Nikon D7000 manual 361

Chapter 11 ■ Working with Lenses 361

When selecting between zoom and prime lenses, there are several considerations to pon- der. Here’s a checklist of the most important factors. I already mentioned image qual- ity and maximum aperture earlier, but those aspects take on additional meaning when comparing zooms and primes.

■Logistics. As prime lenses offer just a single focal length, you’ll need more of them to encompass the full range offered by a single zoom. More lenses mean additional slots in your camera bag, and extra weight to carry. Just within Nikon’s line alone you can choose from a good selection of general purpose prime lenses in 28mm, 35mm, 50mm, 85mm, 100mm, 135mm, and 200mm focal lengths, all of which are overlapped by the 28-200mm zoom I mentioned earlier. Even so, you might be willing to carry an extra prime lens or two in order to gain the speed or image qual- ity. The relatively new Nikkor 35mm f/1.8 DX lens offers a fast “normal” focal length for those owning APS-C cameras at an economical price.

■Image quality. Prime lenses usually produce better image quality at their focal length than even the most sophisticated zoom lenses at the same magnification. Zoom lenses, with their shifting elements and f/stops that can vary from zoom posi- tion to zoom position, are in general more complex to design than fixed focal length lenses. That’s not to say that the very best prime lenses can’t be complicated as well. However, the exotic designs, aspheric elements, and low-dispersion glass can be applied to improving the quality of the lens, rather than wasting a lot of it on com- pensating for problems caused by the zoom process itself.

■Maximum aperture. Because of the same design constraints, zoom lenses usually have smaller maximum apertures than prime lenses, and the most affordable zooms have a lens opening that grows effectively smaller as you zoom in. The difference in lens speed verges on the ridiculous at some focal lengths. For example, an 18mm- 55mm basic zoom gives you a 55mm f/5.6 lens when zoomed all the way out, while prime lenses in that focal length commonly have f/1.8 or faster maximum aper- tures. Indeed, the fastest f/2, f/1.8, f/1.4, and f/1.2 lenses are all primes, and if you require speed, a fixed focal length lens is what you should rely on. Figure 11.9 shows an image taken with a Nikon 85mm f /1.4 lens in low-light conditions.

■Speed. Using prime lenses takes time and slows you down. It takes a few seconds to remove your current lens and mount a new one, and the more often you need to do that, the more time is wasted. If you choose not to swap lenses, when using a fixed focal length lens you’ll still have to move closer or farther away from your subject to get the field of view you want. A zoom lens allows you to change mag- nifications and focal lengths with the twist of a ring and generally saves a great deal of time.