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Tuesday, June 8, 2010

One Lens To Shoot Anything

Big-range zooms (10x and more) aren’t just for travel anymore. With good sharpness and contrast across their focal lengths, today’s models are some of the most advanced optics on the market and they’re designed for digital.

Labels: Lenses

This Article Features Photo Zoom

Outdoor photographers have long sought the “do-it-all” lens, a single unit that could handle everything from wide-angle to telephoto and close-ups. Camera and independent lens manufacturers have responded to our needs with superzooms designed specifically for DSLRs with APS-C and Four Thirds image sensors by making a number of 10x-plus zooms that are ideal for traveling light and give you lots of options for framing anything from a travel scene to a bird in flight to a majestic landscape. Today, the range includes 18-200s, 18-250mm and even an 18-270mm (which, despite its amazing 15x zoom range, measures just 3.1x3.9 inches at the wide-angle setting and weighs under 20 ounces—remarkable considering it provides 35mm-camera-equivalent focal lengths from 27-405mm!). These super-range superzooms even focus down to under 20 inches. And did we mention that the superzooms give you all those focal lengths in that compact package for well under $1,000?

Yes, the superzooms are versatile, easy to carry and affordable. So what’s the catch?

Benefits And Drawbacks
Superzooms by their very nature require a series of design compromises. It’s difficult enough to correct a prime (fixed-focal-length) lens to be sharp and aberration- and distortion-free at its single focal length. With a zoom, designers have to correct for aberrations and distortion at a wide range of focal lengths, and correcting an aberration at one focal length can make that aberration or another one worse at another focal length. Today’s designers use high-tech materials, aspherical and extra-low-dispersion elements, and computer-aided design to produce amazingly good performance throughout a very wide focal-length range.

The 10x designed-for-digital superzooms can be a one-lens solution for many nature photographers. Long favored for travel photography, today’s lenses also can be used for landscapes, macro and even wildlife.
Still, the superzooms don’t produce quite the image quality of top prime (single-focal-length) lenses of equivalent focal length—a given manufacturer’s 28mm wide-angle lens will produce sharper images with less distortion and vignetting than the same manufacturer’s 18-200mm zoom at 28mm, and the manufacturer’s 200mm prime telephoto lens will produce better image quality than its 18-200mm superzoom at 200mm. But each prime lens can cost more than the superzoom, and you only get the single focal length. It’s a trade-off, and many find the cost and convenience of the superzoom more than offset the slight loss of image quality.

Superzooms are also slower than primes. Most wide-angle primes have a maximum aperture of ƒ/2.8 or faster, as do most 200mm telephoto lenses, while most superzooms have a maximum aperture of ƒ/3.5 at the wide end and ƒ/5.6 or ƒ/6.3 at the long end. This means you’ll be better off with primes if you specialize in handheld low-light photography or like to do selective-focus work at wide apertures.

But superzooms remain popular. Besides convenience, space and cost savings and ease of travel, superzooms offer a couple of other advantages over prime lenses. For one thing, they help keep your sensor free of dust because you won’t have to change lenses nearly as often as when using primes. For another, you can set intermediate focal lengths. Even if you have a whole complement of prime lenses on hand, the ideal focal length for a particular shot might be between them. And being able to change to any of the focal lengths with a quick twist of a wrist will help you fine-tune compositions and capture those decisive moments you’d miss if you had to change lenses as the moment happens.


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