Zoom zoom!

Matthew Richards takes a look at eight fast telephoto zooms to discover which has the best go-faster credentials

There are some good ‘budget’ telephoto zoom lenses on the market. Nikon’s AF-S 70-300mm f/4.5-5.6G VR (£520/$500) is the best in class, while the Tamron SP 70-300mm f/4-5.6 Di VC USD (£300/$450) is a top bargain buy. But one thing that all so-called budget tele-zooms tend to share is a variable aperture rating that shrinks as you extend through the zoom range, typically down to f/5.6 at the long end.

Expert and professional photographers generally prefer ‘constant-aperture’ zoom lenses wherever possible and, in the case of telephoto lenses, are often willing to sacrifice greater telephoto reach in order to get it. The favoured choice is therefore a 70-200mm zoom, with a faster f/2.8 aperture rating. At the long end of the (albeit slightly shorter) zoom range, they’re two stops faster than f/5.6.

Even at a directly equivalent 200mm zoom setting, most 70-300mm lenses are still nearly two stops slower.

Bonuses of the wider aperture rating are two-fold. First, you can gain faster shutter speeds without the need to ramp up the ISO. This is ideal for freezing the action in sports and wildlife photography, in anything other than bright sunlight. Second, a wider aperture provides a tighter depth of field, enabling you to throw the background further out of focus and really isolate your subject. For this reason, fast telephoto lenses are often favoured for portraiture at weddings and other events, where light levels can be quite low, and where you need the versatility of a zoom lens.

A less-obvious advantage of constant-aperture zoom lenses is that, when you’re shooting in manual mode, you can set the lens to its widest available aperture and be sure that it’s not going to change when you extend the zoom setting.

The majority of lenses in this month’s Big Test have an f/2.8 aperture rating. This means that you can fit a 1.4x teleconverter to gain nearly a 300mm focal length (280mm to be precise) and still enjoy a relatively fast f/4 widest aperture. You can go further still, with a 2x teleconverter that delivers a super-telephoto 400mm focal length, while still only dropping to an f/5.6 aperture rating, maintaining full autofocus compatibility with any Nikon DSLR. We should point out, that while Tamron usually suggests the use of Kenko teleconverters with its lenses, these aren’t compatible with the 70-200mm VC USD lens on test. Tamron’s brand-new 70-200mm G2 (second-generation) lens is compatible with Tamron’s own latest teleconverters, but the Nikon-fit edition wasn’t available for review by the time we went to press.

Handling is refined in all of the lenses in our test group, compared with variable-aperture lenses. With fully internal zoom and focus mechanisms, the physical length of the lens remains fixed throughout the entire zoom and focus ranges. (You’ll notice that with a 70-300mm budget zoom, for example, the physical length nearly doubles as you sweep to the longest end of the zoom range.) Upmarket build quality also confers a more robust and hard-wearing construction, as well as smooth and precise operation of zoom and focus rings. All in all, a fast telephoto zoom is usually a significant step up the quality ladder, in terms of build, handling and allimportant image quality.

A wider aperture provides a tighter depth of field, enabling you to throw the background further out of focus and really isolate your subject