Archived posting to the Leica Users Group, 2001/11/15
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]It is not that the Noctilux and Summilux are not true f/1 or f/1.4 lenses but that, under certain lighting conditions, the inherent wide-open vignetting will affect the metering area and you will not get a strictly geometrical shutter/aperture relationship happening. The meter is not being fooled if you do not follow it, it will underexpose. I have dug up the scans from the last time this came up and if someone would like them, just let me know. John Collier > From: Nathan Wajsman <wajsman@webshuttle.ch> > > I had not noticed it in Osterloh's book before, but I now looked it up (p. 43, > German edition) and sure enough, he says that, in effect, the actual maximum > aperture of a Noctilux is not f1 but somewhere around f1.1-f1.2. I do not own > one of those beasts anymore, but when I did, I never noticed the effect, and I > cannot produce it with my Summilux. perhaps Ray should have his camera/lens > combo checked after all. > > Nathan > > John Collier wrote: > >> It is normal. The inherent vignetting of any optical system wide open causes >> this effect. It is most noticeable with the Noctilux. See Osterloh's Leica M >> book for a well illustrated explanation. >> >> John Collier >> >> PS: Try your local library for the book. I might be persuaded to scan the >> relevant sections out of my copy if you cannot locate it. >> >>> From: Ray Moth <ray_moth@yahoo.com> >>> >>> I've just noticed a peculiarity in the behaviour of the light meter in >>> my M6 TTL, using a 50mm Summilux-M lens. If I adjust the aperture from >>> f/1.4 to f/2 or vice versa, the meter doesn't register any change, >>> whereas a change in shutter speed does register. >>> >>> For example, if the meter indicates that f/1.4 at 1/500 sec. will give >>> the correct exposure, then I would expect f/2 at 1/250 sec. would give >>> the same indication but it doesn't; it shows over-exposure, as if I'd >>> selected the slower shutter speed but left the lens aperture at f/1.4. >>> Conversely, if I started at f/2 and 1/250, a change to f/1.4 and 1/500 >>> would indicate an under-exposure. The lens aperture selector seems to >>> function properly. Has anyone else experienced this problem? >>> - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html