Archived posting to the Leica Users Group, 2015/11/04
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]All true , but nothing trumps the sccuracy of a fully wide open aperture Frank Filippone > On Nov 4, 2015, at 10:22 PM, Geoff Hopkinson <hopsternew at gmail.com> > wrote: > > Yep didn't forget that. I was attempting to explain that if the lens was > already at the shooting aperture (like an M lens for example) it may be > that an EVF can still display a bright enough image for focussing (that is > your EVF brightness is controllable). > Focus at the shooting aperture of course defeats any focus shift (for > example from f/1.4 to f/4). Much depends on what you are shooting I > imagine. > Just played with this on the XT1 and the Summilux 50 ASPH down to f/8. > > However personally I have never found DoF preview sufficiently precise or > particularly useful in any camera at all from the 70's forward. I may be an > outlier there ;-) > > > ---------- Forwarded message ---------- > From: Frank Filippone <red735i at verizon.net> > To: "'Leica Users Group'" <lug at leica-users.org> > Cc: > Date: Tue, 03 Nov 2015 22:35:51 -0800 > Subject: r > Yes, all true.....but you forget that DOF is, for example at F8, greater > than at F2. So focusing is much less precise without auto stop > down.......... > > Frank Filippone > Red735i at verizon.net > > > Do I have it right that the desire for automatic diaphragm control is for > focus at maximum aperture then stopping down to shooting aperture at the > moment of exposure? > > Doesn't the use of the EVF potentially permit the finder brightness to be > controlled? If the lens is stopped down (ie not operating with auto > diaphragm) of cause the image arriving at the sensor is what is used for > focussing. So the desire for auto diaphragm control comes from the OVF > systems? > > M lenses of course are already being employed with the initial SL units in > the field. >> >> You can get autoexposure only if the camera knows what the open >> aperture and the taking aperture are. If the lens does not generate >> those info, then some kind of manual system is needed > > Autoexposure with TTL metering in apertured-preferred mode is simple with > no > auto-diaphragm, no data other than light, ISO and shutter speed is needed. > > With TTL metering and an automatic diaphragm the camera needs to know the > difference between open aperture and working aperture. It does not need to > know what the actual open aperture is or the actual working aperture, only > the difference. Any other data is extra and can be used for the user's > convenience, but is not required for autoexposure function. > > > Cheers > Geoff > http://www.pbase.com/hoppyman > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information