Need to Know

There are a few other things to bear in mind when choosing a lens - here are the main considerations.

LENS MOUNTS

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 get them in the right mount.

MAGNIFICATION FACTOR

If you're migration 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 (e.g. a 100mm lens becomes 150mm); for Canon it's 1.6x; Sigma is 1.7x; and for the Four-Thirds mount, 2.0x.

MAXIMUM APERTURE

You pay a premium for lenses with wider maximum apertures, but for many users the are 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 through the range (instead for getting smaller as you zoom) also cost more.

35MM COMPATIBILITY

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 sensor/film, causing severe vignetting.

ANTI-SHAKE

It's impossible to hold a camera dead steady without support, but at faster shutter our shakiness isn't noticeable in pictures . As the shutter speed drops though, our pictures become progressively less "crisp" until they are downright blurry. Optical Image Stabilization (used by Canon) and Vibration Reduction (Nikon) uses a floating element inside the lens and a gyroscope to cancel out our body movement. It's effective enough to give us two or three extra stops af 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.

BUILT-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 HSM (Hypersonic Motor) and Nikon's are called Sonic Wave.

SUFFIXES

Most lenses have letters as part of their names which usually denote what technology they feature and how sophisticated they are. For example, manufacturers which incorporate image stabilization 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 spherical elements feature and whether the lens sits in the company's "professional" range, which can include weatherproofing and sturdier constructions. For a list of the main suffixes, see the Need to Know box below.

	Need to Know Baffeled by the long names? Here's a guide to the main lens suffixes
	II/III -	Denotes version of lens		G -	Nikon lenses that don't have manual aperture ring
	APO -	Apochromatic lens elements designed to produce sharper images by focusing all wavelengths of light to the same point		HSM -	Sigma lenses with Hypersonic Motor
	DC -	Sigma's designation for APS-C sensor sized compatible lenses		IF -	Internal focusing lenses
	DG -	Sigma's designation for digital full-frame lenses		L -	Canon's "luxury"range of lenses
	Di -	Tamron lenses designed for full-frame sensors		LD -	Tamron lenses with Low Dispersion glass
	Di-II -	Tamron lenses compatible with APS-C sensors		MF -	Manual focusing only lenses
	DO -	Canon lenses featuring a diffractive optical element		OS -	Sigma lenses with Optical Stabilization
	DX -	Nikon lenses designed for APS-C sensors		PRO -	Tokina's professional range of lenses
	ED -	Nikon lenses featuring Extra Low Dispersion element(s)		TS-E -	Canon's "Tilt and Shift" lenses
	ED -	Olympus and Leica lenses with Low Dispersion element(s)		UD -	Canon lenses with Ultra Low Dispersion element(s)
	EF -	Canon lenses compatible with full-frame and APS-C sized sensors		USM -	Canon lenses with an Ultrasonic motor
	EF-S -	Canon lenses compatible with APS-C sized sensors		VR -	Nikon lenses with Vibration Reduction
	EX -	Sigma's "excellent" range og lenses