Archived posting to the Leica Users Group, 2001/10/01
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]It is not inherent to rangefinders but inherent to the M-series design, which assumes a large, heavy, springloaded cloth curtain that moves across the film plane from left to right. The maximum (let's call it) crossing speed - the speed at which the shutter can be completely open - is 1/55 of a second. All faster speeds have slits that travel across the film plane. There are only two ways to increase the speed from 1/1000 sec. One is to make the springs tighter - but spring tension won't reliably pull the M-shutter faster than 1/800 or 1/900 sec. The other is to change the slit width, but when the slit sizes get small, it is hard to control error. The fastest horizontal shutters (the Nikon titanium foil version) hit about 1/2000 sec and 1/90 synch. More modern multibladed metal and composite shutters (vertical travel) have much higher crossing speeds (1/125 and 1/250 sec). This translates into higher flash synch speeds. It also means that errors in slit width are minimized, because the necessary slit is now 2-4x the size, meaning an error of a fraction of a mm is not nearly as significant. They are also timed by oscillators, which eliminates the timing reliability of springs. Vertical travel (across 24mm and not 36mm) also helps significantly. It is surprising that Leitz never developed a new shutter that could allow their lenses to be shot wide open or at the optimum aperture in bright sunlight. With 100-speed film, the Sunny-16 rule (and modern film speed measurement), you need faster than 1/1000 sec to shoot a 35/2 Summicron at its optimum of between f/4 and f/5.6. (Same goes for Elmarits, Sonnars, Jupiters, Nikkors and any other lens with this optimum setting). To shoot a Summilux wide-open you need 1/16000 sec... I wonder how much the 1/1000 sec limitation has informed Leica rangefinder lens design. Of course the disclaimer is that film speeds were much lower (Tri-X, at 200, was "fast") back in the 1950s, when the modern M shutter was designed. But it has less of a place now, where the distinctive fingerprints of some famous of Leica lenses (Summilux 75, Noctilux, etc) are lost by f/2.8. None of this is an issue on the R, which now has a fast metal shutter. On Mon, 1 Oct 2001, Wang, Albert wrote: > Hi everyone, > > This is hopefully a straightforward question I've decided to propose. Why is > the lowest shutter speed on a Leica M6 1/1000? Could it be possible to have > a 1/8000 shutter speed on a rangefinder because I note that the Leica R8 has > that option? > > I was wondering whether it was the inherent limitations of a rangefinder > which causes Leica to design their M series (at least from M4 to M6) at the > lowest shutter speed of 1/1000 rather than jacking it downward. :) > > sincerely, > Alfie > DISCLAIMER > -- > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html > - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html