A main attraction of any DSLR is that you can fit the ideal lens for pretty much any shooting scenario. But this isn't without its pitfalls. Most of us are rightly concerned about swapping lenses in dusty environments, dumping dirt into the camera body that can often find its way onto the image sensor.
And with fleeting photo opportunities, there's always the risk that the moment will have passed before you've finished removing one lens, fitted another and taken aim.
There are also times when you might need to travel light, and it's not just about baggage allowances when you're going on holiday. Anything from city wanderings to countryside rambles and hill-climbing can become an arduous challenge when you've got a big bag stuffed with heavy lenses hanging off your shoulder.
Wouldn't it be nice if you could just carry a single lens that answered almost every photographic need? Enter the superzoom.
The whole idea of these lenses is that they deliver everything from a wide-angle field of view to serious telephoto reach, all at the flick of a wrist. There are two main types - those designed for APS-C-format cameras from the D3100 to the D300s, and full-frame lenses for bodies such as the D700 and D4.
Nikon calls these two types 'DX' and 'FX' lenses respectively. With Sigma, it's 'DC' and 'DG', and for Tamron it's 'Di II' and 'Di'. But if you're using an APS-C-format camera you needn't let lens type be the deciding factor; full-frame lenses are compatible with smaller-sensor bodies.
If you want a really wide-angle focal length on an APS-C-format body, you'll need an APS-C-format lens. Once you take the 1.5x crop factor into account, an 18mm focal length effectively becomes 27mm.
However, a lens such as the Nikon 24-120mm f/3.5-5.6G AF-S IF-ED VR still equates to 36mm at its widest zoom setting, which is practically identical to the 35mm focal length of a wide-angle lens.
Sure, the maximum effective telephoto reach of 180mm isn't all that impressive either, but that's not the whole story.
A fine balance
The bigger the zoom range, the more image quality is likely to be compromised. Outright sharpness might be impaired, and distortions are likely to be more noticeable.
So while a lens such as the Tamron 18-270mm f/3.5-6.3 Di II VC PZD gives a class-leading 15x zoom range, equivalent to 27- 405mm, you push the boundaries of what's possible when you also demand high optical quality.
Naturally, if you're not too fussed about wide-angle shooting, a full-frame 28-300mm lens goes extra large on telephoto reach when fitted to an APS-C-format camera. Even so, the minimum effective focal length of 42mm is not wide enough for most of us.
But if you're considering trading up to a full-frame body in the future, any full-frame lenses you buy now will be suitable.
Speed is another issue, especially when it comes to maximum aperture. At their longest telephoto focal lengths, the Nikon 18-200mm, Nikon 24-120mm and Nikon 28-300mm tested here all have a maximum available aperture of f/5.6.
This means that under dull lighting conditions you'll be forced to use quite a slow shutter speed, unless you resort to increasing the sensitivity setting of your camera.
All other lenses on test are even slower at f/6.3 - under anything other than bright sunlight, camera- shake can be a big problem.
If you want to travel light with just a superzoom on your camera, lugging a tripod around defeats the object. Instead, try handheld shooting.
To fend off camera shake, all but the Tamron 18- 200mm in the group feature image stabilisation. Nikon calls its system VR (Vibration Reduction), Sigma has OS (Optical Stabilization) and Tamron has VC (Vibration Compensation).
All competing systems have a microprocessor- controlled group of lens elements that senses vibration and attempts to cancel it out by moving the group. It's worth having, as you get sharp shots quite consistently at shutter speeds up to three or four stops slower than you would without stabilisation.
Keep the noise down
Speed and accuracy are also critical factors when it comes to autofocus. All the Nikon lenses on test have fast, whisper-quiet, ring-type ultrasonic systems. These have the added benefit of boasting full-time manual focus override in Single-AF mode.
At the other end of the scale, basic electric motors are sluggish and noisy, as shown by the Tamron 18-200mm and 28-300mm lenses. All other lenses on test are based on ultrasonic motors. Unlike ring-type ultrasonic systems, these aren't much faster than basic electric motors, although they are quieter.
They're not as near-silent as ring-type systems, though, because gear wheels are still used to drive the autofocus.
