Archived posting to the Leica Users Group, 2000/05/23
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]"Sal DiMarco,Jr." <sdmp007@pressroom.com> wrote: >As to your second question... Look at a projector lens, is doesn't require a focusing mount, a diaphragm or any of the real fine machining a camera or enlarger lens does. This is enough to seriously reduce production costs. Plus, if you talk to a lens designer, they can give a lot more reasons why projector lenses are easier to make than camera lenses. I'd love to hear a lens designer explain what those "lot more reasons" allegedly are. Lens design is a matter of controlling rays of light, and the processes of dispersion and refraction work exactly the same way irrespective of whether the light is proceeding from the outside world and onto the film, or from the film to the outside world. So unless there is something I'm not grasping, a good projector lens should make a good camera lens and vice versa. However, the 125mm f2.5 Hektor for the Visoflex (which is optically identical to its projector lens counterpart) has a degree of softness. It's always puzzled me that while we take the picture with (for example) a double-Gauss configuration lens such as a 50mm Summicron whose individual elements are accurately set up in a metal mounting, we often trust the job of projecting the result to a relatively simple (triplet?) lens whose elements are in a plastic mount. (Do you remember the bit during the factory tour last year when our guide explained why plastic was not good enough to accurately hold the elements of a Leica lens?) I suspect that there is an element of "good enough" in projector lens design. The typical design has an aperture of around f2.5 and a focal length of 85mm. Now when Zeiss designed their 85mm f2 lens for the Contax during the 1930s, they decided to adopt the classic Sonnar layout, while the simpler triplet construction was reserved for the f4 Triotar of the same focal length - a lens which as been described as a "rather average item". By 1990 four glasses could make up a top-class 90mm f2.8 lens, but what has probably happened in the world of projection lens design is that the lower-performance classic triplet configurations have become seen as adequate for the ephemeral task of projecting an image. And some of the resulting lenses are pretty poor. The Hektor lens on my relatively-new P150 is comfortably outperformed by the Elmaron of a 1970s Pradolux which I bought very cheaply at this year's Leica Historica swap meet in Germany. If I ever find a Colorplan which will fit the Pradolux, I'll be buying it. Regards, Doug Richardson