Archived posting to the Leica Users Group, 2015/11/03
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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. Happy to be educated. ---------- Forwarded message ---------- From: Doug Herr <wildlightphoto at earthlink.net> To: Leica Users Group <lug at leica-users.org> Cc: Date: Tue, 3 Nov 2015 01:14:25 -0800 (GMT-08:00) Subject: Re: [Leica] The SL Richard Man wrote: > >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. Doug Herr Birdman of Sacramento http://www.wildlightphoto.com http://doug-herr.fineartamerica.com Cheers Geoff http://www.pbase.com/hoppyman