Zoom lenses come in all shapes and sizes, but typically cover a certain range. There are wide angle zooms, mid-range zooms, and telephoto zooms. Camera manufacturers also produce lenses that cover a very large range of focal lengths, say 18-200mm or 28-300mm. These are large zooms meant to handle just about any situation.

The range of a zoom lens often has a direct effect on the image quality of that lens, as zoom lens design requires compromises in resolution throughout the lens's various lengths. So generally speaking, the tighter the range of the zoom, the higher quality the lens is capable of achieving. This will be specifically noticable on those 18-200mm and 28-300mm types of zoom lenses.

Zoom Lens Apertures

Cheaper zoom lenses often contain variable aperture designs. This means that your maximum aperture will change, getting smaller as you zoom in. A lens that is relatively fast at its widest length can be unbearably slow at its telephoto length (and that telephoto setting is where you will want a fast aperture). Lenses such as a 24-85mm f3.5-4.5 lens are typical of this variable aperture lenses. That lens would be have an aperture of f3.5 on the wide end (24mm) and an f4.5 aperture when zoomed in to 85mm. To compare, a prime 85mm lens would normally have an ultra-speedy aperture of f1.8, letting in substantially more light.

To get a zoom lens with a constant aperture is going to cost you more money, but can be essential— especially when you're doing a lot of available-light photography. Paying more for the fixed aperture zoom lens also often buys you a much higher quality lens. One manufacturer has a 24-85mm/f3.5-4.5 lens and a 24-70mm/f.2.8 lens. You'll pay four times the price for the fixed f2.8 lens, but the image quality will typically be much higher throughout the zoom's range.

Other Zoom Lens Options

If fast autofocus is important to you (especially if you're shooting sports and action photographs), you'll want to put any zoom lens to the test before you buy it. Some zoom lenses focus significantly faster than others, and your bargain entry to the long lens club may turn out to be a clunker.

A feature available on higher-end zoom lenses is Image Stabilization, or Vibration Reduction. These technologies help lesson the amount of camera shake when you're hand-holding a lens, and are very helpful in low-light situations. If you're shooting a lot of action it won't really help, but this feature is especially handy in low-light situations when you're without a tripod.