Lenses are the single most important aspect of any photographer’s kit bag.
That’s right. It’s not sensors with gigantic megapixel counts, or having the latest model number, or even the highest frame rate. While they all have their place and use, it is the lens you use when you take a photograph that will have the biggest impact on the way the final image actually looks.
Lenses come in a huge range of focal lengths, maximum apertures and purposes – and a truly mind-boggling array of prices. Each and every one will have its strengths, weaknesses, characteristics and primary uses, and this time out we are going to look at how to get the best out of everything from humble ‘kit’ lenses through to more exotic zooms and primes.
Get a Grip
Let us think about the factors that come in to play when you make a photograph in terms of lenses:
- The focal length you are using
- The focus distance
- The f-stop the lens is set at
- The exposure mode the camera is set to (and thus exposure time)
Each one has an important influence on the look of the final shot, but if you think for a moment, you will realise there are yet more factors which can be even more important than the camera-technicals. Are you holding the camera correctly? How steady is the camera as you actually push the shutter button? All of these factors can lead to blurred or shaky images – easy to blame on the lens, but similarly easy to eliminate with good basic technique.
Good camera technique starts with a solid, stable grip on the camera itself; the steadier you can hold it the more reliable your shots will be.
Always wrap as many fingers around the grip on the shutter-side of the body as will fit comfortably, and as you are ready to press the shutter button do not be afraid of squeezing with your thumb on the back of the camera firmly to lock your hand tightly.
You should always support the lens with your left hand – do not be tempted to hold the other side of the body. Cradling the lens with your palm like this will give you the most stable platform possible.
As a rule of thumb, you can assume you will always get a sharp image with an exposure time of 1/focal-length. So, for a 50mm lens that equates to a 1/50th second exposure and for a 200mm lens, 1/200th second and so on, as the exposure is fast enough to cut out ‘typical’ vibration.
However, there is another top-tip to use if your exposure time in a given situation is close to this limit – breathe like a sniper! Whilst it may sound rather far-fetched, thinking about your breathing as you press the shutter can significantly impact the stability of the camera. As you are about to take the shot, draw in a deep breath and exhale slowly. Press the shutter button at the bottom of your outward breath and your torso and arms will naturally be relaxed and at their most stable.
Using this technique, and with a good grip, it is perfectly possible to get sharp shots (without a tripod), at 1/15th seconds using a 50mm lens, and 1/50th using a 200mm lens – very handy in low-light situations.
Before we move on, let us quantify the terms we will use – sharpness, unsharpness and softness. Sharpness refers to the image being in perfect focus and rendered crisply. However, the two other terms are distinctly different. Unsharpness is caused by a problem in the way the exposure has been made – the lens might be out of focus, the camera was shaken or moved as the shutter was clicked, or even a zoom ring nudged during the exposure. Softness, on the other hand, is caused purely by the lens not behaving properly.
A famous photographer once said, ‘any good, modern lens is corrected for maximum definition at the larger stops. Using a small stop only increases depth (of field)’. Given that was Ansel Adams (all the way back in 1937), you would assume that you can shoot any lens, any way, and get peak performance – and modern lenses produce great shots without much difficulty.
However, every optical design is in some sense a compromise. Fast lenses require very precisely ground, large elements in perfect alignment, zoom lenses need to focus accurately and deliver a sharp image across a potentially huge range of focal lengths and so on. Understanding how to be sympathetic to the compromises of a particular lens will yield great results.
The simplest way to sharpen up your shots (beyond good grip technique), is to ensure accurate focus. Using the correct autofocus mode for the right situation is a great start, for instance AF-C or tracking autofocus for moving objects, or learning how to focus lock (see boxout 2), with an off-centre subject is a crucial step in nailing the focus in every shot – even the smallest focus error can lead to unsharpness.
When using fast lenses or long telephoto lenses for portraits, a common instance of ‘critical’ focusing, it is a great idea to reset the focus between shots by focusing on something at a completely different distance before refocusing where needed.
In low light, try using the central focus point in the viewfinder, focus-locking and recomposing your shot (if desired), as the central focus point is often a ‘cross-type’ focus point which utilises a broader area, and measure in 2D rather than the simple vertical-only of ‘normal’ sensors, and will be much more reliable in difficult conditions. Have a look in your camera’s manual to see where the cross-type sensors lay in your viewfinder.
A quick top tip for very poor conditions – try turning the camera 90 degrees, locking focus, and rotating back to the original position – you might be surprised how much of a difference it can make!
The aperture you use will also have an impact on the final sharpness of your shot. Whilst modern lenses generally perform well ‘wide-open’, it is an inevitability that this will not be the ‘sharpest’ aperture, as the light gathered on to the sensor has to pass through the very edges of elements inside the lens barrel. Stopping down the lens a little will almost always sharpen up a lens.
As a rule of thumb, lenses perform at their very best between two and three stops down from their maximum aperture, be they kit lenses or many thousands of pounds-worth of exotic f/2.8 zoom or super-telephoto.
In the case of a variable aperture kit lens, take two stops down from its ‘middle’ maximum aperture – f/4. If you now stop the lens down to f/8, you will be certain to hit the peak performance in terms of sharpness that the lens can produce. For prime lenses, the peak sharpness often lies between f/4 and f/5.6 depending on how ‘fast’ the lens is to begin with.
Try taking two shots and comparing, looking at a landscape, focus at infinity and take one shot at the maximum aperture the lens can produce. Next, stop the lens down to f/8, refocus on infinity and take the same composition. Viewed at 100% on-screen (i.e. full zoom without enlargement), you will see a marked difference between the two shots. Using the ‘correct’ aperture like this will rid any lens of softness.
However, doing this is a compromise in itself – you might want to blur backgrounds using a wide aperture (shallow depth of field), or get more of the shot in focus stopping right down to minimum aperture (usually around f/22 in a zoom, deep depth of field).
If either of these ‘looks’ are what you are going for, then do not get caught up in worrying about sharpness – getting the feel of the shot right is actually far more important.
As a final top tip, beware of stopping down your lens too far to increase depth of field. Whilst it is tempting to set apertures like f/16 or f/22 to get absolutely everything in focus, you will actually find that you are introducing softness because of an optical property called diffraction. Think of squinting through mostly closed eyes – that is diffraction, and closing the aperture introduces similar effects!
Try using apertures around f/9 – f/13 and focus slightly in front of infinity for a sharp landscape shot from front to back of the image. This technique is called hyperfocal focusing and is worth researching and experimenting with.
The Right Tools For The Job
Looking at a camera retailer’s website or catalogue will show you a bewildering array of lenses available – one particular manufacturer’s range covers 10mm through to 800mm, and prices from £109 to £14,000. If you are looking to expand the range of glass in your camera bag, it can be difficult to know what to look at first, so we are going to take a look at some great options. Firstly, it is worth discussing a singular choice – picking a zoom lens or a prime (fixed focal length).
Zooms offer the most flexibility, (with some ‘super-zooms’ covering a huge focal range – such as 18-300mm in one go!), but all zooms are an optical compromise requiring a lot of different bits of glass to work well together across the focal range. Cheaper zooms tend to have more limited focal range and vary their aperture as you zoom. The most expensive types of zoom have a broader range and/or a fixed aperture.
Expensive (typically f/2.8) zooms work extremely well, and can produce fabulous images, but shockingly a £1,300 mid-zoom (24-70mm f/2.8) at f/2.8 is not as sharp as a bargain-basement £100, 50mm f/1.8 stopped down to the same aperture.
Primes give you a fixed window on the world but lack the fundamental flexibility a zoom provides. Primes are often faster (f/1.4, f/1.8, f/2), and in many cases avoid the compromises that zooms have to live with, leading to sharper images – and as they are fast, shallower depths of field are on offer. Primes can have an alarming price gradient, however, with top-end specialist (24mm, 85mm) lenses starting around the £1100 mark (Nikon/Canon) running up in to the tens of thousands for super telephotos.
Stepping up from a kit lens, you can expand the focal range and improve performance wide-open by looking at the 18-135mm range offered by Nikon, Pentax and Canon. Each of these lenses performs very well, maintaining a good wide-angle starting point and adding a short telephoto range on top of a kit lens.
In the same vein of a ‘do-it-all’, one lens solution, all of the big manufacturers offer a super-zoom generally covering 18-300mm at around f/3.5-6.3. These lenses are perhaps the single most flexible bit of kit you can add to your bag, but note they are slow at the telephoto end (requiring either good strong light or higher ISO settings to maintain usable shutter speeds), and if you compare the results to either a dedicated wide-angle 18mm lens or 300mm telephoto it will be obvious that it is a compromise.
However, that said, if your aim is to only carry one lens all day, these certainly fit the bill and allow you to shoot under many different circumstances without reaching in to the kit bag.
Moving in to more specialist territory, all of the big manufacturers offer ultra-wide zooms. These lenses start at 10mm (for a DX or APS-C sensor, 14mm for a full-frame sensor), and may zoom out to 20, 22 or 24mm. Adding an ultra-wide to the bag can provide some unique perspectives – the extreme angle of view these lenses can show the world in a way the human eye does not normally see, emphasising foreshortening and distance, and capturing vast panoramas in a single shot. I love ultra-wide lenses, but beware, as it is very easy to produce shots with weak composition as there is so much to consider whilst framing. Typical ultra-wide zooms weigh in around £350-600, depending on manufacturer.
Reaching out into the range of telephotos all of the big brands offer reasonable telephoto zooms (some under £300 for a 55-200mm DX/APS-C only), that add a lot of reach to your armoury without some of the compromises of a do-it-all lens. If you are prepared to spend around £1000 on a telephoto, 70-200 f/4 zooms are a superb choice. Despite the relatively slow aperture they are optically brilliant (truly stunning sharpness), and will last a lifetime thanks to great build quality.
Macro lenses are not necessarily an obvious choice unless you want to do close-up photography – and that is what they excel at. However, macros typically have a medium-fast aperture (f/2.8) and are a generally razor sharp – whilst they are intended to get in close or very, very close, they actually can make great portrait lenses as well.
Typical focal lengths of macro lenses are 40, 50, 60, 85, 105, 180 and 200mm. The longer end of the spectrum gets very expensive, but a £650 105mm macro could also act as your telephoto and main portrait lens. They are much more versatile than you might think and are well worth investigating.
If I were to recommend buying one lens beyond a kit 18-55mm, I would strongly suggest either a 35mm f/1.8 (Nikon), or 50mm f/1.8 (Canon/Pentax). These lenses give you a fixed point of view you can learn to ‘see’ at all times, and thus frame quickly and accurately. They are all technically superb, very sharp, lightweight and cost around the £100-150 mark.
An f/stop is, mathematically speaking the ratio of the focal length of the lens to the size of ‘entrance pupil’ or diaphragm of a lens. More practically, it dictates how ‘bright’ a lens is, and the depth of field the lens can produce.
A ‘stop’ is a relative quantity denoting a doubling or halving of light transmitted through the lens to the sensor. Expressed as a geometric sequence, this is not an obvious set of numbers to remember, but standard stop ratios are f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45 and so on.
Maximum aperture denotes the maximum amount of light the lens can let through and, as a related property, the depth of field/focus the lens produces ‘wide-open’ (at maximum – largest physical size, lowest f/stop setting – aperture). ‘Fast’ lenses are typically around f/1.4, f/1.8 and f/2. ‘Slow’ lenses are often considered to be around f/5.6 to f/11.
The larger the maximum aperture (lower f/number), the shallower the depth of field of the lenses when wide open.
depth of field
The distance in front and behind the exact point of focus of the lens. Shallow depth of field may only have a depth of millimetres, deep depth of field may be many centimetres through to tens or more metres.
Focus locking is a simple but massively useful technique you can use on any dSLR, mirrorless or micro 4/3rds camera, especially in poor light.
- Set the focus point to the centre and aim at the object you want to focus on
- Half-depress the shutter button until the focus confirmation light/dot/beep happens
- Keeping the button half-depressed, recompose the shot as desired
- Smoothly fully press the shutter button to take the photo
Focus locking allows you to use the most sensitive focus sensors (cross-type) whilst giving you the flexibility to compose exactly as you wish.