Archived posting to the Leica Users Group, 2001/01/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Jim Brick wrote in part: > Usually, in the world of engineering, all of the parameters are worked out > before hand. The design is done utilizing all of the parameters, such as > transmittance of the glass and coatings, and the optical formula and lens > diameters all combined, are worked out to give precisely the proper > f/stops. Therefore, an f/2.8 lens is designed to be an f/2.8 lens. And the > diaphragm is set-up to give precise f/stops from f/2.8 to whatever (f/16, > f/22, ...). The engineering is done up front. After that, it's just > manufacturing, assembly, and testing. Perhaps this is why a Leica f/2 lens > is bigger around than a brand-x f/2 lens? > Jim, I believe the larger than normal front element started by Leitz with the Summitar 50mmm f2 lens. This was done to reduce vignetting especially in colour film. You'll find, that if you measure the front element of this and later f2 lenses. they all seem have a to large diameter to give you f2. It is more like f1.5. However ,the diaphragm will take care of the correct maximum. According to Leitz, it was done first on the Summitar, because before that, they had not managed to correct certain aberrations as well. (I forget now which ones). I suppose making the front element larger at a 50mm f2 lens, does not increase the weight and size to much. However it would not be sensible to do the same with the Noctilux. Regards, Horst Schmidt.