A quick guide to what to look out for when buying a telephoto zoom lens for your camera.
Zoom range
A 50-200mm lens will give you an effective zoom range of 75-300mm, whereas a 70-300mm model provides a more powerful telephoto reach of up to 450mm.
Image stabilisation
Not all lenses have optical stabilisation, though many of the latest Nikons, Sigmas and Tamrons offer it equivalent to four stops, for sharp handheld shots.
Autofocus motor
Standard electric motors are often quite noisy and slow. Ultrasonic ones are quieter and faster, while ring-type ultrasonic systems are the fastest, and nearly silent.
Shutter release
A shutter release prevents you destabilising the tripod when you press the shutter and with prices under £30, there's really no excuse not to get one. If you don't have one to hand, you can try using the self-timer – just be prepared to make several attempts if the lighting conditions change.
Maximum magnification
At their closest focus distances, the Sigma 70-300mm APO and Tamron 70-300mm AF lead the way with a 0.5x macro facility. The maximum magnification of other lenses in the group is about 0.25x.
Maximum aperture
The largest aperture on budget telephoto lenses is usually f/4 or f/4.5 at the shortest focal length, reducing to f/5.6 at the maximum zoom setting.
Sensor type
Nikon FX, Sigma DG and Tamron Di lenses are fully compatible with both full-frame and APS-C camera bodies. DX, DC and Di II lenses are designed specifically for APS-C cameras and produce smaller image circles.
Shooting tips
Fit a filter
When you're shooting into the distance with a telephoto, haze in the atmosphere can degrade your photos. A UV filter can help, and will also protect the front lens element from scrapes and scratches. Check the filters size before you buy.
Use the lens hood
All the lenses on test come complete with a hood. With telephoto shots, these can greatly reduce ghosting and flare. Lenses that use internal focusing have petal-shaped hoods, reflecting the fact that their front element doesn't rotate.
Normal vs Active VR
Some Nikon lenses feature Normal and Active modes in their Vibration Reduction system. Normal is for regular use, while Active is meant to be used when you're shooting from a vibrating platform such as a moving train or car.
