Fixed Focal Length
Fixed lenses offer some advantages over zooms. They’re generally smaller and lighter, with wider maximum apertures and superior image quality. An ultra-fast (e.g. f/1.8) 50mm lens is perfect for low light, 85-105mm is ideal for portraits, while a fast 300mm (or longer) tele is a popular addition to any wildlife or sports shooter’s kit.
Most DSLRs come with a standard zoom; that is, one which spans the focal range from moderate wideangle to short telephoto. These ‘kit’ lenses are generally fine for most purposes, but there are alternatives that offer superior image quality and/or wider maximum apertures – at a price premium, of course.
Wideangles make subjects appear further away, enabling you to get more in the shot. Among the most popular wideangle zooms are the 10-20mm/12-24mm and 17-35mm ranges. Superwide lenses cause more distortion, especially when tilted off the perpendicular but, with care, can be used to inject drama into your photographs.
Telephotos make subjects appear closer. They’re ideal for sport and wildlife, where it’s more difficult to get as close as you’d like, while short teles are good for portraits. Telephotos increase the risk of camera shake, so consider one with Image Stabilisation if your camera doesn’t have it, or a wide maximum aperture.
Want a one-lens solution for your photography? Get a superzoom. While they rarely compare with shorter range lenses as far as image quality is concerned, an 18-200mm type lens offers the benefit of speed, convenience and a dust-free sensor. Good for general shooting at moderate print sizes.
Many lenses misleadingly feature the ‘macro’ moniker but a true dedicated macro lens lets you get close enough to reproduce your subject at life-size (or half life-size) on the sensor. Macro lenses (few of which zoom) come in a range of focal lengths, from standard to telephoto.
Narrowing down the field
There are hundreds of lenses but only a few will fit your camera. Each camera manufacturer has its own lens mount, and lenses designed for one lens mount will not usually fit other manufacturers' cameras. Sigma, Tamron and Tokina lenses will fit a variety of mounts, but you must buy the lens in the right mount. While adaptors will enable lenses of one mount to be fitted to cameras of another, there is often a loss of some functionality.
Each camera manufacturer has their own lens mount and they aren’t compatible with one another. If you own a Canon, for example, you can’t use Nikon lenses, though you can use independent brands such as Sigma and Tamron – if you purchase them in the right mount.
If you’re migrating from a 35mm SLR, your lenses won’t provide the same field of view on a DSLR unless you have a ‘full-frame’ model such as Canon’s EOS 5D. For Nikon, Pentax, Fuji and Sony DSLRs, magnify the focal length by 1.5x to get the 35mm equivalent (eg a 100mm lens becomes 150mm); for Canon it’s 1.6x; Sigma is 1.7x; and the Four-Thirds mount, 2.0x.
You pay a premium for lenses with wider maximum apertures, but for many users they’re worth it. Wider apertures mean you can use faster, motion-stopping shutter speeds, and shoot handheld in available light with less camera shake. Zooms whose maximum apertures are fixed throughout the range (instead of getting smaller as you zoom) also cost more.
Most digital sensors are smaller than 35mm, which is why lenses designed for digital can be smaller than those designed for 35mm. Although pre-digital lenses can be used on digital SLRs they may not perform as well, due to their optical characteristics. Lenses designed solely for digital sensors, however, can’t be used on 35mm cameras (or digital SLRs with 35mm-sized sensors) because the image they produce isn’t big enough in diameter to cover the sensor/film, causing severe vignetting.
It’s impossible to hold a camera dead steady without support, but at the faster shutter speeds any shaking isn’t noticeable in pictures. As the shutter speed drops, though, our pictures become progressively less ‘crisp’ until they’re downright blurry. Optical Image Stabilisation (used by Canon) and Vibration Reduction (Nikon) technologies use a floating element inside the lens and a gyroscope to compensate for our body movement. It’s effective enough to give us two or three extra stops of extra shutter speeds to play with before shake becomes visible. Some cameras (e.g. Sony, Pentax, Samsung and Olympus) use a moving sensor instead, so IS/VR lenses aren’t necessary.
Buiilt-in Focus Motor
Some lenses incorporate a motor within the lens to drive the auto focusing, while others are powered by motors within the camera. Lenses with their own motors will generally focus more quickly than those without. Some cameras, such as the Nikon D40, don’t have a built-in focus motor so in these cases you can only use lenses that have their own. Canon brands its lens motors USM (Ultrasonic Motor), Sigma calls its HSM (Hypersonic Motor) and Nikon’s are called Sonic Wave.
Most lenses have letters as part of their names. These usually denote what technology they feature and how sophisticated they are. For example, manufacturers who incorporate image stabilisation or low-dispersion elements in their lenses usually state this as part of the lens’s name. Other information gathered from these letters may be the type of mount the lens uses, whether any aspherical elements feature and whether the lens sits in the company’s ‘professional’ range, which can include weatherproofing and sturdier constructions.
Your easy guide to lens suffixes:
II/III – Denotes version of lens
APO – Apochromatic lens elements designed to produce sharper images by focusing all wavelengths of light to the same point
DG – Sigma’s designation for digital and full-frame lenses
Di – Tamron lenses designed for full-frame sensors
Di-II – Tamron lenses compatible with APS-C sensors
DO – Canon lenses featuring a diffractive optical element
DX – Nikon lenses designed for APS-C sensors
ED – Nikon lenses featuring Extra Low Dispersion element(s)
ED – Olympus and Leica lenses with low dispersion glass
EF – Canon lenses compatible with full-frame and APS-C-sized sensors
EF-S – Canon lenses compatible with APS-C sized sensors
EX – Sigma ‘excellent’ range of lenses
FE – Canon’s fisheye lenses
G – Nikon lenses without a manual aperture ring
HSM – Sigma lenses with Hypersonic Motor
IF – Internal focusing lenses
L – Canon ‘Luxury’ range of lenses
LD – Tamron lenses with Low Dispersion glass
MF – Manual-focusing-only lenses
OS – Sigma lenses with Optical Stabilisation
PRO – Tokina Professional range of lenses
TS-E – Canon’s ‘tilt and shift’ lenses
UD – Canon lenses with Ultra Low Dispersion element(s)
VR – Nikon lenses with Vibration Reduction
USM – Canon lenses with an Ultrasonic Motor