Which lens? Choose the best lens for your DSLR
10th Oct 2011 | 15:32
DSLR lenses explained: from fish-eye to telephoto
Key camera lens specifications explained
Thinking of buying a lens for your DSLR or compact system camera (CSC)? Deciphering the different key specifications and working out which lens to buy can be difficult.
Don't know your apertures from your focal lengths? Your APS-C from your Micro Four Thirds? Your telephotos from your superzooms? Then TechRadar's camera guide to buying the best lens for you can help.
Read our Best zoom lens upgrade: 8 tested article
Read our Best macro lens: 8 tested article
Read our Best travel lenses: 8 tested article
Read our Best wide-angle lenses: 8 tested article
We'll start by explaining the key features of DSLR and CSC camera lenses, and then we'll take an in-depth look at the different lens types available, from prime lenses to fisheyes.
Your lens markings explained
If a camera's sensor is the brain, then its lens is akin to the eyes - and both elements are essential to complete the modern picture-taking package.
While there are shed loads of compact cameras that come as all-in-one sealed units, the interchangeable system camera market - ie DSLR and compact system cameras (CSC) - allow you to chop and change between different lenses.
But why would you choose to do this? Like our own eyes a camera's lens sees the world with a particular field of view, depending on its focal length. Focal length is described in millimeters.
But unlike our eyes, lenses can be made with completely different perspectives on the world. The smaller the focal length value (for example a 10mm wide-angle), the wider the angle of a frame will be. A wide-angle lens has a field of view that takes in far more than our eyes ever could in one sitting.
In contrast, a higher focal length value (such as a 300mm telephoto) 'trims' or 'zooms in' on the field of view and gives the impression of far away subjects appearing magnified.
While we're familiar with our own field of vision, other animals have different takes on the world. The common rabbit, for example, has a wide angle of view and can see almost all around, whereas many birds of prey have narrower vision like a telephoto lens in order to locate their far-off prey.
Sensor size and aperture explained
Different camera bodies have different sensor sizes, with full frame, APS-C and Micro Four Thirds being the three most common examples. Smaller sensors crop into the equivalent full frame image, which is why you may have heard the term "crop factor".
In order to understand this, imagine a sheet of A4 paper (this represents our full frame sensor) with an image projected to its exact proportions via a 50mm lens. If you were to lay a sheet of A5 paper over the top of this (let's call this our APS-C sensor) then the new frame's edges won't fit the image's outermost edges in, thus a crop has occurred. It looks like the image has been taken formed by a longer focal length lens.
In general, APS-C format cameras have a multiplication factor of around 1.5x, so 50mm multiplied by 1.5x equals a 75mm equivalent.
A Micro Four Thirds sensor is even smaller than APS-C size and so has a 2x crop factor. As a result, the same 50mm multiplies by 2x and produces images like a 100mm lens - hence it has 100mm equivalence.
The word "equivalence" is important, because focal length is a constant measurement that doesn't change, whatever sensor format you're using. Try not to get too bogged down in the maths, but visualising what's happening can help to make this often confusing matter more manageable.
Another important factor to consider about a lens is its maximum aperture. The aperture - also described as the f-number or f-stop - is the size of the lens opening through which light passes.
Lenses that have a large maximum aperture such as f/1.8, f/2.0 or f/2.8 are generally more highly prized (and expensive) than those with maximum apertures of f/4 and f/5.6 because they allow more light in so that faster shutter speeds can be used. Hence why they're often called fast lenses.
Fast lenses are useful in low light and when fast shutter speeds are required to freeze movement - for example in sports photography.
Another important factor with larger aperture lenses is that they enable greater control over depth of field.
Depth of field is the sharp zone that extends in front and behind the subject (or focal point) before it gradually becomes blurred.
Physics dictates that the larger the aperture (for example f/1.4), the shallower the depth of field or sharp zone. A smaller opening (for example f/22) produces much wider depth of field and avoids background blur.
The longer the focal length of the lens, and the closer the subject, the more restricted the depth of field is at any given aperture. Hence smaller apertures are required to get more of the image sharp when long lenses are used or the subject is closer to the camera.
Many zoom lenses have a variable maximum aperture, for example f/3.5-5.6. The first number refers to the maximum aperture at the widest angle setting; the second number to the maximum at the longest zoom setting.
Zoom lenses with a constant maximum aperture tend to be more expensive, because the exposure doesn't change as you zoom in or out.
Now take a breath, mull over those technical thoughts and read on for our full lens type guide, with example products for each type of lens from Canon, Nikon and other trusted camera brands.
A prime lens is a fixed focal length camera lens.
While a prime lens can have any focal length, it's the more traditional focal lengths from around 24mm up to 105mm that prove the most popular in today's market. This is a reflection of lenses found on older, classic cameras. The restriction of having only a single frame onto the world to work with is often deemed to provide its own creative process.
Modern day prime lenses typically have wide maximum aperture settings - some as bright as f/1.2 if you've got the cash - that give shallow depth of field control often far out of reach of zoom lenses (or, to be more accurate, affordable zoom lenses).
The quality of construction is also tip-top and, because they don't change focal length, they often produce super sharp images that are far better quality than a zoom lens equivalent.
The compact size is also an attractive reason to work with a prime lens, and the recent surge in compact system cameras (CSC) is testament to how small a camera kit can be crunched down to with a pancake (very thin) lens attached to the front.
Current favourites include the Canon EF 50mm f/1.4, available for a bargain £300, although prices can skyrocket for the best of the best: take a look at Sony's 24mm f/2 Distagon T* ZA SSM lens and you'll need closer to the £1,000 mark.
Typical Prime lens examples
Nikon 85mm f/1.8 D AF - £305
Canon EF 50mm f/1.4 USM - £299
Sony A-mount 24mm f/2 Distagon T* ZA SSM - £990
Olympus Zuiko Digital 35mm f/3.5 - £210
Pentax 77mm f/1.8 FA - £769
Sigma 20mm f/1.8 EX DG - £534
Sony E-mount (NEX) 50mm f/1.8 OSS - £269
Olympus Zuiko Digital 45mm f/1.8 Micro Four Thirds - £249
Samsung NX 30mm f/2.0 - £190
Wide-angle and fisheye lenses
Wide-angle and fish-eye lenses
As their name suggests, wide-angle lenses produce an image that's broader than your eye can see. Ranging from effective focal lengths of around 14mm to approximately 50mm (this will differ depending on sensor size) a wide-angle lens is useful for squeezing more into a single frame.
However, perspective distortion - based on the subject distance and wider angle of view of the lens - can contort normal-looking subjects into more abstract forms.
For example, shoot a cube close-up and the nearside edges may appear longer than its others, even though this isn't the case. Hence wide-angle lenses are often best avoided for portraits - it'll distort the subject's face, magnifying the nose and central area of the frame out of proportion.
Wide lenses also tend to magnify the perceived distance from a subject and its background. Shoot a subject close up with a 14mm lens and a second subject behind will appear distant; frame up the same subject with a 50mm prime lens and the two subjects will appear to be closer together.
Different wide lenses also suffer from varying degrees of barrel distortion (that 'flex' in horizontal/vertical lines) that is often more severe the wider the angle of the lens is.
Go extra-wide and you're into different territory: Fisheye lenses are typically very wide-angle and come in two varieties - diagonal and circular.
Diagonal (sometimes called full-frame) fisheye lenses shoot images with heavily distorted characteristics but that still fit the image frame.
By contrast a circular fisheye, also known as a whole-sky lens, shoots a hemispherical image (like half a globe) where the circular outline of the shot can be seen within the frame.
At present Sigma's 4.5mm f/2.8 circular fisheye is the widest, offering a 180-degree angle of view in all directions.
Typical wide-angle lens examples
Nikon 14mm f/2.8 D AF ED - £1,214
Sony A-mount 20mm f/2.8 - £500
Olympus Zuiko Digital 8mm f/3.5 Fisheye Four Thirds - £715
Sigma 15mm f/2.8 EX DG Fisheye - £489
Pentax 14mm f/2.8 SMC DA ED IF - £537
Canon EF 20mm f/2.8 USM - £404
Olympus 12mm f/2.0 ED Zuiko Digital Micro Four Thirds - £650
A standard lens is designed to produce an image circle to closely cover the designated camera's sensor. It will also keep subjects in suitable perspective and proportion with little to no distortion.
The focal length of a standard lens is based on the diagonal measurement of the camera's sensor that the lens is paired with. This means that (to the nearest mm) Micro Four Thirds standard is 23mm, APS-C 28mm (this will vary based on different Canon and Sony sensor sizes) and Full Frame 43mm.
A common misconception is that 50mm equates to a standard lens, even though this is slightly longer, and cropped in to the image, by comparison. However, 50mm (or equivalent) optics have a similar field of view to the human eye.
Back when Pentax was producing 35mm (Full Frame) film cameras, it launched a 43mm lens that was the ideal standard focal length. On its current APS-C-sized sensor DSLR range this produces images similar to a 65mm equivalent, and it's a good portrait lens.
While standard lenses produce natural-looking shots reflective of life, hence being a common choice for street photography, many users will find them a little too wide-angle for all scenarios.
Sigma produces a 28mm f/1.8 lens for £350 that's the perfect pairing with an APS-C DSLR of any make. However, a lot of the other manufacturers don't quite offer the exact standard focal length, hence why we picked some slightly longer lenses in our listings below.
Typical standard lens examples
Canon EF 28mm f/1.8 USM - £389
Sony DT 35mm f/1.8 SAM - £158
Pentax 31mm f/1.8 FA AL - £1,049
Olympus Zuiko Digital 25mm f/2.8 Four Thirds - £215
Pentax 35mm f/2.4 SMC DA AL - £134
Sigma 28mm f/1.8 EX DC HSM - £350
Nikon 35mm f/1.8 G AF-S DX - £164
Samsung 20mm f/2.8 iFn - £235
Panasonic 20mm f/1.7 Lumix G Micro Four Thirds
A telephoto lens enables you to get in close on the action, and you'll often see dozens of these large-sized lenses in the professional photographer pit at football matches and other sporting events.
Focal lengths range from around 100mm through to a typical 400mm, although 500mm, 600mm and even longer lengths are also available (you'll be looking at spending several thousands for the pleasure).
If a single element was used to create a 500mm lens, then the front glass would need to be 500mm from the sensor plane.
By using multiple lens elements it's possible to redirect the light path and produce smaller-sized lenses with the same equivalent focal length, and this is what constitutes the term "telephoto".
Prime telephoto lenses are less expensive than their telezoom counterparts, and the optical quality is designed to extract the very best sharpness and image quality at a fixed focal length.
Wide apertures are also common, with f/2.8 and f/4 examples such as the Nikon 400mm f/2.8 and Canon EF 300mm f/4 representative of what's available.
As handshake is amplified at longer focal lengths, many current lenses use optical image stabilisation systems that move the internal lens elements by microscopic amounts to counter for this movement. It results not only in steadier framing, but a sharper final image too.
On the downside, these lenses are big, heavy and expensive. Outside of their specific use, telephoto lenses are not good for close focusing because they often have a minimum focus distance of some metres.
Typical telephoto lenses
Nikon Nikkor 400mm f/2.8 ED VR AF-S - £6,647
Olympus Zuiko Digital 300mm f/2.8 ED Four Thirds - £6,024
Sigma 500mm f/4.5 EX DG HSM - £3,774
Canon EF 300mm f/4 L IS USM - £1,144
Sony A-mount 300mm f/2.8G - £4,953
Pentax 300mm f/4 SMC DA* ED IF SDM - £915
Kit lenses and standard zoom lenses
A zoom lens has a variable focal length, for example 18-55mm, meaning a wide-angle 18mm frame can be shot followed by re-framing using the zoom at, say, 48mm or 55mm - and all without so much as moving from the same spot.
This reduces the need to swap between lenses when shooting, with some zoom lenses covering such a wide range there may be little reason to ever change lens.
On the downside, the more basic zooms such as Panasonic's 14-42mm f/3.5-5.6 Micro Four Thirds lens often have limited aperture control, in this case no brighter than f/3.5 at the wide end and, due to the optical constraints, even less bright at f/5.6 at the long 42mm end of the zoom.
Fixed aperture zooms are available, but these are often far larger, heavier and considerably more expensive.
Kit lenses are basic zoom lenses most frequently boxed up with a camera body at the point of purchase. Micro Four Thirds cameras tend to come with 14-42mm optics, while most APS-C DSLRs come with 18-55mm lenses.
In recent years, more advanced models have often come boxed up with more versatile lenses, such as the Nikon 18-105mm f/3.5-5.6 coming with the Nikon D7000.
Optical constraints and moving lens parts often mean image quality and sharpness from zoom lenses may be at its best at a particular focal length - such as (hypothetically) an 18-55mm lens producing its sharpest images from 28-40mm.
Often a zoom's sharpness won't match up to a prime lens, which is among their bigger downsides. If you want that extra lick of optical quality and greater aperture control through a similar focal length range, then lenses such as Tamron's 28-75mm offers a fixed f/2.8 wide aperture at all focal lengths and is a great step-up option to replace a more basic kit lens.
Typical kit or standard zoom lenses
Canon EF-S 15-85mm f/3.5-5.6 IS USM - £609
Nikon Nikkor 18-105mm AF-S DX f/3.5-5.6G ED VR - £225
Sony A-mount 28-75mm f/2.8 SAM - £629
Pentax SMC DA 18-135mm f/3.5-5.6 ED AL IF DC WR
Tamron SP AF 28-75mm f/2.8 XR Di - £358
Panasonic Lumix G Vario 14-42mm f/3.5-5.6 Micro Four Thirds - £124
Samsung NX 20-50mm f/3.5-5.6 ED - £153
Sony E-mount (NEX) 18-55mm f/3.5-5.6 OSS - £240
Wide-angle zoom lenses
Wide-angle zoom lenses
Wide-angle zooms are as per usual zoom camera lenses, albeit with a focal range typically in the 12-24mm or 16-25mm region. The zoom capacity enables you to adjust the focal range, which adds extra versatility compared to a wide-angle prime lens.
However, these lenses are often of premium build quality and the number and type of lens elements required to counteract barrel distortion makes them an expensive purchase.
Wide-angle zooms are a favourite for landscape photographers, because the ability to adjust framing via zoom from the lens instead of repositioning the camera can make or break whether a shot is even possible.
Sigma makes the world's widest-angle zoom lens, the 8-16mm f/4.5-5.6, or its popular 10-20mm f/4.0-5.6 has long been a staple lens for many landscape snappers.
Barrel distortion will cause slight bloating to the centre of the frame, however, plus horizontal and vertical lines close to the edge of the frame may not be perfectly straight. There are post-processing profiles to counter against this type of distortion, but it does come at the slight expense of sharpness.
Read our Best wide-angle lenses: 8 tested article
Typical wide-angle zoom lens examples
Nikon AF-S ED 14-24mm f/2.8G - £1,317
Sigma 8-16mm f/4.5-5.6 DC HSM - £549
Olympus Zuiko Digital ED 4-14mm f/4 Four Thirds - £1,550
Panasonic Lumix G Vario 7-14mm f/4 Micro Four Thirds - £1,049
A very popular choice for the keen amateur, superzoom lenses are a great example of why DSLRs are considered pro-spec cameras. A superzoom lens typically varies from a wide or medium focal length through to a telephoto, such as Tamron's 18-270mm f/3.5-6.3 travel zoom.
The drawback? Image quality can suffer due to the demands of the lens - asking for perfectly placed optics for the finest sharpness throughout the focal range is a tall order.
Furthermore, as per any zoom lens, the more affordable options have limited aperture control where the maximum aperture value often decreases as the focal length increases.
Of course there are higher-end models that tend to focus on a tighter focal length, such as the pro-spec Nikon 70-200mm f/2.8G. This is a grand example of a lens that's able to maintain top quality throughout its focal range, although at £1,650 we'd expect nothing less. Here an f/2.8 aperture is constant throughout. Internal focusing is also employed, meaning that the lens is always the same size and the focus ring won't auto-rotate while the autofocus hunts for its subject.
More often than not, an image stabilisation system (IS) is employed, which can move the internal lens elements by microscopic amounts to counter for handshake - something essential to help steady up when framing at longer focal lengths.
Superzooms are popular for a variety of subjects because they cover a wide range that makes shooting portraits through to more distanced work such as sport and wildlife a breeze.
Read our Best travel lenses: 8 tested article.
Typical superzoom lens examples
Nikon Nikkor 70-200mm f/2.8G ED VRII AF-S - £1,633
Canon EF 70-300mm f/4-5.6 L IS USM - £1,153
Pentax SMC DA* 60-250mm f/4.0 ED IF SDM - £1,049
Tamron 18-270mm f/3.5-6.3 Di II VC PZD - £499
Sony A-mount 75-300mm f/4.5-5.6 DT - £195
Olympus Zuiko Digital ED 50-200mm f/2.8-3.5 SWD Four Thirds - £1,000
Panasonic Lumix G Vario 100-300mm f/4-5.6 Micro Four Thirds - £458
Samsung NX 50-200mm f/4-5.6 ED OIS II - £170
Sony E-mount (NEX) 55-200mm f/4.5-6.3 OSS - £300
Macro is often used as a loose term to describe close-up photography. Technically speaking, a macro lens is one able to produce an object of actual size or greater on a camera's sensor, termed as a 1:1 or 1.0x macro lens.
However, many lenses not capable of this magnification are still labelled as macro lenses, while Nikon's micro classification adds to the terminology confusion.
A macro lens is designed to focus closer to the subject than a normal lens, with the likes of Canon's 60mm macro able to focus just 20cm from subject.
By moving the subject closer to the lens (or vice versa) the magnification is increased to enlarge a subject, but when shooting trickier subjects such as live bugs, a little more working distance may be required. In such situations the likes of Tokina's AT-X 100mm f/2.8 Macro is able to focus with 30cm between the subject and focal plane or Nikon's 200mm f/4 Micro can muster 50cm.
At full 1:1, a typical working distance is going to be less than 30cm from the end of the lens and the subject, which makes getting cracking shots all the trickier.
Intricate details are pronounced in macro shots, but the close-up nature of the subject means depth of field collapses into a very narrow window. You can forget about using super-wide apertures for macro shots.
Indeed many pros will stop right down to f/22 and add electronic macro flash to the front of the lens for increased shutter speed and, therefore, greater control.
Read our Best macro lens: 8 tested article
Typical macro lens examples
Nikon Nikkor 200mm f/4 AF Micro - £1,124
Olympus Zuiko Digital 35mm f/3.5 Macro Four Thirds - £210
Panasonic 45mm f/2.8 Macro Leica D Vario Elemar Micro Four Thirds - £600
Samsung NX 60mm f/2.8 ED OIS SSA Macro - £530
Sony E-mount (NEX) 30mm f/3.5 Macro - £230
Tilt and shift lenses
Tilt and shift lenses
Here's where things get that extra bit special. Shift camera lenses are used primarily to correct for converging vertical lines in architectural photography, while the provision to tilt adds full focal plane control. The two movements aren't mutually exclusive, although modern-day lenses, such as the Nikon 45mm f/2.8 PC-E and Canon EF 24mm f/3.5L TS-E, feature control over both.
Shift is the physical rise or fall of a lens from its standard position. Rather than tilting the camera upwards to shoot a tall building, for example, maintaining a parallel frame to the subject and shifting the lens upwards can be used to, as such, 'aim' the camera instead. This stops converging vertical lines by lowering the centre point's position to far lower in the frame.
Tilting a lens adjusts the way the focal plane sits to the sensor. While a normal lens sits parallel to the imaging sensor and, therefore, the focal plane runs directly across it, a lens with horizontal tilt has the capacity to move the focal plane through horizontal depth.
This can be used to make a wide-angle scene appear miniature - a current craze with various post-production software and smartphone apps - but is more useful for its proper use of front-to-back focus of a specific non-horizontal surface.
DSLR lenses usually lack both horizontal and vertical tilt control - something reserved for large format studio cameras where full three dimensional focal plane control can be obtained.
You need to know exactly what you're doing with these lenses to get full control, plus they're far from cheap - upwards of £1,000, if not closer to £2,000 a piece.
But the control you can obtain is far beyond that possible in post-production, and may be essential for studio or architectural professionals.
Typical tilt and shift lens examples
Nikon Nikkor ED 45mm f/2.8 D PC-E Micro - £1,394
Canon TS-E 24mm f/3.5L II - £1,720
Older Sony Minolta 35mm f/2.8 shift lenses are available second hand - but very hard to find
Older '70s Pentax 28mm f/3.5 shift lenses are available second hand - but very hard to find)
MC ARAX 35mm f/2.8 tilt shift (Nikon F, Canon EF, Sony A, Pentax K, Olympus 4/3 and other fittings including Leica R)
Liked this? Then check out Best DSLR: top cameras by price and brand
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