Archived posting to the Leica Users Group, 2000/05/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Art, I suspect that the reason Leica uses another lens, the Elpro, for achieving 1:2 to !.!:! magnification with the 100 APO is based on optical considerations. The 100 is an 8 element pseudo zoom lens in which the rear two elements remain stationary whereas the front 6 elements move as a unit to achieve focusing - in fact the focal length of the lens changes from 100 mm to 92 mm from the infinity to 1:2 focusing range. Perhaps the change in focal length as the lens is focused is the reason why extension tubes or optical additions behind the lens will not work. Only the Leica optical designers know the reasons why. The front Elpro is designed specifically for the 100, and Leica states that it has no practical effect on the superb performance characteristics of the lens. An advantage of this approach is that the field of view of the lens plus Elpro is narrower, and this is usually beneficial in close-up photography. In addition, no exposure compensation is necessary since there is no bellows effect. Leica did not recommend the use of any device between the 100 APO lens and camera body, not even the 2X extender. Since its advent, they do recommend the use of the APO 2X extender. This leads to another question: Can the APO 2X extender be used with the same optical performance as the 2x extender on lenses which do not have internal focusing? Or, conversely, does the 2X extender result in acceptable performance on the internal focusing APO lenses? My suspicion is that the APO 2X extender, and the APO 1.4X extender, are designed for the internal focusing APO lenses, and the 2X extender is designed for the non APO lenses (except for the 180 APO f3.4 Telyt) which use the bellows effect for focusing. Anyone know whether this is true? I don't have any of the extenders, and, therefore, have no practical experience to draw on. The above is Leica's approach, but the Vivitar 100 f2.5 macro lens, vintage of about 30 years ago, was also a pseudo zoom lens with stationary rear elements, but this lens used an approach in which an optical unit was inserted between the lens and camera body to achieve 1:2 to 1:1 magnification. Like Leica, Vivitar used an optical approach to achieve higher magnification. The Leica approach has the advantage that the optical unit is added to the front of the lens, which does not require the lens to be removed from the camera body. By the way, the Vivitar lens was tested by Modern Photography, and displayed superb resolution, probably the best of its day. I wonder if this design was the inspiration for the Leica 100 APO? Ferrel Anderson