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Increasing the bending angle has an obvious effect. Light beams from a particular point will converge at a point closer to the lens. In a lens with a flatter shape, light beams will not turn as sharply. Consequently, the light beams will converge farther away from the lens. To put it another way, the focused real image forms farther away from the lens when the lens has a flatter surface.
Increasing the distance between the lens and the real image actually increases the total size of the real image. If you think about it, this makes perfect sense. Think of a projector: As you move the projector farther away from the screen, the image becomes larger. To put it simply, the light beams keep spreading apart as they travel toward the screen.
The same basic thing happens in a camera, as the distance between the lens and the real image increases, the light beams spread out more, forming a larger real image. But the size of the film stays constant. When you attach a very flat lens, it projects a large real image but the film is only exposed to the middle part of it. Basically, the lens zeroes in on the middle of the frame, magnifying a small section of the scene in front of you. A rounder lens produces a smaller real image, so the film surface sees a much wider area of the scene (at reduced magnification).
Professional cameras let you attach different lenses so you can see the scene at various magnifications. The magnification power of a lens is described by its focal length. In cameras, the focal length is defined as the distance between the lens and the real image of an object in the far distance (the moon for example). A higher focal length number indicates a greater image magnification.
Different lenses are suited to different situations. If you're taking a picture of a mountain range, you might want to use a telephoto lens, a lens with an especially long focal length. This lens lets you zero in on specific elements in the distance, so you can create tighter compositions.
If you're taking a close-up portrait, you might use a wide-angle lens. This lens has a much shorter focal length, so it shrinks the scene in front of you. The entire face is exposed to the film even if the subject is only a foot away from the camera. A standard 50 mm camera lens doesn't significantly magnify or shrink the image, making it ideal for shooting objects that aren't especially close or far away.
The quality of any image, whether made by a digital or an analogue camera, can only ever be as good as the lens that is capturing the light and bending it back towards the light receptor (CCD or film). Often, the biggest single difference between a professional camera and a cheaper alternative is simply the quality of the lens that is used on the front of the camera. However, for the digital camera, the need for high quality optics is even more important.
Although some scanning-backs (using a tri-linear array) can provide a larger capture area, most of the matrix cameras tend to have receptors considerably smaller than a 35mm analogue camera, which means that is imperative that the lens is able to accurately resolve very fine detail within this small area. So far, very few digital cameras have been produced with a receptor using the full size of 35mm film.
This is seen as somewhat of a holy grail by digital photographers, as it will allow these cameras to be used with normal 35mm lenses, without having an apparent lengthening of focal length due to the smaller frame size. Although at present there are only a few cameras that have a receptor of this physical size, it is likely that there will be more shortly. At present it is only the most expensive SLR type digital cameras made by Kodak, Canon and Contax that do.
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