Archived posting to the Leica Users Group, 2015/11/03

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Subject: [Leica] The SL
From: wildlightphoto at (Doug Herr)
Date: Tue, 3 Nov 2015 18:47:00 -0800 (GMT-08:00)

My desire for automatic aperture is to combine the maximum aperture's rapid 
fall-off of optimum focus with the smaller working aperture's greater DOF, 
without having to turn a ring or push a button or repeat a Barnackian chant 
to cause the lens to stop down.

Doug Herr
Birdman of Sacramento

-----Original Message-----
>From: Geoff Hopkinson <hopsternew at>
>Sent: Nov 3, 2015 6:38 PM
>To: Leica Users Group <lug at>
>Subject: Re: [Leica] The SL
>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
>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>
>To: Leica Users Group <lug at>
>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
>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
>Leica Users Group.
>See for more information

Replies: Reply from mark at (Mark Rabiner) ([Leica] The SL)