Walk into any major camera store, or check a retailer's Website, and one fact will immediately become evident. Zoom lenses greatly outnumber the single-focal-length or "prime" lenses. Some serious photographers are still wary of zooms, but others have switched almost entirely to such lenses. When you buy a kit, it will probably include a zoom instead of the 50mm lens that was typical at one time. Some purists, including many bloggers, frequently complain about this trend, insisting that prime lenses offer numerous advantages over zooms.
In Part 1, let's consider the arguments against zoom lenses. Next week, in Part 2, I'll discuss the benefits that explain why I now own only zoom lenses, with a single exception.
Image Quality Issues
Some photographers will point out that the optical performance of a prime lens is better than that of most zooms. As a rule, that's true. A 50mm lens that costs $125 will provide better edge-to-edge sharpness than a comparably priced zoom. If you own only a kit lens for example, try this: shoot in the f/8 to f/11 range as often as possible. (In outdoor photography that usually won't cause problems, especially if you make ISO 400 your standard setting.) Since those apertures provide the best image quality, use them whenever it's practical to do so.
Zoom lenses are also more prone to reduced image quality caused by flare: a hazy effect due to stray light striking the front element. And any zoom lens' hood is designed to accommodate the wider focal lengths, so it offers less protection against flare as you shift toward telephoto. In order to avoid problems caused by flare on bright days, change your shooting position relative to the sun so the light will not strike the front element. As well, remove any filter to further minimize the risk of flare. (Many zooms of some brands are sold without a lens hood. This is an essential accessory, so it's well worth buying one.)
Small Maximum Apertures
All affordable zooms are considered to be "slow." Their maximum apertures are often f/4.5-5.6 versus f/1.8, for example. In practical terms, that means that you'll need to use a longer shutter speed on an overcast day or in a dark cathedral, for example. And that does increase the risk of blurry photos caused by camera shake.
You can prevent that problem by switching to a higher ISO level. On an overcast day, set ISO 400. In a dark location where flash cannot be used, try ISO 1600 and ISO 3200; one of them should provide a shutter speed of 1/30 sec. or faster. Brace your elbows or the camera against a solid object for extra support, and activate the Image Stabilizer or Vibration Reduction system. Take three shots in quick succession; at least one of the pics should be sharp, without blurring.
Especially with a moving subject, it's important to use a high ISO in low light for a fast shutter speed to prevent blurry pictures. Most recent cameras will provide decent image quality at ISO 3200, and very good at ISO 1600 (which I used for the hockey photo at the top of this story), when you use the noise reduction techniques discussed in a recent Photo Tip of the Week: Get Better Image Quality at Very High ISO Levels.
Granted, any camera produces the finest image quality at around ISO 100. Fortunately, the latest digital SLR and mirrorless Compact System Cameras provide excellent quality at ISO 400, very good at ISO 1600 and still acceptable at ISO 3200.
Photographers who often use Macro lenses of a single focal length complain that zooms do not allow for very close focusing. That's true by comparison and sometimes you may be frustrated when you want to fill the frame with a small subject. In that case, you might want to consider a close-focusing telezoom like the Sigma 70-300mm f/4-5.6 DG OS with image stabilizer and SLD glass elements ($450). This type often has a minimum focus distance of 1.5m. That aspect, plus the ability to use a very long (300mm) telephoto focal length, will often enable you to get frame-filling shots of a large blossom, for instance.
Using a Polarizer
The vast majority of prime lenses are made so the front element does not rotate. With many of the more affordable zooms however, the front element does rotate during focusing. If you're using a polarizer, that can cause problems since the effect of the filter will change before you take the photo. I often test cameras that are provided with affordable zooms, so I have become accustomed this characteristic. The solution is simple: focus first and then rotate the filter to adjust the polarizing effect that you want for the photo.
The Bottom Line
Most of the criticism of zooms is levelled against the inexpensive 18-55mm or comparable zooms that add about $125 to the price of a camera kit. That's understandable since those are the best sellers in every category. Of course, all of the manufacturers also offer medium-priced zooms that are preferable in most aspects, as well as high-grade zooms like the Sigma 12-24mm f/4.5-5.6 DG HSM II ($1100) with one SLD and four FLD glass elements.
And the example above confirms, not all f/4.5-5.6 (and similar) zooms as "strictly for snapshooters." An increasing number of such lenses are now made with several aspherical and/or low dispersion elements for good, or very good, image quality. It's definitely worth paying a bit more for one of these, instead of getting the cheapest model of any type. Buy the best one you can afford, use it with the hints provided in the text and you should certainly be satisfied with the images that you'll be able to make.