[Leica] Auto ISO

[sonc.hegr at gmail.com (Sonny Carter)]

First argument I ever got into in the LUG was over the black cat thing.  At
the time, I think I was the only person with a black cat.  It depends on
the circumstances.

http://www.sonc.com/belinna_guards.htm


On Thu, Oct 3, 2013 at 1:34 AM, Herbert Kanner <kanner at acm.org> wrote:

> 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
> >>>
> >
> >
> > _______________________________________________
> > Leica Users Group.
> > See http://leica-users.org/mailman/listinfo/lug for more information
>
>
> _______________________________________________
> Leica Users Group.
> See http://leica-users.org/mailman/listinfo/lug for more information
>



-- 
Regards,

Sonny
http://sonc.com/look/
Natchitoches, Louisiana
1714
Oldest Permanent Settlement in the Louisiana Purchase

USA