Archived posting to the Leica Users Group, 2000/09/14[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
Introduction and background. A few years ago in Solms, I was shown a lens, a compact 1:2.0/28mm lens for M. It was a prototype, to be sure, but it was ready for production, all optical computations and tests were done. On my question why this lens never made it to the production stage, Mr. Kölsch answered, that he expected more performance from a new lens of these specifications. So a new design was created from scratch: the Summicron-M1:2/28mm ASPH., scheduled for delivery early in 2001. The optical prescription of the lens is quite fascinating. It fits in the genealogy of the seminal Summilux ASPH, a design that decisively departs from the classical Double-Gauss formula. This design-type, now more than a 100 years old, has been stretched to the limits and a performance plateau has been reached. The new Summilux design, incorporates the negative front and back surfaces and the aspherical surface. It is probably the first lens that has been designed specifically around the use of aspherics. Retrofocus designs are a second approach to step out of the shadows of the Double-Gauss formula. More lens elements can potentially improve performance, as more parameters can be controlled. The new Summicron-M 1:2/28mm ASPH picks up design elements of both: the lens group in front of the aperture is an enhancement of the Summilux (front group) design and the lens group behind the aperture fits into the retrofocus family and is a derivative of the 2.8/28 formula. We should not press the point, however, as a lens design is a creative whole and not a mix of ready made components. The message should be that the new Summicron is based on the best design principles currently available in Solms thinking. The location of the aspherical surface is different and probably decisive for this design. The ergonomics. The new 2/28 is indeed a very compact lens, comparable to the current 2.8/28 version. Measurements are (2.8 version in parentheses): length from flange: 41mm (41.4mm), overall diameter: 53mm (53mm), front diameter: 49mm (48mm). Both lenses use filtersize E46. For a lens with twice the speed this is a remarkable feat. This design indicates the direction of future Leica M designs: compact and high speed and high performance. The somewhat weak performance of the old Summilux 1.4/35mm could be excused with reference to its compactness, which forced the designers in those days to find a compromise between size and performance. Now the circle has been squared. The lens operates very smoothly, and the aperture ring clicks with just the right amount of resistance and fluidity. When taking pictures with the new Summicron 28, I was amazed how quickly I could focus with the focusing tab and I have to confess that I hardly missed a shot, when focusing moving objects. The depth of field with a 28mm lens, even at an aperture of 1:2 exceeds of course the DoF of the Summicron 50 by a factor of 2, which brings real advantages in street shooting.