Archived posting to the Leica Users Group, 2013/10/02

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Subject: [Leica] Auto ISO
From: john at mcmaster.co.nz (John McMaster)
Date: Thu, 3 Oct 2013 06:34:46 +0000
References: <D081BEA2-0FD5-4700-95E9-F125B060C7E1@acm.org> <CAAsXt4OyjVt4N5Cx4fgjYkbSN5Lo37iVPXC=O_3FppC62BFBCA@mail.gmail.com> <80F9701439F20347874CE5E4E03C22E9CDE2ACC3@WhizzMAIL01.whizz.org>, <0171C3C9-D25D-4852-BBAA-03695B57B4B6@acm.org>

I will stick to my all manual approach thanks ;-)

john
________________________________________


That's where you use exposure compensation. Shoot a white swan: increase 
exposure by compensation or any automatic system will want it to be gray. 
Shoot a black cat and decrease exposure for same reason.

Herbert Kanner
kanner at acm.org
650-326-8204

Question authority and the authorities will question you.




On Oct 2, 2013, at 12:00 PM, John McMaster <john at mcmaster.co.nz> wrote:

> I cannot see how it would? There I am putting an exposure in for a 
> silhouette and the camera thinks "that's underexposed" so ups the ASA 3 or 
> 4 stops....
>
> john
>
>> -----Original Message-----
>>
>> I'll have to read again, but I don't think AutoISO works on pure manual
>> mode...
>> Would you double check also?
>> Thanks Herb,
>> Bob
>>
>>
>> On Tue, Oct 1, 2013 at 9:30 PM, Herbert Kanner <kanner at acm.org> wrote:
>>
>>> I thought a few words about how this function operates on Leica, at
>>> least on the M9, might be useful to y'all, since the Leica Manual is
>>> not the clearest on this subject.
>>>
>>> Let's start with an understanding of the relationship between the
>>> three
>>> parameters: ISO, f-number, and shutter speed. We are used to thinking
>>> of exposure having one degree of freedom for a correct exposure. That
>>> is because we are used, from years of experience with film, of
>>> thinking of ISO being a constant. You can't change ISO in the middle
>>> of a roll of film. So, for any situation, there is one degree of freedom 
>>> for a
>> "correct" exposure:
>>> you change shutter speed, you have to change aperture, and vice versa.
>>> Hence, for the little all-electronic cameras where both the aperture
>>> and shutter are under computer control, you can choose the aperture
>>> (aperture preferred), or you can chose the shutter speed (shutter
>>> speed preferred) and the camera choses the one you didn't chose. You
>>> all know this; I'm just being pedantic.  Oh, then these idiot cameras
>>> have "programmed" mode where the camera chooses both based on
>> some arcane set of rules. That's for bozos.
>>>
>>> Now, lets look at the Leica. The camera can control the shutter, but
>>> it can't control the aperture. So the only automatic mode would appear
>>> to be aperture preferred. Ah, but the ISO is under the control of the
>>> camera's computer. It is now a third variable: it can be changed at
>>> any time. So, Leica in its wisdom invented Auto ISO. Now we have two
>> degrees of freedom.
>>> That is, we can pick the values of any two: say ISO and aperture, and
>>> now the shutter speed is determined. Thus, on the Leica, we now have a
>>> way of doing shutter speed preferred: set the shutter to the speed you
>>> want, set the aperture to the f-number you want, and the camera will
>>> pick an ISO that gives the correct exposure. So, what happens if you
>>> set Auto ISO and aperture preferred on the M9? You will be in s
>>> situation similar to program mode in a point and shoot. The camera
>>> will chose both the shutter speed and the ISO value. I took a few
>>> shots at three consecutive stops on the dial, and the shutter speed
>>> sat at 1  /150, perhaps not what I would want with a 90mm.
>>>
>>> If you set a shutter speed and an f stop with Auto ISO, everything
>>> works fine as long as the ISO that gives "correct" exposure is in the
>>> available ISO range. And you can use exposure compensation. What you
>>> lose is any information about exposure in the viewfinder. What
>>> information could that be? The ISO the camera selects, of course.
>>>
>>> One warning: the little dot and triangles used for manual exposure
>>> setting seem to be meaningless with Auto ISO: just ignore them.
>>>
>>> Herbert Kanner
>>> kanner at acm.org
>>> 650-326-8204
>>>


In reply to: Message from kanner at acm.org (Herbert Kanner) ([Leica] Auto ISO)
Message from rgacpa at gmail.com (Robert Adler) ([Leica] Auto ISO)
Message from john at mcmaster.co.nz (John McMaster) ([Leica] Auto ISO)
Message from kanner at acm.org (Herbert Kanner) ([Leica] Auto ISO)