[Leica] R lenses on any Digital body - exposure problem

[leicar at q.com (Aram Langhans)]

The same problem exists in manual metering mode, at least with my Rebel XTi.
If using manual mode, you must meter at full aperture, then, if you stop
down say 3 stops, you then must slow the shutter down the appropriate amount
and ignore what the meter is telling you.  It will show that you are
underexposing, when in reality you are properly exposing.  A real PITA, but
it works.  AE mode is easier if you use the +/- compensation and are always
going to use a particular f-stop for a series of photos.  However, if you
are stopping down many stops for DOF purposes, the manual mode might be your
only choice because the +/- 2 stop range of the Rebel in Aperture mode might
not be enough to compensate.

Aram



> From: Douglas Sharp <douglas.sharp@gmx.de>
> Subject: Re: [Leica] R lenses on any Digital body - exposure problem
> To: Leica Users Group <lug@leica-users.org>
> Message-ID: <4980DFAA.5090609@gmx.de>
> Content-Type: text/plain; charset=UTF-8; format=flowed
> 
> Hi,
> 
> although I posted this only a month or so ago, here it is again:
> 
> I never bothered to find out if it applies in manual metering mode -
> does any one know if that works correctly?
> 
> Bob Palmieri sent it to me OL in 2005
> 
> This is what Canon says about it:
> 
> The EOS 20D focusing screen is optimized for superior brightness at
> moderate apertures from about f/3.5 and smaller, compared to
> conventional ground glass designs. This makes the viewfinder image
> brighter and easier to focus at those moderate apertures, but the
> trade-off is that it passes disproportionately more light to the
> metering system. When a Canon EF lens is mounted to an EOS camera, a
> variable  exposure compensation factor (a program curve, not just a
> fixed compensation factor) for this phenomenon is fed through the
> system
> in order to provide correct metering for all apertures. However, when
> using a non-coupled manual diaphragm lens as you describe, no such
> communication takes place, so the responsibility for exposure
> compensation reverts to you. It's unnecessary to use an external meter.
> Instead, you can take a series of test shots at the working aperture(s)
> you plan to use, then analyze the test photos to determine the most
> desirable exposure compensation factor for each aperture. The 20D's
> auto
> exposure bracketing (AEB) function speeds up the process of taking the
> test photos, and you can use the Info palette in Photoshop to determine
> the most accurate exposure. If you can standardize on one particular
> aperture you plan to use (for maximum sharpness, desired depth of
> field,
> etc.), that will simplify the calibration process by eliminating the
> need for tests at other apertures.
> 
> Cheers
> Douglas 

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