Know what type of lens you want for your camera.
Whether you are an amateur or a professional photographer, the quality of photos you are able to produce depends upon the quality and features of the lens you use. Shopping for lenses can be confusing since they have several technical components. With a little understanding about the features available, however, you can select a lens easily if you know what types of pictures you want to take and within a certain price range.
Focal Length
Lens focal length is the distance from the front of the lens to the surface of the film or digital sensor. Within this length there are the optics that redirect light rays to reproduce an image as accurately as possible. A short focal length makes a wide-angle lens; it is best for photographing landscapes and architecture. Lenses with focal lengths below 35 mm are considered wide-angle. One benefit of a wide-angle lens is that you do not have to hold perfectly still to avoid distortion if you are taking a handheld shot. Longer focal lengths make telephoto lenses; these are best for capturing portraits, sports and wildlife. Lenses with focal lengths above 70 mm are considered telephoto. The longer the focal length, the steadier the camera must be for a clear picture. Photographers with telephoto lenses often use tripods to stabilize their shots. Standard lenses have focal lengths between 35 mm and 70 mm; these can be good for portraits and documentary shots.
Zoom
Lenses are either "zoom lenses" or "prime lenses." A zoom lens has an adjustable focal length, while a prime lens has a set focal length. The benefit of a zoom lens is that you can take a wider variety of shots. The downside is that images can become easily distorted, the lens itself can be bulkier and it is more expensive than a prime lens. Different types of zooms will provide various ranges of focal lengths. Note that a true zoom lens adjusts the focal length; some digital cameras simply magnify an image, a process that is not the same because it reduces image clarity. While many people prefer zoom lenses because of their versatility, prime lenses with set focal lengths can be useful if you specialize in a particular type of photography. They tend to be less expensive for the quality of photos they produce.
Aperture
Lens aperture describes how much a lens opens up to let in light. It is often measured by an "f-number." F-numbers are written as fractions with an "f" over a number, such as f/1. The larger the denominator, the smaller the area that lets in light. An aperture of f/1 has a large light-gathering area, while an aperture of f/16 has a small light-gathering area. All lenses can be set to a small aperture, but they each have different maximum apertures. Note that maximum aperture can vary if you have a zoom lens. There are three benefits to having a large maximum aperture. First, since you let in more light, you can take more photos in a natural light setting. Second, you can use a faster shutter speed to capture more action shots. Finally, you can reduce the depth of the field of your shot, which means that you can focus on objects in the foreground while blurring objects in the background. This reduces the impact of a busy background. The only drawback to a high maximum apertures is that it can be expensive.
Single Lens Reflex (SLR)
SLR technology uses mirrors to reflect the image in the lens to the viewfinder. It is becoming less common with the development of low-cost digital cameras with preview screens that project the image captured on the image sensor. Many professional photographers still prefer SLR to digital projections, however, because SLR cameras have interchangeable lenses and have less shutter lag, enabling more precise timing in shots.
Other Features
There are several other features you can find on many lenses available on the market. Most cameras have auto-focus for the average amateur photographer. More advanced auto-focus options include silent auto-focus, which may be preferable if you dislike the sound that focusing cameras make. Full-time manual focus allows you to adjust the focus manually without switching off the auto-focus feature. Another feature is the quality of optics; special optics can reduce flare, distortion and extra light. A non-rotating front element prevents the front of the lens from rotating when you focus, which is important if you use a polarizing filter that changes light depending upon how it is oriented over the front. Crop reduction reduces the amount of an image that is cut out based on the placement of the film or sensor behind the lens. Image stabilization or vibration reduction helps you capture clear images without a tripod. Internal zoom lets you adjust focal length without adjusting the external length of the lens.
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