Archived posting to the Leica Users Group, 2013/10/02
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Herbert Kanner kanner at acm.org 650-326-8204 Question authority and the authorities will question you. On Oct 2, 2013, at 7:51 AM, Robert Adler <rgacpa at gmail.com> wrote: > 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 > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information