Archived posting to the Leica Users Group, 2000/04/10
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I have been asked in private e-mails where my estimate of 9 megapixels as the digital equivalent of the 35 mm frame comes from. Here it is: In an oft quoted article "How Sharp Can You Get" published in the October 1976 issue of Modern Photography the editors used heroic measures to squeeze 100 lines/mm out of a number of high quality 35mm camera 50 mm lenses. The best performance was given by an older Leica Summicron (7 element) which reached 105 l/mm on High Contrast Copy film. Most lenses, including the Summicron reached 96 l/mm on Tech Pan. Faster films scored lower. Images on Kodachrome II peaked at 80 to 86 l/mm. To stay on the conservative side, I estimated the maximum usable resolution as 100 l/mm, fully realizing that most lens-film combinations would be less. The area of the 35mm frame is 864 sq. mm. Each sq. mm at 100 l/mm resolution requires 10,000 pixels, the total being 8,640,000 pixels. Hence the 9 megapixel estimate as the digital equavalent of 35 mm. Using 24 bit color information, this works out to a file size of about 26 MB. Moderate JPEG compression at 1:4 will reduce this to a more manageable 6.5 MB file size. While this is a reasonable approximation of the amount of information stored on a 35 mm frame using today's methods, it is far lower than the maximum that could be stored given advances in lens/film technology. The theoretical resolution of an f2.0 lens is 882 l/mm in green light. This works out to 672 megapixels and a file size of over 2 billion MB. Don't hold your breath waiting for Leica to offer lenses of this quality soon, however. All of the twentieth century efforts in camera lens design have only improved resolution for normal lenses by a factor of two. The LUG tends to place undue emphasis on resolution as the essential quality of imaging. In my youth, I worked for a Boston newspaper that never used finer than a 65 line halftone screen in its daily edition. We photographed sporting events with 4x5" Speed Graphics, not because of the high picture quality available from the large negative but pecause it could be fully processed in two minutes in concentrated developer and fixer and a printing plate could be made while the negative was still dripping wet. The paper was proud of the fact that it often had a paper on the streets showing the winning goal in a Celtics game before the crowd filed out of the Boston Arena. Today most of us watch hours of television whose images are formed by fewer than 0.3 megapixels or stare at computer screens which deliver their images at about 0.5 megapixels. A cheap low end digital camera can meet those requirements with ease. The vast majority of the world's pictures are never enlarged to a size greater than 4x6". A 1.5 megapixel camera and a basic ink jet printer will suffice. Timeliness, availability, flexibility and cost per image are often more important than resolution and tonal depth. A picture in the hand or on a electronic display screen is worth more than a dozen much finer images on a roll waiting to be developed. LarryZ