Archived posting to the Leica Users Group, 2013/10/02
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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 > > Question authority and the authorities will question you. > > > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > -- Bob Adler