Lenses, and lens quality, are of major concern to a photographer. Lenses were originally ground by hand. Today, lenses are machine ground and computer-designed.
The simplest way to form an image is by using a pinhole. This will form an image, but to get a sharper image, you need to use a smaller pinhole, which (greatly) increases exposure time. Pinholes are also subject to diffraction, or a bending of light, around the edges.
Contemporary lenses are invariably of the compound type. That is, they are made with multiple lens elements, combining to correct image aberrations.
The number of these elements, along with their inherent material quality (the quality of the glass) serve to create the quality of image. More elements mean that separate lenses are doing their own job, rather than combining multiple tasks into one piece of glass. Better glass simply means the glass is more optically pure, and does not introduce its own aberrations.
There are several different shapes of lenses, or elements. Without going into the physics used for each, the main shapes are: Plano convex, plano concave, converging meniscus, and diverging meniscus.
The biggest difference in lenses is their focal length. The focal length is measured from the center of the lens to the film, or the focus point, where the lens focuses light. A shorter focal length bends light at a sharper angle. Simply looking at the difference in the shape of the outer element of a 28mm lens compared to a 50mm lens will show the 28mm being more rounded:
Short lens (left) vs. longer lens.
Focal length determines both the magnification of and image, as well as the angle of view. Angle of view is the width of the image. A ‘normal’ lens is called normal because it best approximates human vision—both magnification and angle of view—for a particular film format. A short lens (shorter focal length than normal) will have an extended angle of view, but lower magnification, while a long lens will have the opposite, a compressed angle of view with a higher magnification.
Lenses are divided into types, by focal length. These types—normal, short, and long, are based on camera format, so the same length lens may be long for a 35mm camera, but normal for medium format. The focal lengths discussed below are for 35mm format.
|Normal Lenses||For 35mm format the standard normal lens is 50mm in focal length. The term ‘normal’ derives from the approximation of our vision. The angle of view of a 50mm lens is about 60º, close to our own (human) visions.|
|Short Lenses||Short, or wide angle lenses, are anything shorter than 50mm, for 35mm format. Common focal lengths are 35mm and 28mm. Short lenses are available down to 14mm, referred to as a fisheye.|
|Long Lenses||Long, or telephoto lenses, are (correspondingly) any lens with a focal length greater than normal, which is greater than 50mm for 35mm format. Common lengths are 85mm and 105mm. Much longer telephotos are available (600mm +), usually used by wildlife and sports photographers.|
Zoom, or multi-focal-length lenses, come ain a wide variety of sizes. Some standards are 28-80mm and 70-200mm, with many shorter, longer, and in-between. Zooms are a good compromise when more than a fixed standard lens is needed. Having the two sizes above pretty much covers most needs.
|Macro/Micro||Macro and micro lenses are lenses which have additional elements which allow closer focusing.|
A camera that captures the photo not on film,
The following are my Classic Nikon F2 AS and F3 Cameras and lens :
A camera that captures the photo not on film, but in an electronic imaging sensor that takes the place of film. The following is my Canon Power Shot Pro 1 digital camera.