Many types of construction have been adopted in photographic lenses since the invention of photography in 1839, but very few of these have survived to the present day. The simpler types generally work at low relative apertures, but the supposed rule that a high aperture and a wide angular field are incompatible no longer holds. A few special lenses have been made with an aperture greater than this, but they mostly cover only a very narrow field.
At one time, not too long ago, photographers were very much aware of the type and kind of lens they were using on their cameras, and it was a matter of pride to own a Rapid Rectilinear or some type of anastigmat. Gradually, however, knowledge of lens structure has become less important, and today most photographers have absolutely no idea of or interest in the structure of their lenses. So long as the lens has the desired focal length and aperture, is priced within their means, and gives good definition with adequate depth of field, most photographers are satisfied. This is not a unique phenomenon, as most people have no knowledge of the working of their refrigerators, calculators, typewriters, or of many other appliances in everyday use. However, there are some who are interested in lenses, and it is hoped that this chapter will give them some useful information.
The camera manufacturer, of course, is vitally concerned with lens structure, and endeavors to obtain the best possible image quality at the lowest cost. Modern methods of lens design and manufacture are of the greatest importance to the entire camera industry.
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