Archived posting to the Leica Users Group, 2010/11/18

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Subject: [Leica] Canon non-linear metering
From: douglas.sharp at gmx.de (Douglas Sharp)
Date: Thu, 18 Nov 2010 19:05:04 +0100
References: <mailman.647.1290096232.88697.lug@leica-users.org> <SNT121-DS59D242ADCC7509A0EA619D4390@phx.gbl>

Hi Aram,

It's a problem that's been known for a long time - in 
Canon cameras, the metering sytem compensates for the 
apertures and focal lengths that are transmitted to its 
processor from Canon and other brand AF lenses and it 
adjusts the exposure parameters to match.

Of course you are not getting this information when 
using adapted lenses, so it's correcting for a maximum 
aperture all the time (the 20D sets it at f1.8) which 
is why the difference is small for apertures closer to 
f1.8.

So it's probably not only a difference in exposure 
between max and min aperture, but also different from 
lens to lens - can anyone confirm this?

I have heard that there are programmable adapters, but 
I've never seen one.

I don't encounter the problem much because I tend to 
shoot predominantly with wide-angle lenses and I don't 
need to stop down much for DOF.

Cheers
Douglas

On 18.11.2010 18:05, Aram Langhans wrote:
> OK.  Here is a quick demonstration of what a Canon 
> camera does with a Leica lens as far as metering goes.
>
> http://gallery.leica-users.org/v/Aram/misc/meter+comparison.jpg.html 
>
>
> Nothing fancy, just the wall in my room.  Shot raw on 
> my Rebel XTi with absolutely no post processing, so 
> not very photogenic, but gets the point across.
>
> Set camera to Aperture priority mode.  Opened lens, 
> 50 Sumicron, to 2.0 and took a shot.  Meter showed as 
> centered.  Stopped down one stop and took another, 
> meter still showing as centered.  Repeated all the 
> way to f-ll, and meter still shows the camera is 
> picking an appropriate shutter speed to keep meter 
> centered.  As you can see, from f-4 on, the meter is 
> not choosing the correct shutter speed.  It starts to 
> over expose and continues to do so more and more.  If 
> I had gone to f-16, it would be even more overexposed.
>
> So, the only way to get consistent results is to 
> meter wide open in manual mode, then count down to 
> the f-stop you want, and adjust the shutter the same 
> number of counts, ignoring what the meter is telling 
> you.  It will say you are underexposing the shot, but 
> it will be the correct exposure when you see the 
> picture.
>
> Clear???
>
> Aram
>
>
>
>> From: Tim Gray <tgray at 125px.com>
>> Subject: Re: [Leica] DMR or Nikon D700 and Leitax 
>> adapters
>> To: Leica Users Group <lug at leica-users.org>
>> Message-ID: <20101118035639.GD60960 at selenium.125px.com>
>> Content-Type: text/plain; charset=us-ascii; 
>> format=flowed
>>
>> On Nov 17, 2010 at 10:03 PM -0500, Vick Ko wrote:
>>> I'm going to have to educate myself on the 
>>> "non-linear exposure issues".
>>> Sounds like a PITA.
>>
>> Yes.  Info?  Links?
>>
>
>
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for 
> more information
>


In reply to: Message from leicar at q.com (Aram Langhans) ([Leica] Canon non-linear metering)