Zoom lenses are designed to cover a range of focal lengths.
As good as your 35mm film or digital single lens reflex camera may be, before the image ever reaches the film or digital sensor it has to pass through a lens. When you are shopping for a zoom lens there are few key things you should consider.
Speed
Zoom lenses have different maximum apertures. The lower the number, the larger the aperture, or hole, that allows the light to travel through the lens onto the film plane. More light coming through the lens means you can use a faster shutter speed when shooting a scene, versus a lens with a smaller maximum aperture. Fast lenses are ideal for sports or low-light shooting. While zoom lenses will never be as fast as prime (non-zoom) lenses, you can buy zoom lenses with apertures as fast as f2.8.
Focal Length
Focal length refers to the distance the zoom lens will cover. There are wide angle zoom lenses with focal lengths from 10 to 24mm, standard zoom lenses that cover a 24 to 70mm focal range and telephoto zoom lenses that cover 70 to 200mm or more focal lengths. There are also zoom lenses that cover a wide range, like the Canon 28-300mm IS zoom lens. This lens is ideal if you want to buy one lens and have it cover most of the focal lengths you will be shooting.
Image Stabilization and Third Party Lenses
Image stabilization or vibration reduction are features on lenses that help reduce the impact of camera shake on your photos, while shooting at slower speeds or longer focal lengths -- if you are not using a tripod. This feature is very useful, but also adds to the price of the lens. Third party lenses, manufactured by companies like Sigma and Tamron, have improved in quality since they were first introduced. While these lenses cost less than original equipment lenses, they may support all the features of your camera. Nikon has a series of lenses that transmit the focusing data to the camera's internal metering system. In turn, that helps determine the amount of power your flash needs. Third party lenses do not support those types of features.
Shop Around
Photo retailers often display models they are looking to sell at a discount when an updated version of a particular lens is released. You can also ask if your local retailer has a layaway plan that will allow you to pay for a lens over a few weeks or months.
Consider Used Lenses
While lenses are updated from time to time, if a lens is well maintained and looked after it can last for many years. Consult with a sales associate at the camera store you frequent and let him know what type of lens you are looking for. He may be able to find you a used lens, and it may include a short-term warranty. If the store does not have a lens you want, ask if they know of anyone who is considering selling one. You can also check on-line auction sites.
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