Tuesday, April 29, 2014
The Medium Mainstay
Big telezooms get the glory and wide-angle models get the headlines, but the underappreciated middle child in a typical three-zoom kit may be your most useful lens. Learn how to choose the right one for you.
Wide-angle lenses, especially fast ones, tend to suffer from spherical aberration and distortion, and longer lenses from chromatic aberrations. With spherical aberration, light rays coming through the edges of the lens aren't focused at the same point as rays coming through the center. With chromatic aberration, different colors (wavelengths of light) are focused at different planes. Both reduce image sharpness.
Today's lens makers combat these by using special lens elements. Aspherical elements counter spherical aberration and distortion, providing sharper images and also allowing for the design of more compact lenses. Low-dispersion and extra-low dispersion elements (called ED, UD, SUD, ELD, SLD, FLD and the like by the various manufacturers) counter chromatic aberrations, also delivering sharper images. All of the zooms in the accompanying chart feature special elements in their construction; the more costly lenses generally offer more effective ones (i.e., they do a better job of minimizing aberrations and distortion).
Larger filters cost more than smaller ones, so you may want to consider that when selecting a mid-range zoom if you use a lot of filters. The ƒ/2.8 lenses tend to take larger filters, as they must be larger in diameter to provide their faster maximum apertures.
If you have more than one lens, it's nice if they all take the same filter size so you can use the same filters on all of them—another consideration when buying a new lens if you have a lot of filters. Of course, you can use adapter rings to mount larger filters on smaller lenses, but if the new lens takes larger filters than the ones you currently own, you'll have to buy new filters for it.
Faster lenses generally cost more than slower ones, another consideration when selecting the right one for your needs. Mid-range zooms start at around $500 and go up beyond $2,000. The more costly ones tend to be faster, better optically, bulkier and more ruggedly built. If your budget doesn't permit purchasing a high-end lens, the lower-cost ones make good options.
A good mid-range zoom costs much less than separate wide-angle, normal and short telephoto prime lenses of equal speed (i.e., ƒ/2.8 or ƒ/4). This can save you a lot of money, along with the speed and convenience factor. You can change framing merely by rotating the zoom ring rather than having to mount another lens. And minimizing lens-changing also reduces the opportunities for dust to enter the camera body and settle on the sensor assembly.
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