Archived posting to the Leica Users Group, 2002/04/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>Guy; >Very sluggish response wide open. Also, there seemed to be a great >amount of fluctuation or uncertainty. At other times all the lights >wanted to stay on. I have new batteries in it. ???? >Slobodan Dimitrov As for the sluggish response and light wanting to stay on, yes, sounds like you need new batteries. As for the fluctuation or uncertainty in the reading, that might be due to the vignetting of the lens wide open, which will also effect meter readings. I'm appending a post by John Collier and a response by Henning that discuss the way metering can be effected when using the Noctilux wide open. I'm not sure if this will help, but it sure cleared up some questions I had about the issue. Good luck and let us know how this gets resolved. Guy * At 12:00 PM -0700 11/15/01, John Collier wrote: >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 As John wrote, the apertures of the Noctilux and Summilux are truly f/1 and f/1.4, and if you follow the normal sequence, you will get correct exposure at f/1 and 1/1000 sec if you otherwise get correct exposure at f/2 and 1/250sec. However, this is only true at the center of the frame. The further you go to the edges, the more underexposed the shot at f/1 is relative to the shot at f/2. The metering in effect compensates slightly for this, because the falloff is strong enough to affect the total amount of light that hits the white spot (which is what gets metered) and thus the meter expects a slightly greater amount of exposure at f/1. If you check this out carefully, and do the exposure series at a constant light level, varying aperture and shutter as accurately as you can according to the meter, you will find that the center of the shots at f/1 is slightly overexposed compared with the other shots. If you check your very fast SLR lenses, especially the normal to wider ones, you will find the same metering anomaly. This applies to full area, centerweighted and matrix metering; not spot except in certain cases where off-center spot metering is possible like on recent Canons. If your camera does not seem to do this, the area you are trying to meter is maybe such that f/1.4 at whatever would actually give you a slightly overexposed (by 1/6 stop or less) shot, while f/1 at the next higher speed would then want to meter just at the lower edge of the meter's agreement. In practice, this is all nothing to worry about. Just match the little lights as you normally do, and shoot. True, at f/1 the meter will ask for slight overexposure, but human tendency is to kind of push things at lower light levels, and this compensates a little bit for that, and besides, if you look at metering accuracy graphs, you'll see that most exposure meters are not dead on the whole way across the aperture range, and tend to underexpose slightly on the darker end, which also compensates for the effects noted. Lastly, this whole exposure thing is not as much of a science as is sometimes made out (unless you are mainly shooting completely evenly lit brick walls) and bracketing can be useful if greater accuracy is required. Film can be off 1/3stop as well as processing, and these factors are often greater than any metering discrepancy. The best way to handle this is to practice with the film and processing of your choice, in conditions that you normally shoot, and meter accordingly. - -- * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@archiphoto.com |[ ]| http://www.archiphoto.com - -- 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