“Tele” comes from Greek and has the meaning of “far.” Telephoto lenses enable the photographer to photograph objects “up-close” from a far distance. A telephoto lens essentially functions the same way a telescope does.
In comparison with normal lenses, telephoto lenses have a higher focal length. A lens is considered to be a telephoto lens if it has a focal length of between 70 and 500mm. The larger the focal length of a lens is, the larger the lens can enlarge the object being photographed. It should be noted that with the enlargement of the object in the photo always comes a reduction in the overall image detail.
Telephoto lenses with a focal length between 100 and 300mm are retrofocus lenses most of the time. Thanks to their design, where the image-side of the main plane is located in front of the lenses, a reduction of length of up to 30% is achieved. Thus, many telephoto lenses have a shorter focal length.
Lenses with a slight tele-focal length between 70 and 135mm are referred to as portrait lenses. A lens with a tele-focal length of 135 to 200mm is considered to be a standard telephoto lens. Lenses with a focal length of 200mm or more are called super telephoto lenses.
Pictures that are shot with a telephoto lens have a significantly lessened depth of field than pictures taken with a wide-angle lens. The depth of field refers to the area of the photo that appears sharp and this is influenced by both the aperture and focal length of a lens. Lenses with a lower tele-focal length (up to about 135mm) are often used in portrait photography. The shallow depth of field focuses on the face of the person being photographed and accentuates it.
Standard telephoto lenses with a focal length of up to 200mm are mainly used in nature and travel photography. Super telephoto lenses, on the other hand, are preferably used in sports and animal photography. Comparatively cheap super telephoto lenses often have a very low degree of light intensity, so they are not suitable for photographing in poor lighting conditions. If you want to take sharp photos in twilight using a super telephoto lens, expect to pay a pretty penny for a telephoto lens capable of capturing such photos.
In order to take images that don’t appear blurry, the golden rule is that the shutter speed used should correspond to the reciprocal of the focal length. For example, with a focal length of 200mm, the shutter speed should be 1/250 seconds or shorter. With a focal length of 300mm or more, you should always use a tripod since it’s hardly possible for you to take steady pictures while holding the camera when the images are so enlarged.