[Leica] Auto ISO

[john at mcmaster.co.nz (John McMaster)]

You are not alone ;-) Well I use it on snap cameras where I have less 
control/concern but not on the Leica's

john

> -----Original Message-----
> 
> I think I'm the only naysayer on this, but I would never use auto ISO.  It
> makes no sense to me!
> 
> Leo Wesson
> www.leowesson.com
> 
> > On Oct 1, 2013, at 23:30, 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
> >