[Leica] Auto ISO

[leowesson at gmail.com (Leowesson)]

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
> 
> Question authority and the authorities will question you.
> 
> 
> 
> 
> 
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