Archived posting to the Leica Users Group, 2013/10/02
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Oct 2, 2013, at 7:58 AM, Leowesson <leowesson at gmail.com> wrote: > I think I'm the only naysayer on this, but I would never use auto ISO. It > makes no sense to me! Seems simple enough....use auto ISO if you want the camera to be "in charge" and make this decision. If you wish to be in charge of a truly manual camera, to make all the decisions, you don't use auto ISO. Steve > > 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. >> >> >> >> >> >> _______________________________________________ >> 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