The zoom range is limited by manufacturing limitations. The ideal of a large maximum aperture lens that zooms from extreme wide angle to extreme telephoto is not achievable. There is no big fundamental difference between a lens used for a standing camera, a video camera, a telescope, a microscope or other devices, but the details of design and construction are different. Many will say that focal length also determines the perspective of an image, but strictly speaking, the perspective only changes with one's own position relative to its subject. Perspective control can be a powerful compositional tool in photography and often determines the choice in focal length (if you can photograph from any position). In general, if you own a Canon or Nikon camera, the best lenses are those made by these manufacturers, but there are also some excellent third-party brands such as Tamron, Sigma, and Tokina, which are usually cheaper. The geometry is almost the same as with a simple perforated lens, but instead of being illuminated by individual beams of light, each image point is illuminated by a focused “pencil” of light rays. Therefore, a larger zoom designation does not necessarily mean that the image can be enlarged (since this zoom can only have a wider angle of view if it is completely reduced). The focal length of a lens is defined as the distance between the optical center of the lens and the image sensor (or film plane) of the camera when it is focused on infinity. These include inclination and shift lenses for perspective control, soft focus lenses for portrait photography, and infrared lenses for detecting light outside the normal spectrum. A standard 50mm camera lens does not significantly increase or decrease the image, making it ideal for shooting objects that are not particularly close or far away. When a zoom lens requires only a small fraction of the focal length range, a Prime lens with a similar focal length becomes significantly smaller and lighter. However, if images are taken from the same distance and enlarged and cropped to contain the same view, the images have the same perspective. If you can not find a suitable lens that is within your budget, then resist the temptation to buy something cheaper, but that does not quite what you want. A long focus lens with a small aperture can be built very easily to achieve comparable image quality: one doublet (two elements) is often enough. Zoom Some lenses, called zoom lenses, have a focal length, which varies when internal elements are moved, usually by rotating the barrel or pressing through a button that activates an electric motor. A wide aperture also allows you to use a faster shutter speed, which is important when shooting fast-moving subjects or holding the camera. If you try to fill the frame with the same subjects with both a wide-angle lens and a telephoto lens, the perspective actually changes because you are forced to move closer or further away from your subject. If you still use only the lens that came with your camera and want to improve your photography, it may be time to figure out what other lenses can do for you. The introduction of optical coatings many years ago and advances in coating technology over the years have led to significant improvements, and modern, high-quality zoom lenses give images of quite acceptable contrast, although zoom lenses with many elements transmit less light than lenses with less elements (all other factors such as aperture, focal length and coatings the same). Note: The position at which light beams intersect is not necessarily equal to the focal length as shown above, but is roughly proportional to this distance. A kit lens is ideal for getting a grip on your camera and finding out what focal lengths you like to use, but you should consider replacing it if your budget allows. The maximum usable aperture of a lens is given as the focal length or f-number, defined as the focal length of the lens divided by the effective aperture (or input pupil), a dimensionless number. Part of the photographer's creativity is to select the right lens to capture the vision of the world as it sees or wants to present it. While, in principle, a simple convex lin.