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 will stick to my all manual approach thanks ;-) john ________________________________________ That's where you use exposure compensation. Shoot a white swan: increase exposure by compensation or any automatic system will want it to be gray. Shoot a black cat and decrease exposure for same reason. Herbert Kanner kanner at acm.org 650-326-8204 Question authority and the authorities will question you. On Oct 2, 2013, at 12:00 PM, John McMaster <john at mcmaster.co.nz> wrote: > I cannot see how it would? There I am putting an exposure in for a > silhouette and the camera thinks "that's underexposed" so ups the ASA 3 or > 4 stops.... > > john > >> -----Original Message----- >> >> 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 >>>