What kind of lens do you need?
Your digital camera photographic needs determine the kind of lens you need. There are many types of lenses and each is suitable to achieve certain results. To understand which lens is needed for your digital camera, a basic understanding of the lens is required.
What is a lens?
A lens is the eye of your digital camera. It captures the light as it comes from the shutter and then after necessary refraction, sends it to the image sensor where the image is recorded. Lenses are comprised of several "lens elements". The purpose of each of these lens elements is to direct the path of light rays in such a manner that the recreation of the image is done as accurately as possible on the digital sensor. The aim of the lenses is to minimize the aberrations, while utilizing the least expensive and the fewest of elements. The quality of the lenses determines artifacts like image blurring, misalignment of colors (chromatic aberration), reduced contrast, radially decreasing image brightness (vignetting) and distortion. These artifacts are present in all lenses to varying degrees. There is no lens yet made which can be termed as aberration free perfect lens. Lenses are manufactured from glass and plastic. Glass lenses are superior and more expensive.
Lenses are listed in terms of aperture range (f-numbers)
The aperture range of a lens refers to the amount that the lens can open up (let more light in) or close down (let less light in). Lens apertures are listed in terms of f-numbers. Larger f-numbers have smaller aperture openings and smaller f-numbers have larger aperture openings. Lenses with larger apertures are faster because the shutter speed can be adjusted accordingly. A smaller aperture means that the object remains in focus over a wider range of distance (known as depth of field). When you buy a lens, see the specifications carefully. Usually maximum apertures are listed. In terms of depth of field and exposure, wider ranges of aperture settings provide more artistic flexibility. The maximum aperture specification is important and is generally listed along with the focal length, for example, f/X or f:X. Lenses with larger maximum apertures are usually much heavier, larger and more expensive. For hiking, travel, or wildlife photography, size and weight of the lenses become critical since they have to be carried over long periods in unsuitable terrains.
Two basic kinds of lenses
There are two basic kinds of lenses, namely, fixed or prime lenses and zoom lenses. With a zoom lens, you can alter the focal length within a pre-defined range. A prime or fixed focal length lens is where you cannot alter the focal length. A zoom lens is generally used of dynamic subject matter, such as in photojournalism and children's photography. With a zoom lens, change of perspective and a change of composition can be achieved without any physical dislocation of the photographer. The primary advantage of the prime lens is the cost, weight and speed. In the hands of an experienced photographer, an inexpensive prime lens can generally provide as good a result as a high-end zoom lens would do.
Different lenses for different uses
There are many types of lenses designed for different purposes. For architectural photography, generally extreme wide-angle prime or zoom lenses are used. For Landscape, a wide-angle prime or zoom lenses are used. For street and documentation of general events, normal prime lens is generally used. For portraits, a medium telephoto zoom lens is generally used, and for sports, bird, and wildlife photography, a telephoto zoom lens is invariably used.