micro Four Thirds format camera.

The effect is as is as though you’ve ‘zoomed’ the lens, but instead you’ve only magnified a smaller portion of its projected image. As a result, the focal lengths that are useful on one sensor format will differ from those that you’d use for the same purpose on another sensor.

Illustration showing the coverage given by a series of popular focal lengths. These are shown for a full-frame sensor; each would cover a smaller area if used with an APS-C or Four Thirds sensor.
Lens type
35mm ‘full-frame’
APS-C / DXFour Thirds
Ultra wide angle24mm and wider16mm and wider12mm and wider
Wide angle28mm18mm14mm
Standard (Normal)50mm30mm25mm
Telephoto80mm and longer55mm and longer42mm and longer

For the sake of convenient comparison, lenses are often referred to by their ‘35mm equivalent‘ focal length; for example a 18-55mm kit lens for APS-C may be described as a 28-90mm equivalent. This means simply that an 18-55mm lens on an APS-C format camera covers the same angle of view as a 28-90mm lens does on a full-frame camera.


The aperture specification of a lens describes how much light it is capable of gathering. Aperture simply means ‘hole’; in this context, the hole that lets light pass through the lens and onto your camera’s sensor.

Lens apertures can be expressed in several different ways, with F4, f/4, 1:4 all meaning the same thing. Confusingly, a smaller number means the lens has a larger maximum aperture – a bigger hole – and therefore can gather more light; an F2.8 lens collects twice as much light as an F4, for example.

‘Whole stop’ Aperture values

This table lists the common aperture values that are one ‘stop’ apart: each value lets in twice as much light as the one to its right.

A lens with a larger maximum aperture allows you to shoot in lower light, and (for example) take pictures indoors without using flash. Wide apertures also give decreased depth of field (i.e. how much of the picture in front of and behind the focus point appears sharp), which is an important aspect of creative photography.

Longer lenses give less depth of field for the same aperture, when focused at the same distance. And, because you need a shorter focal length to get the same image framing on an APS-C or Micro Four Thirds camera, you’d need a larger aperture if you want to achieve the shallow depth of field you’d get on a full-frame camera.

A large aperture such as F1.4 gives a shallow depth of field, blurring backgrounds and foregrounds to isolate a subject in a picture. The 24mm F1.4 used to take this picture also allows you to shoot indoors in low light without having to resort to flash.

It’s worth noting that lenses are usually described by their maximum aperture value. When you see an aperture range written on the side of a lens (e.g. F3.5-5.6), those are the maximum aperture values at the wide and long ends of its zoom range, respectively. You can usually reduce the size of the aperture if you need more of your image to be in focus.

Image stabilization

Image stabilization increases the amount of sharp images you get by correcting vibration caused (usually) by natural hand-shake when shooting without a tripod.

In-body stabilization (where the camera’s sensor moves to counteract accidental movement) is increasingly common, but many lenses offer their own stabilization mechanisms to compensate for shake. In-lens stabilization is especially effective when using long telephoto lenses, where in-body stabilization is generally not as effective. Many cameras can use in-lens stabilization in conjunction with their in-body systems, to provide a greater degree of correction.

Image stabilization systems reduce the blur caused by camera shake, allowing sharp pictures to be taken even in low light, at long focal lengths or at high magnifications.

If you own a camera that doesn’t have stabilization built into the body, you’ll probably want to consider buying stabilized lenses, especially when it comes to telephotos.

The various lens manufacturers all call lens-based optical image stabilization by different names, with corresponding initials in the lens names, so here’s what you need to look out for when buying:

  • Canon – Image Stabilization (IS)
  • Fujifilm and PanasonicOptical Image Stabilization (OIS)
  • Nikon – Vibration Reduction (VR)
  • Sony – Optical Steady Shot (OSS)
  • Sigma – Optical Stabilization (OS)
  • Tamron – Vibration Control (VC)

Format coverage

Having said that sensor format has a significant impact on the way lenses behave, it’s also worth considering that some lenses only work on certain sensor formats. In several instances, camera makers use the same mount for their APS-C and full-frame cameras. In most of these situations, full-frame lenses will work on the smaller APS-C models, but APS-C lenses end up restricting full-frame cameras to a cropped APS-C mode.

Some photographers start with an APS-C camera and then buy full-frame compatible lenses for it, to lower the amount of money they have to spend if they later buy a full-frame camera that uses the same mount. In general, we’d advise buying lenses that suit your needs now, rather than ones that may better suit a camera you don’t yet own.

Lens mounts

Each camera maker uses its own proprietary lens mount, meaning that lenses can’t be swapped across brands; a Canon lens won’t fit on a Nikon body, for example, and you’ll cause damage to both lens and camera if you try. The two exceptions are Micro Four Thirds, which was developed jointly by Panasonic and Olympus, and L-mount, a full-frame collaboration between Leica, Panasonic and Sigma.

Most companies are now focusing their efforts on their Mirrorless camera mounts, so this is where the newest and most advanced lenses are emerging. Many DSLR-mount lenses can be adapted to work on the mirrorless cameras made by the same brand (older designs are less likely to offer a full range of functions) but lenses for mirrorless cameras cannot be used on DSLRs.

MountMount typeSensor formatsNotes

• Full-frame



Canon EF-S lenses cannot be mounted on full-frame DSLRs but other brands’ EF-mount APS-C lenses can.


EF and EF-S lenses can be adapted to work on EF-M cameras

• Full-frame

Most EF-mount lenses work well on RF mount via an EF/RF adapter.
Four Thirds
• Olympus
• Panasonic
Micro Four ThirdsMirrorless• Four Thirds
FujifilmXMirrorless• APS-C
L-Mount Alliance
• Leica
• Panasonic
• Sigma

• Full-frame
• APS-C (TL)

Only Leica has made TL-mount (APS-C) cameras and lenses.

• Full-frame
• APS-C (DX)

F-mount was modernized over many decades but only relatively modern ‘AF-S’ designs offer AF when adapted onto Z-mount cameras

• Full-frame
• APS-C (DX)


• Full-frame (FA)
• APS-C (DA)

As with Nikon, there are variants of the K mount, but most lenses work with the latest DSLRs

• Full-frame (FE)
• APS-C (E)

Other lens makers use ‘E’ for both APS-C and full-frame lenses, so it’s worth checking which format they cover

A number of third party manufacturers, including Tamron, Tokina and Sigma make lenses for other makers’ lens mounts, with the older DSLR mounts benefiting from the widest support. Sony allows some third-parties to make lenses for its mirrorless E-mount system but Nikon and Canon have, so far, been protective of their new Z and RF mounts, meaning there are fewer third-party options available.

Zoom vs. Prime

Zoom lenses have become almost ubiquitous over the past few years, and at first sight buying a lens which is restricted to a single angle of view might seem pointless. But prime lenses still have some very real advantages; compared to zooms they tend to be smaller and lighter, have faster maximum apertures, and give sharper, cleaner images. These factors make them extremely useful for specific purposes, for example low light shooting or blurred-background portraiture where a large maximum aperture is advantageous.

Almost counterintuitively, the restrictive nature of using a single focal length can encourage creativity by forcing you to visualize your composition before you shoot. Shooting with primes forces you to think more about what you want to include and exclude from your photo and also makes you consider where you’re standing, and the impact this has on perspective in your image. For instance, a long focal length, shot from a distance can compress your subject and the background, whereas a wide-angle lens placed near your subject will exaggerate the distance between it and the surroundings.

Fixed focal length ‘prime’ lenses are often much smaller and lighter than zooms covering the same angle of view. This is Nikon’s Z-mount 35mm F1.8 lens alongside its standard 24-70mm F2.8 zoom – the size advantage is obvious.

Some popular lens types

Standard zoom

A standard zoom is a general-purpose lens that covers a range of focal lengths from wide-angle to moderate telephoto. The most obvious example is the kit lens that came with your camera (generally something like an 18-50mm for APS-C or a 24-70mm for full-frame). It offers versatility but can become limiting when you find yourself wanting to get more creative. The kit lens can be upgraded to an optic with more range or a faster F2.8 maximum aperture, with better optical performance, like the Canon RF 24-70mm shown F2.8 below.

Most manufacturers offer general-purpose upgrades to their kit lenses with expanded zoom ranges suitable for a wide range of subjects, such as this Canon RF 24-70mm F2.8.

Telephoto zoom

Often the second lens that photographers buy, a telephoto zoom effectively allows you to ‘get closer’ to your subject by enlarging it within the frame. It’s therefore useful for photographing such things as sports, wildlife, distant nature scenes, or children running around playing. By narrowing your field of view, a long lens can have the effect of compressing your subject and background, often making it appear as though the background is magnified and closer to your subject.

Telephoto zooms such as this Nikon Z 70-200mm F2.8 S allow you to zoom in on your subjects and compress them against the background.


Superzooms are all-in-one lenses which cover a full range of focal lengths from a moderate wide-angle to long telephoto. In one package they combine the range of the kit zoom that came with the camera, plus that of a telephoto zoom, and therefore make perfect general purpose travel lenses. The technical image quality is often not quite as good as two separate lenses, and the maximum aperture tends to be small (a higher F-number), meaning worse low light performance and less ability to achieve shallow depth of field. However, for many users this is more than made up for by their convenience.

Superzoom lenses such as the Tamron 28-200mm F2.8-5.6 Di III RXD encompass a wide range focal lengths from wide-angle to telephoto, in a relatively compact single lens.

Wide-angle zoom

A wide-angle zoom extends the angle of view out beyond that captured with the standard zoom, allowing you to capture broad sweeping vistas or architectural wonders. It’s therefore a popular choice for landscapes, cityscapes, architecture, interior shots, and night- and astro-photography.

Wide zooms such as the Sony 16-35mm F2.8 pictured here let you fit more in the frame.

Macro lens

‘Macro’ is used to describe a lens with extreme close-focusing ability, which allows you to take photographs of small objects such as insects or flowers. Some zoom lenses use ‘macro’ in their name to indicate closer-than-usual focusing ability, but true macro lenses tend to have fixed focal lengths. In general, the longer the focal length, the further away you can be from your subject. (Nikon calls these lenses ‘Micro’ or ‘MC’ lenses instead, which is technically more accurate.)

Macro lenses like the Sigma 105mm F2.8 DG DN Macro allow you to shoot closeups in fine detail.

Fast prime lens

Fast prime lenses come in all focal lengths, from wide angle to ultra-telephoto, but what they share in common is the ability to capture a lot of light, blur backgrounds and offer high optical quality.

We’ve traditionally found 35mm (or the equivalent 23mm or 17mm on APS-C or Four Third sensors) to be a pretty good do-everything focal length, in terms of not being too wide or too zoomed-in. An F1.8 maximum aperture can give shallow depth of field and lets you work in low light without the need for flash, while remaining compact and lightweight. Wider-angle and longer focal length primes are also available, as are lenses with even faster maximum apertures (F1.4 and brighter) that typically offer higher quality optics, let you work in lower light and give even shallower depth-of-field to help isolate your subject.

A ‘fast’ prime, such as this Canon 35mm F1.8, can let you shoot in low light without flash, while isolating your subject against a blurred background. They are also typically smaller than zoom lenses.

Other lens features

There are a few other aspects of build and operation which you may wish to consider when buying a lens:


Autofocus performance can vary significantly between lenses, and autofocus performance can make a huge difference between capturing the perfect moment at a sports event or social occasion and having a frustrating photographic experience.

Mirrorless camera systems are still relatively new, and there’s a subtle interplay of optical design and focus motor that effects performance. For instance the ring-type ultrasonic motors that were great for focusing on DSLRs aren’t as well suited to focusing on mirrorless cameras, particularly for the smooth, subtle movements required for video autofocus. As such, it’s difficult to make generalizations, so it’s worth checking reviews of the lens you’re planning to buy.

Electronic manual focus (‘focus by wire’)

Many modern lenses have no physical connection between the focus ring and the focusing lens elements, as was the case in older SLR and DSLR lenses. Many cameras use this to provide speed-sensitive manual focus, where a quick turn of the focus ring results in a bigger focus jump than a slow movement. This lets you jump quickly to the part of the focus range you want, but can be awkward if you’re trying to manual focus while shooting video.

To get round this, some cameras offer a ‘linear’ focus response mode, where the focus always moves by the same amount in response to how much you turn the focus ring: letting you practice and anticipate the amount by which you need to turn the ring.

Manual focus lenses

Although modern autofocus is excellent, there is still a huge number of manual focus lenses on the market. These include designs optimized for shooting video and traditional, high-quality designs, through to unusual, specialist lenses that would be near-impossible to make autofocus along with the creations of small companies without the experience (or access to lens mount protocols) to manufacture AF lenses.

Ultra-wide angle lenses, tilt-shift lenses and some very expensive lenses designed to be mechanically simple but optically excellent are out there, and are worth considering.

Build quality and weather sealing

Premium lenses often include weather sealing. This can extend from an o-ring around the mount through to a series of seals at every joint, as with this Panasonic lens.

As a general rule, the more expensive a lens is, the better built it is likely to be. The kit lenses that come with cameras tend to rather lightweight and plastic in construction. If you spend a bit more, you can get something more durable. Some lenses incorporate environmental seals against dust and water; in general this tends to be towards the top end of the price spectrum, but Pentax and Olympus in particular offer a decent range of mid-priced sealed lenses.

System addict…

One last word. When choosing a camera system to invest in, it’s important to appreciate that the lens has just as great an impact on the image quality as the camera. Lenses tend to last longer than cameras too, becoming obsolete less quickly than bodies, so it can be worth spending a little bit extra to get the quality or flexibility you really want. But, while DSLR systems are much more extensive, most new lens development is focused on Mirrorless cameras, so these may prove more future-proof.

Bear in mind that most mirrorless lens systems are still only a few years old, so they may be missing the type of lens you want, for now. That said, the system with most options isn’t inherently any better than a smaller system that includes all the lenses you need.

Even if you don’t have a very specific application that needs specialized lenses (or other accessories) in mind, it’s worth doing some research before committing to one system or another. Oh, and once bitten by the lens buying bug, many enthusiasts find it hard to stop; you have been warned…


Angle of view – Describe the view offered by a lens, measured as the angle between the furthest extremes of the lens’s coverage. If this is confusing, imagine the view in front of you as a semicircle of 180 degrees: a ‘wide-angle’ lens can see a bigger segment of the semicircle than a ‘long’ (telephoto) one.

Depth of field – This describes how much of the scene in front and behind the point of focus appears acceptably sharp. An image with shallow depth of field leaves the background (and foreground) appearing blurry and out-of-focus. An image with deep depth of field contains a greater amount (depth) of sharp detail.

Fast / slow lens – An informal way of describing a lens’ aperture in terms of its relation to exposure time. ‘Fast’ lenses have large maximum apertures (low F-numbers), which allow the use of shorter, ‘faster’ shutter speeds. ‘Slow’ lenses have smaller maximum apertures, and typically require longer, ‘slower’ shutter speeds.

Focal length – Expressed in millimeters, focal length describes the angle of view of a lens. Telephoto lenses have a long focal length, and wide-angle lenses have a short focal length. The longer the focal length, the narrower the angle of view and the more zoomed-in it appears.

Long / wide lens – A way of describing the field of view offered by a lens. Long lenses are more zoomed-in, while wide lenses are zoomed-out and capture a wider angle of view.

Micro Four Thirds – A mirrorless system founded by Panasonic and Olympus, based around a 17.3 x 13mm sensor (224 sqmm) format known as Four Thirds. The system allows some very compact camera/lens packages, particularly for very long telephoto lenses. This system includes some high-end video cameras.

APS-C – A common sensor format used by interchangeable lens camera manufacturers. APS-C format sensors measure around 24 x 15mm (~360 sqmm), and this format offers a balance of image quality, size and price in between Four Thirds and ‘full-frame.’

Full-frame – A sensor format the same size as a frame of 35mm film – the dominant film format of the 20th and early 21st Centuries. Measures 36 x 24mm (864 sqmm), giving a significant image quality benefit compared to smaller formats, but resulting in larger, more expensive camera/lens combinations. Despite the name, sensor larger formats do exist, in sizes known collectively as ‘medium format’.

Prime lens – A lens with a fixed focal length, which cannot zoom in or out. A technical term not to be confused with Amazon Prime.

Zoom lens – A lens whose field of view (described in terms of focal length) can be adjusted, allowing you to zoom-in or out on a subject, to achieve a different composition without changing your position.

35mm / full-frame equivalent – A way of understanding the characteristics of a lens when used on a non-full-frame camera by relating it to the 35mm film format that’s familiar to many photographers. Most commonly used in reference to focal length: e.g a 28mm lens on an APS-C camera is equivalent to a 42mm lens on a full-frame camera.