There are three basic types of lenses: standard, wide-angle and telephoto. A normal lens will take the picture almost exactly as to how you see the scene. 50mm focal length (the distance between the lens and what you are photographing) is the most typical type of lens and the most popular. Overall, the shorter the focal length, the more crisp the photograph. This lens is relatively light weight, and the aperture (the opening in the lens that allows light to come through) lets you to take photographs even in low light.
Wide-angle lenses are great for capturing the whole picture. If you're planning on taking landscape pictures, these will help you

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capture the entire scene. But, while they do help you capture the entire scene, you want to be able to zoom in as close as you can to get a great picture. These lenses are perfect for landscape photography and group/wedding photography. The 24mm and 35 mm are the most popular focal lengths for this type of lens.
A telephoto lens is a necessity because it brings your subject to you. While everybody loves being in on the action, sometimes the action is too far away. For example, if you plan on taking animal pictures, you can't be standing over the lion as it attacks the wildebeast. You're going to have to be able to zoom in and get a great shot. These lenses are also very popular with sports photographers. This is where the telephoto lens comes into play. The s 70mm and 300mm focal lengths are the most popular telephoto lenses.
These lenses don't have to be particularly fast if you are just starting out. A fast lens lets in light a lot quicker. This means a faster shutter speed and the ability to hand hold a camera in lower light situations. If you're just beginning, you're probably going to be taking it slow anyway so you don't need your lens to be that quick. Plus, the faster the lens the more expensive that it's going to be. Stick with something simple.